From 67c3608d00fb70aa7124c0c671ba281e4dbc5a57 Mon Sep 17 00:00:00 2001
From: Cameron Lee <calee@linkedin.com>
Date: Mon, 17 Sep 2018 17:25:18 -0700
Subject: [PATCH 1/4] SAMZA-1880: Rename non-metrics classes which use Timer in
 their name

---
 .../{TimerRegistry.java => KeyScheduler.java} | 22 +++---
 .../functions/SchedulingFunction.java         | 67 +++++++++++++++++++
 .../operators/functions/TimerFunction.java    | 65 ------------------
 .../SchedulingCallback.java}                  | 19 ++++--
 .../org/apache/samza/task/TaskContext.java    | 19 +++---
 .../samza/container/TaskContextImpl.java      |  6 +-
 .../samza/operators/impl/OperatorImpl.java    | 26 +++----
 .../operators/impl/OperatorImplGraph.java     |  8 +--
 .../operators/impl/WindowOperatorImpl.java    |  2 +-
 .../operators/spec/BroadcastOperatorSpec.java |  4 +-
 .../operators/spec/FilterOperatorSpec.java    |  6 +-
 .../operators/spec/FlatMapOperatorSpec.java   |  6 +-
 .../operators/spec/InputOperatorSpec.java     |  4 +-
 .../operators/spec/JoinOperatorSpec.java      |  6 +-
 .../samza/operators/spec/MapOperatorSpec.java |  6 +-
 .../operators/spec/MergeOperatorSpec.java     |  4 +-
 .../samza/operators/spec/OperatorSpec.java    |  4 +-
 .../operators/spec/OutputOperatorSpec.java    |  4 +-
 .../spec/PartitionByOperatorSpec.java         | 12 ++--
 .../spec/SendToTableOperatorSpec.java         |  4 +-
 .../operators/spec/SinkOperatorSpec.java      |  6 +-
 .../spec/StreamTableJoinOperatorSpec.java     |  6 +-
 .../operators/spec/WindowOperatorSpec.java    | 30 ++++-----
 .../org/apache/samza/task/AsyncRunLoop.java   | 64 +++++++++---------
 .../samza/task/SystemTimerScheduler.java      |  9 +--
 .../apache/samza/container/TaskInstance.scala |  7 +-
 .../operators/TestOperatorSpecGraph.java      |  4 +-
 .../operators/impl/TestOperatorImpl.java      |  4 +-
 .../operators/spec/OperatorSpecTestUtils.java | 10 +--
 .../operators/spec/TestOperatorSpec.java      | 37 +++++-----
 .../spec/TestPartitionByOperatorSpec.java     | 26 +++----
 .../spec/TestWindowOperatorSpec.java          | 47 ++++++-------
 .../samza/task/TestSystemTimerScheduler.java  |  2 +-
 .../sql/translator/TestProjectTranslator.java |  4 +-
 .../{TimerTest.java => SchedulingTest.java}   |  6 +-
 ...stTimerApp.java => TestSchedulingApp.java} | 23 ++++---
 36 files changed, 297 insertions(+), 282 deletions(-)
 rename samza-api/src/main/java/org/apache/samza/operators/{TimerRegistry.java => KeyScheduler.java} (63%)
 create mode 100644 samza-api/src/main/java/org/apache/samza/operators/functions/SchedulingFunction.java
 delete mode 100644 samza-api/src/main/java/org/apache/samza/operators/functions/TimerFunction.java
 rename samza-api/src/main/java/org/apache/samza/{task/TimerCallback.java => scheduler/SchedulingCallback.java} (66%)
 rename samza-test/src/test/java/org/apache/samza/test/framework/{TimerTest.java => SchedulingTest.java} (91%)
 rename samza-test/src/test/java/org/apache/samza/test/framework/{TestTimerApp.java => TestSchedulingApp.java} (78%)

diff --git a/samza-api/src/main/java/org/apache/samza/operators/TimerRegistry.java b/samza-api/src/main/java/org/apache/samza/operators/KeyScheduler.java
similarity index 63%
rename from samza-api/src/main/java/org/apache/samza/operators/TimerRegistry.java
rename to samza-api/src/main/java/org/apache/samza/operators/KeyScheduler.java
index 64dd4ec96d..22e87d5e6d 100644
--- a/samza-api/src/main/java/org/apache/samza/operators/TimerRegistry.java
+++ b/samza-api/src/main/java/org/apache/samza/operators/KeyScheduler.java
@@ -19,23 +19,25 @@
 
 package org.apache.samza.operators;
 
+import org.apache.samza.operators.functions.SchedulingFunction;
+
+
 /**
- * Allows registering epoch-time timer callbacks from the operators.
- * See {@link org.apache.samza.operators.functions.TimerFunction} for details.
- * @param <K> type of the timer key
+ * Manages scheduling keys to be triggered later. See {@link SchedulingFunction} for details.
+ * @param <K> type of the key
  */
-public interface TimerRegistry<K> {
+public interface KeyScheduler<K> {
 
   /**
-   * Register a epoch-time timer with key.
-   * @param key unique timer key
-   * @param timestamp epoch time when the timer will be fired, in milliseconds
+   * Schedule a key to be triggered at {@code timestamp}.
+   * @param key unique key
+   * @param timestamp epoch time when the key will be triggered, in milliseconds
    */
-  void register(K key, long timestamp);
+  void schedule(K key, long timestamp);
 
   /**
-   * Delete the timer for the provided key.
-   * @param key key for the timer to delete
+   * Delete the scheduler entry for the provided key.
+   * @param key key to delete
    */
   void delete(K key);
 }
diff --git a/samza-api/src/main/java/org/apache/samza/operators/functions/SchedulingFunction.java b/samza-api/src/main/java/org/apache/samza/operators/functions/SchedulingFunction.java
new file mode 100644
index 0000000000..21cb0895b7
--- /dev/null
+++ b/samza-api/src/main/java/org/apache/samza/operators/functions/SchedulingFunction.java
@@ -0,0 +1,67 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.samza.operators.functions;
+
+import org.apache.samza.operators.KeyScheduler;
+
+import java.util.Collection;
+
+/**
+ * Allows scheduling with key(s) and is invoked when the specified time(s) occurs.
+ * Key must be a unique identifier for its corresponding logic to execute, and is provided in the callback when the
+ * corresponding schedule time occurs.
+ *
+ * <p>
+ * Example of a {@link FlatMapFunction} with {@link SchedulingFunction}:
+ * <pre>{@code
+ *    public class ExampleSchedulingFn implements FlatMapFunction<String, String>, SchedulingFunction<String, String> {
+ *      public void schedulingInit(KeyScheduler keyScheduler) {
+ *        long time = System.currentTimeMillis() + 5000; // fire after 5 sec
+ *        keyScheduler.schedule("example-scheduler-logic", time);
+ *      }
+ *      public Collection<String> apply(String s) {
+ *        ...
+ *      }
+ *      public Collection<String> executeForKey(String key, long timestamp) {
+ *        // fired with key as "example-scheduler-logic"
+ *        ...
+ *      }
+ *    }
+ * }</pre>
+ * @param <K> type of the key
+ * @param <OM> type of the output
+ */
+public interface SchedulingFunction<K, OM> {
+
+  /**
+   * Initialize the function for scheduling, such as setting some initial scheduling logic or saving the
+   * {@code keyScheduler} for later use.
+   * @param keyScheduler used to specify the schedule time(s) and key(s)
+   */
+  void schedulingInit(KeyScheduler<K> keyScheduler);
+
+  /**
+   * Returns the output from the scheduling logic corresponding to the key that was triggered.
+   * @param key key corresponding to the scheduling logic that got triggered
+   * @param timestamp schedule time that was set for the key, in milliseconds since epoch
+   * @return {@link Collection} of output elements
+   */
+  Collection<OM> executeForKey(K key, long timestamp);
+}
diff --git a/samza-api/src/main/java/org/apache/samza/operators/functions/TimerFunction.java b/samza-api/src/main/java/org/apache/samza/operators/functions/TimerFunction.java
deleted file mode 100644
index 01825c6479..0000000000
--- a/samza-api/src/main/java/org/apache/samza/operators/functions/TimerFunction.java
+++ /dev/null
@@ -1,65 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one
- * or more contributor license agreements.  See the NOTICE file
- * distributed with this work for additional information
- * regarding copyright ownership.  The ASF licenses this file
- * to you under the Apache License, Version 2.0 (the
- * "License"); you may not use this file except in compliance
- * with the License.  You may obtain a copy of the License at
- *
- *   http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing,
- * software distributed under the License is distributed on an
- * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
- * KIND, either express or implied.  See the License for the
- * specific language governing permissions and limitations
- * under the License.
- */
-
-package org.apache.samza.operators.functions;
-
-import org.apache.samza.operators.TimerRegistry;
-
-import java.util.Collection;
-
-/**
- * Allows timer registration with a key and is invoked when the timer is fired.
- * Key must be a unique identifier for this timer, and is provided in the callback when the timer fires.
- *
- * <p>
- * Example of a {@link FlatMapFunction} with timer:
- * <pre>{@code
- *    public class ExampleTimerFn implements FlatMapFunction<String, String>, TimerFunction<String, String> {
- *      public void registerTimer(TimerRegistry timerRegistry) {
- *        long time = System.currentTimeMillis() + 5000; // fire after 5 sec
- *        timerRegistry.register("example-timer", time);
- *      }
- *      public Collection<String> apply(String s) {
- *        ...
- *      }
- *      public Collection<String> onTimer(String key, long timestamp) {
- *        // example-timer fired
- *        ...
- *      }
- *    }
- * }</pre>
- * @param <K> type of the key
- * @param <OM> type of the output
- */
-public interface TimerFunction<K, OM> {
-
-  /**
-   * Registers any epoch-time timers using the registry
-   * @param timerRegistry a keyed {@link TimerRegistry}
-   */
-  void registerTimer(TimerRegistry<K> timerRegistry);
-
-  /**
-   * Returns the output after the timer with key fires.
-   * @param key timer key
-   * @param timestamp time of the epoch-time timer fired, in milliseconds
-   * @return {@link Collection} of output elements
-   */
-  Collection<OM> onTimer(K key, long timestamp);
-}
diff --git a/samza-api/src/main/java/org/apache/samza/task/TimerCallback.java b/samza-api/src/main/java/org/apache/samza/scheduler/SchedulingCallback.java
similarity index 66%
rename from samza-api/src/main/java/org/apache/samza/task/TimerCallback.java
rename to samza-api/src/main/java/org/apache/samza/scheduler/SchedulingCallback.java
index 3add129c63..34a5341f0e 100644
--- a/samza-api/src/main/java/org/apache/samza/task/TimerCallback.java
+++ b/samza-api/src/main/java/org/apache/samza/scheduler/SchedulingCallback.java
@@ -17,18 +17,23 @@
  * under the License.
  */
 
-package org.apache.samza.task;
+package org.apache.samza.scheduler;
+
+import org.apache.samza.task.MessageCollector;
+import org.apache.samza.task.TaskCoordinator;
+
 
 /**
- * The callback that is invoked when its corresponding timer registered via {@link TaskContext} fires.
- * @param <K> type of the timer key
+ * The callback that is invoked when its corresponding schedule time registered via
+ * {@link org.apache.samza.task.TaskContext} is reached.
+ * @param <K> type of the callback key
  */
-public interface TimerCallback<K> {
+public interface SchedulingCallback<K> {
   /**
-   * Invoked when the timer of key fires.
-   * @param key timer key
+   * Invoked when the corresponding schedule time is reached.
+   * @param key key for callback
    * @param collector contains the means of sending message envelopes to the output stream.
    * @param coordinator manages execution of tasks.
    */
-  void onTimer(K key, MessageCollector collector, TaskCoordinator coordinator);
+  void execute(K key, MessageCollector collector, TaskCoordinator coordinator);
 }
diff --git a/samza-api/src/main/java/org/apache/samza/task/TaskContext.java b/samza-api/src/main/java/org/apache/samza/task/TaskContext.java
index ea2a3bca98..32b9be3aa6 100644
--- a/samza-api/src/main/java/org/apache/samza/task/TaskContext.java
+++ b/samza-api/src/main/java/org/apache/samza/task/TaskContext.java
@@ -24,6 +24,7 @@
 import org.apache.samza.container.SamzaContainerContext;
 import org.apache.samza.container.TaskName;
 import org.apache.samza.metrics.MetricsRegistry;
+import org.apache.samza.scheduler.SchedulingCallback;
 import org.apache.samza.system.SystemStreamPartition;
 import org.apache.samza.table.Table;
 
@@ -76,21 +77,21 @@ default Object getUserContext() {
   }
 
   /**
-   * Register a keyed timer with a callback of {@link TimerCallback} in this task.
+   * Register a keyed callback in this task.
    * The callback will be invoked exclusively with any other operations for this task,
    * e.g. processing, windowing and commit.
-   * @param key timer key
-   * @param timestamp epoch time when the timer will be fired, in milliseconds
-   * @param callback callback when the timer is fired
+   * @param key key for the callback
+   * @param timestamp epoch time when the callback will be fired, in milliseconds
+   * @param callback callback to call when the {@code timestamp} is reached
    * @param <K> type of the key
    */
-  <K> void registerTimer(K key, long timestamp, TimerCallback<K> callback);
+  <K> void scheduleCallback(K key, long timestamp, SchedulingCallback<K> callback);
 
   /**
-   * Delete the keyed timer in this task.
-   * Deletion only happens if the timer hasn't been fired. Otherwise it will not interrupt.
-   * @param key timer key
+   * Delete the keyed callback in this task.
+   * Deletion only happens if the callback hasn't been fired. Otherwise it will not interrupt.
+   * @param key callback key
    * @param <K> type of the key
    */
-  <K> void deleteTimer(K key);
+  <K> void deleteScheduledCallback(K key);
 }
diff --git a/samza-core/src/main/java/org/apache/samza/container/TaskContextImpl.java b/samza-core/src/main/java/org/apache/samza/container/TaskContextImpl.java
index d65be4cbbb..05f849099d 100644
--- a/samza-core/src/main/java/org/apache/samza/container/TaskContextImpl.java
+++ b/samza-core/src/main/java/org/apache/samza/container/TaskContextImpl.java
@@ -31,7 +31,7 @@
 import org.apache.samza.table.TableManager;
 import org.apache.samza.task.SystemTimerScheduler;
 import org.apache.samza.task.TaskContext;
-import org.apache.samza.task.TimerCallback;
+import org.apache.samza.scheduler.SchedulingCallback;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -134,12 +134,12 @@ public Object getUserContext() {
   }
 
   @Override
-  public <K> void registerTimer(K key, long timestamp, TimerCallback<K> callback) {
+  public <K> void scheduleCallback(K key, long timestamp, SchedulingCallback<K> callback) {
     timerScheduler.setTimer(key, timestamp, callback);
   }
 
   @Override
-  public <K> void deleteTimer(K key) {
+  public <K> void deleteScheduledCallback(K key) {
     timerScheduler.deleteTimer(key);
   }
 
diff --git a/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImpl.java b/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImpl.java
index f0c099794a..851b48f012 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImpl.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImpl.java
@@ -25,8 +25,8 @@
 import org.apache.samza.container.TaskName;
 import org.apache.samza.job.model.ContainerModel;
 import org.apache.samza.job.model.TaskModel;
-import org.apache.samza.operators.TimerRegistry;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.KeyScheduler;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.system.EndOfStreamMessage;
 import org.apache.samza.metrics.Counter;
@@ -436,19 +436,19 @@ final long getOutputWatermark() {
 
   /**
    * Returns a registry which allows registering arbitrary system-clock timer with K-typed key.
-   * The user-defined function in the operator spec needs to implement {@link TimerFunction#onTimer(Object, long)}
+   * The user-defined function in the operator spec needs to implement {@link SchedulingFunction#executeForKey(Object, long)}
    * for timer notifications.
    * @param <K> key type for the timer.
-   * @return an instance of {@link TimerRegistry}
+   * @return an instance of {@link KeyScheduler}
    */
-  <K> TimerRegistry<K> createOperatorTimerRegistry() {
-    return new TimerRegistry<K>() {
+  <K> KeyScheduler<K> createOperatorKeyScheduler() {
+    return new KeyScheduler<K>() {
       @Override
-      public void register(K key, long time) {
-        taskContext.registerTimer(key, time, (k, collector, coordinator) -> {
-            final TimerFunction<K, RM> timerFn = getOperatorSpec().getTimerFn();
-            if (timerFn != null) {
-              final Collection<RM> output = timerFn.onTimer(key, time);
+      public void schedule(K key, long time) {
+        taskContext.scheduleCallback(key, time, (k, collector, coordinator) -> {
+            final SchedulingFunction<K, RM> schedulingFn = getOperatorSpec().getSchedulingFn();
+            if (schedulingFn != null) {
+              final Collection<RM> output = schedulingFn.executeForKey(key, time);
 
               if (!output.isEmpty()) {
                 output.forEach(rm ->
@@ -457,7 +457,7 @@ public void register(K key, long time) {
               }
             } else {
               throw new SamzaException(
-                  String.format("Operator %s id %s (created at %s) must implement TimerFunction to use system timer.",
+                  String.format("Operator %s id %s (created at %s) must implement SchedulingFunction to use system timer.",
                       getOperatorSpec().getOpCode().name(), getOpImplId(), getOperatorSpec().getSourceLocation()));
             }
           });
@@ -465,7 +465,7 @@ public void register(K key, long time) {
 
       @Override
       public void delete(K key) {
-        taskContext.deleteTimer(key);
+        taskContext.deleteScheduledCallback(key);
       }
     };
   }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImplGraph.java b/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImplGraph.java
index 7f62e00742..13b1fc593e 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImplGraph.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImplGraph.java
@@ -26,7 +26,7 @@
 import org.apache.samza.container.TaskContextImpl;
 import org.apache.samza.job.model.JobModel;
 import org.apache.samza.operators.KV;
-import org.apache.samza.operators.TimerRegistry;
+import org.apache.samza.operators.KeyScheduler;
 import org.apache.samza.operators.functions.JoinFunction;
 import org.apache.samza.operators.functions.PartialJoinFunction;
 import org.apache.samza.util.TimestampedValue;
@@ -170,9 +170,9 @@ private OperatorImpl createAndRegisterOperatorImpl(OperatorSpec prevOperatorSpec
       operatorImpl.init(config, context);
       operatorImpl.registerInputStream(inputStream);
 
-      if (operatorSpec.getTimerFn() != null) {
-        final TimerRegistry timerRegistry = operatorImpl.createOperatorTimerRegistry();
-        operatorSpec.getTimerFn().registerTimer(timerRegistry);
+      if (operatorSpec.getSchedulingFn() != null) {
+        final KeyScheduler keyScheduler = operatorImpl.createOperatorKeyScheduler();
+        operatorSpec.getSchedulingFn().schedulingInit(keyScheduler);
       }
 
       // Note: The key here is opImplId, which may not equal opId for some impls (e.g. PartialJoinOperatorImpl).
diff --git a/samza-core/src/main/java/org/apache/samza/operators/impl/WindowOperatorImpl.java b/samza-core/src/main/java/org/apache/samza/operators/impl/WindowOperatorImpl.java
index 82dc0bf2b7..b175671e9a 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/impl/WindowOperatorImpl.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/impl/WindowOperatorImpl.java
@@ -183,7 +183,7 @@ public Collection<WindowPane<K, Object>> handleMessage(
 
   @Override
   public Collection<WindowPane<K, Object>> handleTimer(MessageCollector collector, TaskCoordinator coordinator) {
-    LOG.trace("Processing timer.");
+    LOG.trace("Processing time triggers");
     List<WindowPane<K, Object>> results = new ArrayList<>();
     List<TriggerKey<K>> keys = triggerScheduler.runPendingCallbacks();
 
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/BroadcastOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/BroadcastOperatorSpec.java
index 2c76e600a2..abc9bee0c7 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/BroadcastOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/BroadcastOperatorSpec.java
@@ -20,7 +20,7 @@
 
 package org.apache.samza.operators.spec;
 
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 
 public class BroadcastOperatorSpec<M> extends OperatorSpec<M, Void> {
@@ -43,7 +43,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public TimerFunction getTimerFn() {
+  public SchedulingFunction getSchedulingFn() {
     return null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/FilterOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/FilterOperatorSpec.java
index a5cdb82e5e..b26f914ee6 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/FilterOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/FilterOperatorSpec.java
@@ -23,7 +23,7 @@
 import org.apache.samza.config.Config;
 import org.apache.samza.operators.functions.FilterFunction;
 import org.apache.samza.operators.functions.FlatMapFunction;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.task.TaskContext;
 
@@ -68,7 +68,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public TimerFunction getTimerFn() {
-    return this.filterFn instanceof TimerFunction ? (TimerFunction) this.filterFn : null;
+  public SchedulingFunction getSchedulingFn() {
+    return this.filterFn instanceof SchedulingFunction ? (SchedulingFunction) this.filterFn : null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/FlatMapOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/FlatMapOperatorSpec.java
index a93a2215f5..d52dc0ff2a 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/FlatMapOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/FlatMapOperatorSpec.java
@@ -19,7 +19,7 @@
 package org.apache.samza.operators.spec;
 
 import org.apache.samza.operators.functions.FlatMapFunction;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 
 
@@ -41,7 +41,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public TimerFunction getTimerFn() {
-    return this.transformFn instanceof TimerFunction ? (TimerFunction) this.transformFn : null;
+  public SchedulingFunction getSchedulingFn() {
+    return this.transformFn instanceof SchedulingFunction ? (SchedulingFunction) this.transformFn : null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/InputOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/InputOperatorSpec.java
index c49443de70..afb8266994 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/InputOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/InputOperatorSpec.java
@@ -19,7 +19,7 @@
 package org.apache.samza.operators.spec;
 
 import org.apache.samza.operators.functions.InputTransformer;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.serializers.Serde;
 import org.apache.samza.system.IncomingMessageEnvelope;
@@ -99,7 +99,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public TimerFunction getTimerFn() {
+  public SchedulingFunction getSchedulingFn() {
     return null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/JoinOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/JoinOperatorSpec.java
index 1b55784687..5bb64e44ce 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/JoinOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/JoinOperatorSpec.java
@@ -20,7 +20,7 @@
 
 import com.google.common.collect.ImmutableMap;
 import org.apache.samza.operators.functions.JoinFunction;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.operators.impl.store.TimestampedValueSerde;
 import org.apache.samza.util.TimestampedValue;
@@ -105,8 +105,8 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public TimerFunction getTimerFn() {
-    return joinFn instanceof TimerFunction ? (TimerFunction) joinFn : null;
+  public SchedulingFunction getSchedulingFn() {
+    return joinFn instanceof SchedulingFunction ? (SchedulingFunction) joinFn : null;
   }
 
   public OperatorSpec getLeftInputOpSpec() {
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/MapOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/MapOperatorSpec.java
index 1e2190bd27..36a55422fc 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/MapOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/MapOperatorSpec.java
@@ -23,7 +23,7 @@
 import org.apache.samza.config.Config;
 import org.apache.samza.operators.functions.FlatMapFunction;
 import org.apache.samza.operators.functions.MapFunction;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.task.TaskContext;
 
@@ -71,7 +71,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public TimerFunction getTimerFn() {
-    return this.mapFn instanceof TimerFunction ? (TimerFunction) this.mapFn : null;
+  public SchedulingFunction getSchedulingFn() {
+    return this.mapFn instanceof SchedulingFunction ? (SchedulingFunction) this.mapFn : null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/MergeOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/MergeOperatorSpec.java
index 987f72cfca..18dd15ea36 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/MergeOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/MergeOperatorSpec.java
@@ -19,7 +19,7 @@
 package org.apache.samza.operators.spec;
 
 import java.util.ArrayList;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 
 
@@ -45,7 +45,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public TimerFunction getTimerFn() {
+  public SchedulingFunction getSchedulingFn() {
     return null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/OperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/OperatorSpec.java
index 1e021f564c..6cd16cf17c 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/OperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/OperatorSpec.java
@@ -25,7 +25,7 @@
 import org.apache.samza.annotation.InterfaceStability;
 import org.apache.samza.operators.MessageStream;
 import org.apache.samza.operators.MessageStreamImpl;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 
 /**
@@ -143,5 +143,5 @@ public final String getSourceLocation() {
 
   abstract public WatermarkFunction getWatermarkFn();
 
-  abstract public TimerFunction getTimerFn();
+  abstract public SchedulingFunction getSchedulingFn();
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/OutputOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/OutputOperatorSpec.java
index 40a5c0ec06..3487b1a8f8 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/OutputOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/OutputOperatorSpec.java
@@ -19,7 +19,7 @@
 package org.apache.samza.operators.spec;
 
 
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 
 /**
@@ -59,7 +59,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public TimerFunction getTimerFn() {
+  public SchedulingFunction getSchedulingFn() {
     return null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/PartitionByOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/PartitionByOperatorSpec.java
index d6bf3d94a5..dee72e392e 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/PartitionByOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/PartitionByOperatorSpec.java
@@ -20,7 +20,7 @@
 
 import org.apache.samza.operators.KV;
 import org.apache.samza.operators.functions.MapFunction;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 
 import static com.google.common.base.Preconditions.checkArgument;
@@ -55,10 +55,10 @@ public class PartitionByOperatorSpec<M, K, V> extends OperatorSpec<M, Void> {
       MapFunction<? super M, ? extends K> keyFunction,
       MapFunction<? super M, ? extends V> valueFunction, String opId) {
     super(OpCode.PARTITION_BY, opId);
-    checkArgument(!(keyFunction instanceof TimerFunction || keyFunction instanceof WatermarkFunction),
-        "keyFunction for partitionBy should not implement TimerFunction or WatermarkFunction.");
-    checkArgument(!(valueFunction instanceof TimerFunction || valueFunction instanceof WatermarkFunction),
-        "valueFunction for partitionBy should not implement TimerFunction or WatermarkFunction.");
+    checkArgument(!(keyFunction instanceof SchedulingFunction || keyFunction instanceof WatermarkFunction),
+        "keyFunction for partitionBy should not implement SchedulingFunction or WatermarkFunction.");
+    checkArgument(!(valueFunction instanceof SchedulingFunction || valueFunction instanceof WatermarkFunction),
+        "valueFunction for partitionBy should not implement SchedulingFunction or WatermarkFunction.");
     this.outputStream = outputStream;
     this.keyFunction = keyFunction;
     this.valueFunction = valueFunction;
@@ -86,7 +86,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public TimerFunction getTimerFn() {
+  public SchedulingFunction getSchedulingFn() {
     return null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/SendToTableOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/SendToTableOperatorSpec.java
index 22f393ece6..5a11a66ec0 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/SendToTableOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/SendToTableOperatorSpec.java
@@ -20,7 +20,7 @@
 
 import org.apache.samza.annotation.InterfaceStability;
 import org.apache.samza.operators.KV;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.table.TableSpec;
 
@@ -58,7 +58,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public TimerFunction getTimerFn() {
+  public SchedulingFunction getSchedulingFn() {
     return null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/SinkOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/SinkOperatorSpec.java
index aa0f066947..b27f8a8351 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/SinkOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/SinkOperatorSpec.java
@@ -19,7 +19,7 @@
 package org.apache.samza.operators.spec;
 
 import org.apache.samza.operators.functions.SinkFunction;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 
 
@@ -57,7 +57,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public TimerFunction getTimerFn() {
-    return sinkFn instanceof TimerFunction ? (TimerFunction) sinkFn : null;
+  public SchedulingFunction getSchedulingFn() {
+    return sinkFn instanceof SchedulingFunction ? (SchedulingFunction) sinkFn : null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/StreamTableJoinOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/StreamTableJoinOperatorSpec.java
index c7735c6d77..28018d32f7 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/StreamTableJoinOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/StreamTableJoinOperatorSpec.java
@@ -19,8 +19,8 @@
 package org.apache.samza.operators.spec;
 
 import org.apache.samza.annotation.InterfaceStability;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.StreamTableJoinFunction;
-import org.apache.samza.operators.functions.TimerFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.table.TableSpec;
 
@@ -66,8 +66,8 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public TimerFunction getTimerFn() {
-    return joinFn instanceof TimerFunction ? (TimerFunction) joinFn : null;
+  public SchedulingFunction getSchedulingFn() {
+    return joinFn instanceof SchedulingFunction ? (SchedulingFunction) joinFn : null;
   }
 
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/WindowOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/WindowOperatorSpec.java
index 8d1ad2989d..f4a074a224 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/WindowOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/WindowOperatorSpec.java
@@ -20,7 +20,7 @@
 package org.apache.samza.operators.spec;
 
 import org.apache.samza.operators.functions.FoldLeftFunction;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.operators.impl.store.TimeSeriesKeySerde;
 import org.apache.samza.operators.triggers.AnyTrigger;
@@ -64,14 +64,14 @@ public class WindowOperatorSpec<M, WK, WV> extends OperatorSpec<M, WindowPane<WK
   WindowOperatorSpec(WindowInternal<M, WK, WV> window, String opId) {
     super(OpCode.WINDOW, opId);
     checkArgument(window.getInitializer() == null ||
-        !(window.getInitializer() instanceof TimerFunction || window.getInitializer() instanceof WatermarkFunction),
-        "A window does not accepts a user-defined TimerFunction or WatermarkFunction as the initializer.");
+        !(window.getInitializer() instanceof SchedulingFunction || window.getInitializer() instanceof WatermarkFunction),
+        "A window does not accepts a user-defined SchedulingFunction or WatermarkFunction as the initializer.");
     checkArgument(window.getKeyExtractor() == null ||
-        !(window.getKeyExtractor() instanceof TimerFunction || window.getKeyExtractor() instanceof WatermarkFunction),
-        "A window does not accepts a user-defined TimerFunction or WatermarkFunction as the keyExtractor.");
+        !(window.getKeyExtractor() instanceof SchedulingFunction || window.getKeyExtractor() instanceof WatermarkFunction),
+        "A window does not accepts a user-defined SchedulingFunction or WatermarkFunction as the keyExtractor.");
     checkArgument(window.getEventTimeExtractor() == null ||
-        !(window.getEventTimeExtractor() instanceof TimerFunction || window.getEventTimeExtractor() instanceof WatermarkFunction),
-        "A window does not accepts a user-defined TimerFunction or WatermarkFunction as the eventTimeExtractor.");
+        !(window.getEventTimeExtractor() instanceof SchedulingFunction || window.getEventTimeExtractor() instanceof WatermarkFunction),
+        "A window does not accepts a user-defined SchedulingFunction or WatermarkFunction as the eventTimeExtractor.");
     this.window = window;
   }
 
@@ -88,21 +88,21 @@ public WindowInternal<M, WK, WV> getWindow() {
    * @return the default triggering interval
    */
   public long getDefaultTriggerMs() {
-    List<TimeBasedTrigger> timerTriggers = new ArrayList<>();
+    List<TimeBasedTrigger> timeBasedTriggers = new ArrayList<>();
 
     if (window.getDefaultTrigger() != null) {
-      timerTriggers.addAll(getTimeBasedTriggers(window.getDefaultTrigger()));
+      timeBasedTriggers.addAll(getTimeBasedTriggers(window.getDefaultTrigger()));
     }
     if (window.getEarlyTrigger() != null) {
-      timerTriggers.addAll(getTimeBasedTriggers(window.getEarlyTrigger()));
+      timeBasedTriggers.addAll(getTimeBasedTriggers(window.getEarlyTrigger()));
     }
     if (window.getLateTrigger() != null) {
-      timerTriggers.addAll(getTimeBasedTriggers(window.getLateTrigger()));
+      timeBasedTriggers.addAll(getTimeBasedTriggers(window.getLateTrigger()));
     }
 
-    LOG.info("Got {} timer triggers", timerTriggers.size());
+    LOG.info("Got {} time-based triggers", timeBasedTriggers.size());
 
-    List<Long> candidateDurations = timerTriggers.stream()
+    List<Long> candidateDurations = timeBasedTriggers.stream()
         .map(timeBasedTrigger -> timeBasedTrigger.getDuration().toMillis())
         .collect(Collectors.toList());
 
@@ -135,9 +135,9 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public TimerFunction getTimerFn() {
+  public SchedulingFunction getSchedulingFn() {
     FoldLeftFunction fn = window.getFoldLeftFunction();
-    return fn instanceof TimerFunction ? (TimerFunction) fn : null;
+    return fn instanceof SchedulingFunction ? (SchedulingFunction) fn : null;
   }
 
   @Override
diff --git a/samza-core/src/main/java/org/apache/samza/task/AsyncRunLoop.java b/samza-core/src/main/java/org/apache/samza/task/AsyncRunLoop.java
index 3b3e008460..dc98d204e5 100644
--- a/samza-core/src/main/java/org/apache/samza/task/AsyncRunLoop.java
+++ b/samza-core/src/main/java/org/apache/samza/task/AsyncRunLoop.java
@@ -330,7 +330,7 @@ private enum WorkerOp {
     COMMIT,
     PROCESS,
     END_OF_STREAM,
-    TIMER,
+    SCHEDULER,
     NO_OP
   }
 
@@ -374,10 +374,10 @@ public void run() {
         }, commitMs, commitMs, TimeUnit.MILLISECONDS);
       }
 
-      final SystemTimerScheduler timerFactory = task.context().getTimerScheduler();
-      if (timerFactory != null) {
-        timerFactory.registerListener(() -> {
-            state.needTimer();
+      final SystemTimerScheduler timerScheduler = task.context().getTimerScheduler();
+      if (timerScheduler != null) {
+        timerScheduler.registerListener(() -> {
+            state.needScheduler();
           });
       }
     }
@@ -409,8 +409,8 @@ private void run() {
         case WINDOW:
           window();
           break;
-        case TIMER:
-          timer();
+        case SCHEDULER:
+          scheduler();
           break;
         case COMMIT:
           commit();
@@ -551,8 +551,8 @@ public void run() {
       }
     }
 
-    private void timer() {
-      state.startTimer();
+    private void scheduler() {
+      state.startScheduler();
       Runnable timerWorker = new Runnable() {
         @Override
         public void run() {
@@ -560,26 +560,26 @@ public void run() {
             ReadableCoordinator coordinator = new ReadableCoordinator(task.taskName());
 
             long startTime = clock.nanoTime();
-            task.timer(coordinator);
+            task.scheduler(coordinator);
             containerMetrics.timerNs().update(clock.nanoTime() - startTime);
 
             coordinatorRequests.update(coordinator);
-            state.doneTimer();
+            state.doneScheduler();
           } catch (Throwable t) {
-            log.error("Task {} timer failed", task.taskName(), t);
+            log.error("Task {} scheduler failed", task.taskName(), t);
             abort(t);
           } finally {
-            log.trace("Task {} timer completed", task.taskName());
+            log.trace("Task {} scheduler completed", task.taskName());
             resume();
           }
         }
       };
 
       if (threadPool != null) {
-        log.trace("Task {} timer runs on the thread pool", task.taskName());
+        log.trace("Task {} scheduler runs on the thread pool", task.taskName());
         threadPool.submit(timerWorker);
       } else {
-        log.trace("Task {} timer runs on the run loop thread", task.taskName());
+        log.trace("Task {} scheduler runs on the run loop thread", task.taskName());
         timerWorker.run();
       }
     }
@@ -655,12 +655,12 @@ public void onFailure(TaskCallback callback, Throwable t) {
   private final class AsyncTaskState {
     private volatile boolean needWindow = false;
     private volatile boolean needCommit = false;
-    private volatile boolean needTimer = false;
+    private volatile boolean needScheduler = false;
     private volatile boolean complete = false;
     private volatile boolean endOfStream = false;
     private volatile boolean windowInFlight = false;
     private volatile boolean commitInFlight = false;
-    private volatile boolean timerInFlight = false;
+    private volatile boolean schedulerInFlight = false;
     private final AtomicInteger messagesInFlight = new AtomicInteger(0);
     private final ArrayDeque<PendingEnvelope> pendingEnvelopeQueue;
 
@@ -706,28 +706,28 @@ private boolean isReady() {
         needCommit = true;
       }
 
-      boolean opInFlight = windowInFlight || commitInFlight || timerInFlight;
+      boolean opInFlight = windowInFlight || commitInFlight || schedulerInFlight;
       /*
        * A task is ready to commit, when task.commit(needCommit) is requested either by user or commit thread
        * and either of the following conditions are true.
-       * a) When process, window, commit and timer are not in progress.
+       * a) When process, window, commit and scheduler are not in progress.
        * b) When task.async.commit is true and window, commit are not in progress.
        */
       if (needCommit) {
         return (messagesInFlight.get() == 0 || isAsyncCommitEnabled) && !opInFlight;
-      } else if (needWindow || needTimer || endOfStream) {
+      } else if (needWindow || needScheduler || endOfStream) {
         /*
-         * A task is ready for window, timer or end-of-stream operation.
+         * A task is ready for window, scheduler or end-of-stream operation.
          */
         return messagesInFlight.get() == 0 && !opInFlight;
       } else {
         /*
          * A task is ready to process new message, when number of task.process calls in progress < task.max.concurrency
          * and either of the following conditions are true.
-         * a) When window, commit and timer are not in progress.
-         * b) When task.async.commit is true and window and timer are not in progress.
+         * a) When window, commit and scheduler are not in progress.
+         * b) When task.async.commit is true and window and scheduler are not in progress.
          */
-        return messagesInFlight.get() < maxConcurrency && !windowInFlight && !timerInFlight && (isAsyncCommitEnabled || !commitInFlight);
+        return messagesInFlight.get() < maxConcurrency && !windowInFlight && !schedulerInFlight && (isAsyncCommitEnabled || !commitInFlight);
       }
     }
 
@@ -741,7 +741,7 @@ private WorkerOp nextOp() {
       if (isReady()) {
         if (needCommit) return WorkerOp.COMMIT;
         else if (needWindow) return WorkerOp.WINDOW;
-        else if (needTimer) return WorkerOp.TIMER;
+        else if (needScheduler) return WorkerOp.SCHEDULER;
         else if (endOfStream && pendingEnvelopeQueue.isEmpty()) return WorkerOp.END_OF_STREAM;
         else if (!pendingEnvelopeQueue.isEmpty()) return WorkerOp.PROCESS;
       }
@@ -756,8 +756,8 @@ private void needCommit() {
       needCommit = true;
     }
 
-    private void needTimer() {
-      needTimer = true;
+    private void needScheduler() {
+      needScheduler = true;
     }
 
     private void startWindow() {
@@ -775,9 +775,9 @@ private void startProcess() {
       taskMetrics.messagesInFlight().set(count);
     }
 
-    private void startTimer() {
-      needTimer = false;
-      timerInFlight = true;
+    private void startScheduler() {
+      needScheduler = false;
+      schedulerInFlight = true;
     }
 
     private void doneCommit() {
@@ -793,8 +793,8 @@ private void doneProcess() {
       taskMetrics.messagesInFlight().set(count);
     }
 
-    private void doneTimer() {
-      timerInFlight = false;
+    private void doneScheduler() {
+      schedulerInFlight = false;
     }
 
     /**
diff --git a/samza-core/src/main/java/org/apache/samza/task/SystemTimerScheduler.java b/samza-core/src/main/java/org/apache/samza/task/SystemTimerScheduler.java
index aa9792bdf2..eba9e583e6 100644
--- a/samza-core/src/main/java/org/apache/samza/task/SystemTimerScheduler.java
+++ b/samza-core/src/main/java/org/apache/samza/task/SystemTimerScheduler.java
@@ -25,6 +25,7 @@
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
+import org.apache.samza.scheduler.SchedulingCallback;
 
 import static com.google.common.base.Preconditions.checkState;
 
@@ -46,7 +47,7 @@ public interface TimerListener {
 
   private final ScheduledExecutorService executor;
   private final Map<Object, ScheduledFuture> scheduledFutures = new ConcurrentHashMap<>();
-  private final Map<TimerKey<?>, TimerCallback> readyTimers = new ConcurrentHashMap<>();
+  private final Map<TimerKey<?>, SchedulingCallback> readyTimers = new ConcurrentHashMap<>();
   private TimerListener timerListener;
 
   public static SystemTimerScheduler create(ScheduledExecutorService executor) {
@@ -57,7 +58,7 @@ private SystemTimerScheduler(ScheduledExecutorService executor) {
     this.executor = executor;
   }
 
-  public <K> void setTimer(K key, long timestamp, TimerCallback<K> callback) {
+  public <K> void setTimer(K key, long timestamp, SchedulingCallback<K> callback) {
     checkState(!scheduledFutures.containsKey(key),
         String.format("Duplicate key %s registration for the same timer", key));
 
@@ -84,8 +85,8 @@ void registerListener(TimerListener listener) {
     timerListener = listener;
   }
 
-  public Map<TimerKey<?>, TimerCallback> removeReadyTimers() {
-    final Map<TimerKey<?>, TimerCallback> timers = new TreeMap<>(readyTimers);
+  public Map<TimerKey<?>, SchedulingCallback> removeReadyTimers() {
+    final Map<TimerKey<?>, SchedulingCallback> timers = new TreeMap<>(readyTimers);
     readyTimers.keySet().removeAll(timers.keySet());
     return timers;
   }
diff --git a/samza-core/src/main/scala/org/apache/samza/container/TaskInstance.scala b/samza-core/src/main/scala/org/apache/samza/container/TaskInstance.scala
index d85f10f272..a3448fcece 100644
--- a/samza-core/src/main/scala/org/apache/samza/container/TaskInstance.scala
+++ b/samza-core/src/main/scala/org/apache/samza/container/TaskInstance.scala
@@ -28,6 +28,7 @@ import org.apache.samza.config.Config
 import org.apache.samza.config.StreamConfig.Config2Stream
 import org.apache.samza.job.model.JobModel
 import org.apache.samza.metrics.MetricsReporter
+import org.apache.samza.scheduler.SchedulingCallback
 import org.apache.samza.storage.kv.KeyValueStore
 import org.apache.samza.storage.{TaskSideInputStorageManager, TaskStorageManager}
 import org.apache.samza.system._
@@ -221,12 +222,12 @@ class TaskInstance(
     }
   }
 
-  def timer(coordinator: ReadableCoordinator) {
-    trace("Timer for taskName: %s" format taskName)
+  def scheduler(coordinator: ReadableCoordinator) {
+    trace("Scheduler for taskName: %s" format taskName)
 
     exceptionHandler.maybeHandle {
       context.getTimerScheduler.removeReadyTimers().entrySet().foreach { entry =>
-        entry.getValue.asInstanceOf[TimerCallback[Any]].onTimer(entry.getKey.getKey, collector, coordinator)
+        entry.getValue.asInstanceOf[SchedulingCallback[Any]].execute(entry.getKey.getKey, collector, coordinator)
       }
     }
   }
diff --git a/samza-core/src/test/java/org/apache/samza/operators/TestOperatorSpecGraph.java b/samza-core/src/test/java/org/apache/samza/operators/TestOperatorSpecGraph.java
index a5b15b8b1e..0cf8b1d382 100644
--- a/samza-core/src/test/java/org/apache/samza/operators/TestOperatorSpecGraph.java
+++ b/samza-core/src/test/java/org/apache/samza/operators/TestOperatorSpecGraph.java
@@ -28,7 +28,7 @@
 import java.util.Set;
 import org.apache.samza.SamzaException;
 import org.apache.samza.application.StreamApplicationDescriptorImpl;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.operators.spec.InputOperatorSpec;
 import org.apache.samza.operators.spec.OperatorSpec;
@@ -177,7 +177,7 @@ public WatermarkFunction getWatermarkFn() {
     }
 
     @Override
-    public TimerFunction getTimerFn() {
+    public SchedulingFunction getSchedulingFn() {
       return null;
     }
   }
diff --git a/samza-core/src/test/java/org/apache/samza/operators/impl/TestOperatorImpl.java b/samza-core/src/test/java/org/apache/samza/operators/impl/TestOperatorImpl.java
index 249ff09f74..91e574ea32 100644
--- a/samza-core/src/test/java/org/apache/samza/operators/impl/TestOperatorImpl.java
+++ b/samza-core/src/test/java/org/apache/samza/operators/impl/TestOperatorImpl.java
@@ -28,7 +28,7 @@
 import org.apache.samza.metrics.MetricsRegistryMap;
 import org.apache.samza.metrics.ReadableMetricsRegistry;
 import org.apache.samza.metrics.Timer;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.operators.spec.OperatorSpec;
 import org.apache.samza.task.MessageCollector;
@@ -220,7 +220,7 @@ public WatermarkFunction getWatermarkFn() {
     }
 
     @Override
-    public TimerFunction getTimerFn() {
+    public SchedulingFunction getSchedulingFn() {
       return null;
     }
   }
diff --git a/samza-core/src/test/java/org/apache/samza/operators/spec/OperatorSpecTestUtils.java b/samza-core/src/test/java/org/apache/samza/operators/spec/OperatorSpecTestUtils.java
index 7704a5b034..9ca3f832af 100644
--- a/samza-core/src/test/java/org/apache/samza/operators/spec/OperatorSpecTestUtils.java
+++ b/samza-core/src/test/java/org/apache/samza/operators/spec/OperatorSpecTestUtils.java
@@ -28,7 +28,7 @@
 import java.util.Map;
 import org.apache.samza.operators.OperatorSpecGraph;
 import org.apache.samza.operators.TableImpl;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.serializers.SerializableSerde;
 import org.apache.samza.table.TableSpec;
@@ -72,7 +72,7 @@ private static void assertClonedOpSpec(OperatorSpec oOpSpec, OperatorSpec nOpSpe
     assertNotEquals(oOpSpec, nOpSpec);
     assertEquals(oOpSpec.getOpId(), nOpSpec.getOpId());
     assertEquals(oOpSpec.getOpCode(), nOpSpec.getOpCode());
-    assertTimerFnsNotEqual(oOpSpec.getTimerFn(), nOpSpec.getTimerFn());
+    assertSchedulingFnsNotEqual(oOpSpec.getSchedulingFn(), nOpSpec.getSchedulingFn());
     assertWatermarkFnNotEqual(nOpSpec.getWatermarkFn(), nOpSpec.getWatermarkFn());
     assertAllOperators(oOpSpec.getRegisteredOperatorSpecs(), nOpSpec.getRegisteredOperatorSpecs());
   }
@@ -84,11 +84,11 @@ private static void assertWatermarkFnNotEqual(WatermarkFunction watermarkFn, Wat
     assertNotEquals(watermarkFn, watermarkFn1);
   }
 
-  private static void assertTimerFnsNotEqual(TimerFunction timerFn, TimerFunction timerFn1) {
-    if (timerFn == timerFn1 && timerFn == null) {
+  private static void assertSchedulingFnsNotEqual(SchedulingFunction schedulingFn, SchedulingFunction schedulingFn1) {
+    if (schedulingFn == schedulingFn1 && schedulingFn == null) {
       return;
     }
-    assertNotEquals(timerFn, timerFn1);
+    assertNotEquals(schedulingFn, schedulingFn1);
   }
 
   private static void assertClonedTables(Map<TableSpec, TableImpl> originalTables, Map<TableSpec, TableImpl> clonedTables) {
diff --git a/samza-core/src/test/java/org/apache/samza/operators/spec/TestOperatorSpec.java b/samza-core/src/test/java/org/apache/samza/operators/spec/TestOperatorSpec.java
index a9ccd12ad6..be851b91b1 100644
--- a/samza-core/src/test/java/org/apache/samza/operators/spec/TestOperatorSpec.java
+++ b/samza-core/src/test/java/org/apache/samza/operators/spec/TestOperatorSpec.java
@@ -24,7 +24,7 @@
 import java.util.List;
 import org.apache.samza.config.MapConfig;
 import org.apache.samza.operators.KV;
-import org.apache.samza.operators.TimerRegistry;
+import org.apache.samza.operators.KeyScheduler;
 import org.apache.samza.operators.data.TestMessageEnvelope;
 import org.apache.samza.operators.data.TestOutputMessageEnvelope;
 import org.apache.samza.operators.functions.FilterFunction;
@@ -33,7 +33,7 @@
 import org.apache.samza.operators.functions.MapFunction;
 import org.apache.samza.operators.functions.SinkFunction;
 import org.apache.samza.operators.functions.StreamTableJoinFunction;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.serializers.JsonSerdeV2;
 import org.apache.samza.serializers.KVSerde;
@@ -74,7 +74,8 @@ public TestOutputMessageEnvelope apply(TestMessageEnvelope m) {
     }
   }
 
-  private static class MapWithTimerFn implements MapFunction<TestMessageEnvelope, TestOutputMessageEnvelope>, TimerFunction<String, TestOutputMessageEnvelope> {
+  private static class MapWithSchedulingFn implements MapFunction<TestMessageEnvelope, TestOutputMessageEnvelope>,
+                                                      SchedulingFunction<String, TestOutputMessageEnvelope> {
 
     @Override
     public TestOutputMessageEnvelope apply(TestMessageEnvelope m) {
@@ -82,12 +83,12 @@ public TestOutputMessageEnvelope apply(TestMessageEnvelope m) {
     }
 
     @Override
-    public void registerTimer(TimerRegistry<String> timerRegistry) {
+    public void schedulingInit(KeyScheduler<String> keyScheduler) {
 
     }
 
     @Override
-    public Collection<TestOutputMessageEnvelope> onTimer(String key, long timestamp) {
+    public Collection<TestOutputMessageEnvelope> executeForKey(String key, long timestamp) {
       return null;
     }
   }
@@ -164,8 +165,8 @@ public void testStreamOperatorSpecWithFlatMap() {
     assertTrue(cloneOperatorSpec.getTransformFn() instanceof FlatMapFunction);
     assertNull(streamOperatorSpec.getWatermarkFn());
     assertNull(cloneOperatorSpec.getWatermarkFn());
-    assertNull(streamOperatorSpec.getTimerFn());
-    assertNull(cloneOperatorSpec.getTimerFn());
+    assertNull(streamOperatorSpec.getSchedulingFn());
+    assertNull(cloneOperatorSpec.getSchedulingFn());
   }
 
   @Test
@@ -187,8 +188,8 @@ public void testStreamOperatorSpecWithMap() {
     assertNotEquals(userFn, clonedUserFn);
     assertNull(streamOperatorSpec.getWatermarkFn());
     assertNull(cloneOperatorSpec.getWatermarkFn());
-    assertNull(streamOperatorSpec.getTimerFn());
-    assertNull(cloneOperatorSpec.getTimerFn());
+    assertNull(streamOperatorSpec.getSchedulingFn());
+    assertNull(cloneOperatorSpec.getSchedulingFn());
   }
 
   @Test
@@ -209,8 +210,8 @@ public void testStreamOperatorSpecWithFilter() {
     assertNotEquals(userFn, clonedUserFn);
     assertNull(streamOperatorSpec.getWatermarkFn());
     assertNull(cloneOperatorSpec.getWatermarkFn());
-    assertNull(streamOperatorSpec.getTimerFn());
-    assertNull(cloneOperatorSpec.getTimerFn());
+    assertNull(streamOperatorSpec.getSchedulingFn());
+    assertNull(cloneOperatorSpec.getSchedulingFn());
   }
 
   @Test
@@ -360,13 +361,13 @@ public void testMapStreamOperatorSpecWithWatermark() {
     assertEquals(streamOperatorSpec.getWatermarkFn(), testMapFn);
     assertNotNull(cloneOperatorSpec.getWatermarkFn());
     assertNotEquals(cloneOperatorSpec.getTransformFn(), cloneOperatorSpec.getWatermarkFn());
-    assertNull(streamOperatorSpec.getTimerFn());
-    assertNull(cloneOperatorSpec.getTimerFn());
+    assertNull(streamOperatorSpec.getSchedulingFn());
+    assertNull(cloneOperatorSpec.getSchedulingFn());
   }
 
   @Test
-  public void testMapStreamOperatorSpecWithTimer() {
-    MapWithTimerFn testMapFn = new MapWithTimerFn();
+  public void testMapStreamOperatorSpecWithSchedulingFunction() {
+    MapWithSchedulingFn testMapFn = new MapWithSchedulingFn();
 
     StreamOperatorSpec<TestMessageEnvelope, TestOutputMessageEnvelope> streamOperatorSpec =
         OperatorSpecs.createMapOperatorSpec(testMapFn, "op0");
@@ -378,9 +379,9 @@ public void testMapStreamOperatorSpecWithTimer() {
     assertNull(streamOperatorSpec.getWatermarkFn());
     assertNull(cloneOperatorSpec.getWatermarkFn());
     assertNotEquals(cloneOperatorSpec.getTransformFn(), cloneOperatorSpec.getWatermarkFn());
-    assertEquals(streamOperatorSpec.getTimerFn(), testMapFn);
-    assertNotNull(cloneOperatorSpec.getTimerFn());
-    assertNotEquals(streamOperatorSpec.getTimerFn(), cloneOperatorSpec.getTimerFn());
+    assertEquals(streamOperatorSpec.getSchedulingFn(), testMapFn);
+    assertNotNull(cloneOperatorSpec.getSchedulingFn());
+    assertNotEquals(streamOperatorSpec.getSchedulingFn(), cloneOperatorSpec.getSchedulingFn());
   }
 
   @Test
diff --git a/samza-core/src/test/java/org/apache/samza/operators/spec/TestPartitionByOperatorSpec.java b/samza-core/src/test/java/org/apache/samza/operators/spec/TestPartitionByOperatorSpec.java
index db7079c8b3..adeeb6df74 100644
--- a/samza-core/src/test/java/org/apache/samza/operators/spec/TestPartitionByOperatorSpec.java
+++ b/samza-core/src/test/java/org/apache/samza/operators/spec/TestPartitionByOperatorSpec.java
@@ -23,13 +23,13 @@
 import org.apache.samza.application.StreamApplicationDescriptorImpl;
 import org.apache.samza.config.Config;
 import org.apache.samza.config.JobConfig;
+import org.apache.samza.operators.KeyScheduler;
 import org.apache.samza.operators.MessageStream;
 import org.apache.samza.operators.OperatorSpecGraph;
-import org.apache.samza.operators.TimerRegistry;
 import org.apache.samza.operators.descriptors.GenericInputDescriptor;
 import org.apache.samza.operators.descriptors.GenericSystemDescriptor;
 import org.apache.samza.operators.functions.MapFunction;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.serializers.KVSerde;
 import org.apache.samza.serializers.NoOpSerde;
@@ -58,7 +58,7 @@ public class TestPartitionByOperatorSpec {
   private final String testJobId = "1";
   private final String testRepartitionedStreamName = "parByKey";
 
-  class TimerMapFn implements MapFunction<Object, String>, TimerFunction<String, Object> {
+  class SchedulingMapFn implements MapFunction<Object, String>, SchedulingFunction<String, Object> {
 
     @Override
     public String apply(Object message) {
@@ -66,12 +66,12 @@ public String apply(Object message) {
     }
 
     @Override
-    public void registerTimer(TimerRegistry<String> timerRegistry) {
+    public void schedulingInit(KeyScheduler<String> keyScheduler) {
 
     }
 
     @Override
-    public Collection<Object> onTimer(String key, long timestamp) {
+    public Collection<Object> executeForKey(String key, long timestamp) {
       return null;
     }
   }
@@ -117,7 +117,7 @@ public void testPartitionBy() {
     assertTrue(inputOpSpec.getKeySerde() instanceof NoOpSerde);
     assertTrue(inputOpSpec.getValueSerde() instanceof NoOpSerde);
     assertTrue(inputOpSpec.isKeyed());
-    assertNull(inputOpSpec.getTimerFn());
+    assertNull(inputOpSpec.getSchedulingFn());
     assertNull(inputOpSpec.getWatermarkFn());
     InputOperatorSpec originInputSpec = inputOpSpecs.get(testinputDescriptor.getStreamId());
     assertTrue(originInputSpec.getRegisteredOperatorSpecs().toArray()[0] instanceof PartitionByOperatorSpec);
@@ -126,7 +126,7 @@ public void testPartitionBy() {
     assertEquals(reparOpSpec.getKeyFunction(), keyFn);
     assertEquals(reparOpSpec.getValueFunction(), valueFn);
     assertEquals(reparOpSpec.getOutputStream().getStreamId(), reparOpSpec.getOpId());
-    assertNull(reparOpSpec.getTimerFn());
+    assertNull(reparOpSpec.getSchedulingFn());
     assertNull(reparOpSpec.getWatermarkFn());
   }
 
@@ -144,7 +144,7 @@ public void testPartitionByWithNoSerde() {
     assertNull(inputOpSpec.getKeySerde());
     assertNull(inputOpSpec.getValueSerde());
     assertTrue(inputOpSpec.isKeyed());
-    assertNull(inputOpSpec.getTimerFn());
+    assertNull(inputOpSpec.getSchedulingFn());
     assertNull(inputOpSpec.getWatermarkFn());
     InputOperatorSpec originInputSpec = streamAppDesc.getInputOperators().get(testinputDescriptor.getStreamId());
     assertTrue(originInputSpec.getRegisteredOperatorSpecs().toArray()[0] instanceof PartitionByOperatorSpec);
@@ -153,7 +153,7 @@ public void testPartitionByWithNoSerde() {
     assertEquals(reparOpSpec.getKeyFunction(), keyFn);
     assertEquals(reparOpSpec.getValueFunction(), valueFn);
     assertEquals(reparOpSpec.getOutputStream().getStreamId(), reparOpSpec.getOpId());
-    assertNull(reparOpSpec.getTimerFn());
+    assertNull(reparOpSpec.getSchedulingFn());
     assertNull(reparOpSpec.getWatermarkFn());
   }
 
@@ -169,8 +169,8 @@ public void testCopy() {
   }
 
   @Test(expected = IllegalArgumentException.class)
-  public void testTimerFunctionAsKeyFn() {
-    TimerMapFn keyFn = new TimerMapFn();
+  public void testSchedulingFunctionAsKeyFn() {
+    SchedulingMapFn keyFn = new SchedulingMapFn();
     new StreamApplicationDescriptorImpl(appDesc -> {
         MessageStream<Object> inputStream = appDesc.getInputStream(testinputDescriptor);
         inputStream.partitionBy(keyFn, m -> m, "parByKey");
@@ -187,8 +187,8 @@ public void testWatermarkFunctionAsKeyFn() {
   }
 
   @Test(expected = IllegalArgumentException.class)
-  public void testTimerFunctionAsValueFn() {
-    TimerMapFn valueFn = new TimerMapFn();
+  public void testSchedulingFunctionAsValueFn() {
+    SchedulingMapFn valueFn = new SchedulingMapFn();
     new StreamApplicationDescriptorImpl(appDesc -> {
         MessageStream<Object> inputStream = appDesc.getInputStream(testinputDescriptor);
         inputStream.partitionBy(m -> m.toString(), valueFn, "parByKey");
diff --git a/samza-core/src/test/java/org/apache/samza/operators/spec/TestWindowOperatorSpec.java b/samza-core/src/test/java/org/apache/samza/operators/spec/TestWindowOperatorSpec.java
index 0a2214bfcf..32fb490157 100644
--- a/samza-core/src/test/java/org/apache/samza/operators/spec/TestWindowOperatorSpec.java
+++ b/samza-core/src/test/java/org/apache/samza/operators/spec/TestWindowOperatorSpec.java
@@ -19,8 +19,8 @@
 
 package org.apache.samza.operators.spec;
 
-import org.apache.samza.operators.TimerRegistry;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.KeyScheduler;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.serializers.Serde;
 import org.apache.samza.operators.functions.FoldLeftFunction;
@@ -90,8 +90,8 @@ public void testTriggerIntervalWithSingleTimeTrigger() {
   }
 
   @Test(expected = IllegalArgumentException.class)
-  public void testIllegalTimerFunctionAsInitializer() {
-    class TimedSupplierFunction implements SupplierFunction<Collection>, TimerFunction<Object, Collection> {
+  public void testIllegalSchedulingFunctionAsInitializer() {
+    class TimedSupplierFunction implements SupplierFunction<Collection>, SchedulingFunction<Object, Collection> {
 
       @Override
       public Collection get() {
@@ -99,12 +99,12 @@ public Collection get() {
       }
 
       @Override
-      public void registerTimer(TimerRegistry<Object> timerRegistry) {
+      public void schedulingInit(KeyScheduler<Object> keyScheduler) {
 
       }
 
       @Override
-      public Collection<Collection> onTimer(Object key, long timestamp) {
+      public Collection<Collection> executeForKey(Object key, long timestamp) {
         return null;
       }
     }
@@ -138,8 +138,8 @@ public Long getOutputWatermark() {
   }
 
   @Test(expected = IllegalArgumentException.class)
-  public void testIllegalTimerFunctionAsKeyFn() {
-    class TimerMapFunction implements MapFunction<Object, Object>, TimerFunction<Object, Object> {
+  public void testIllegalSchedulingFunctionAsKeyFn() {
+    class SchedulingMapFunction implements MapFunction<Object, Object>, SchedulingFunction<Object, Object> {
 
       @Override
       public Object apply(Object message) {
@@ -147,16 +147,16 @@ public Object apply(Object message) {
       }
 
       @Override
-      public void registerTimer(TimerRegistry<Object> timerRegistry) {
+      public void schedulingInit(KeyScheduler<Object> keyScheduler) {
 
       }
 
       @Override
-      public Collection<Object> onTimer(Object key, long timestamp) {
+      public Collection<Object> executeForKey(Object key, long timestamp) {
         return null;
       }
     }
-    keyFn = new TimerMapFunction();
+    keyFn = new SchedulingMapFunction();
 
     getWindowOperatorSpec("w0");
   }
@@ -186,8 +186,8 @@ public Long getOutputWatermark() {
   }
 
   @Test(expected = IllegalArgumentException.class)
-  public void testIllegalTimerFunctionAsEventTimeFn() {
-    class TimerMapFunction implements MapFunction<Object, Long>, TimerFunction<Object, Object> {
+  public void testIllegalSchedulingFunctionAsEventTimeFn() {
+    class SchedulingMapFunction implements MapFunction<Object, Long>, SchedulingFunction<Object, Object> {
 
       @Override
       public Long apply(Object message) {
@@ -195,16 +195,16 @@ public Long apply(Object message) {
       }
 
       @Override
-      public void registerTimer(TimerRegistry<Object> timerRegistry) {
+      public void schedulingInit(KeyScheduler<Object> keyScheduler) {
 
       }
 
       @Override
-      public Collection<Object> onTimer(Object key, long timestamp) {
+      public Collection<Object> executeForKey(Object key, long timestamp) {
         return null;
       }
     }
-    timeFn = new TimerMapFunction();
+    timeFn = new SchedulingMapFunction();
 
     getWindowOperatorSpec("w0");
   }
@@ -234,8 +234,9 @@ public Long getOutputWatermark() {
   }
 
   @Test
-  public void testTimerFunctionAsFoldLeftFn() {
-    class TimerFoldLeftFunction implements FoldLeftFunction<Object, Collection>, TimerFunction<Object, Collection> {
+  public void testSchedulingFunctionAsFoldLeftFn() {
+    class SchedulingFoldLeftFunction
+        implements FoldLeftFunction<Object, Collection>, SchedulingFunction<Object, Collection> {
 
       @Override
       public Collection apply(Object message, Collection oldValue) {
@@ -244,19 +245,19 @@ public Collection apply(Object message, Collection oldValue) {
       }
 
       @Override
-      public void registerTimer(TimerRegistry<Object> timerRegistry) {
+      public void schedulingInit(KeyScheduler<Object> keyScheduler) {
 
       }
 
       @Override
-      public Collection<Collection> onTimer(Object key, long timestamp) {
+      public Collection<Collection> executeForKey(Object key, long timestamp) {
         return null;
       }
     }
 
-    foldFn = new TimerFoldLeftFunction();
+    foldFn = new SchedulingFoldLeftFunction();
     WindowOperatorSpec<Object, Object, Collection> windowSpec = getWindowOperatorSpec("w0");
-    assertEquals(windowSpec.getTimerFn(), foldFn);
+    assertEquals(windowSpec.getSchedulingFn(), foldFn);
     assertNull(windowSpec.getWatermarkFn());
   }
 
@@ -284,7 +285,7 @@ public Collection apply(Object message, Collection oldValue) {
     foldFn = new WatermarkFoldLeftFunction();
     WindowOperatorSpec<Object, Object, Collection> windowSpec = getWindowOperatorSpec("w0");
     assertEquals(windowSpec.getWatermarkFn(), foldFn);
-    assertNull(windowSpec.getTimerFn());
+    assertNull(windowSpec.getSchedulingFn());
   }
 
   @Test
diff --git a/samza-core/src/test/java/org/apache/samza/task/TestSystemTimerScheduler.java b/samza-core/src/test/java/org/apache/samza/task/TestSystemTimerScheduler.java
index dd08121728..038ff27680 100644
--- a/samza-core/src/test/java/org/apache/samza/task/TestSystemTimerScheduler.java
+++ b/samza-core/src/test/java/org/apache/samza/task/TestSystemTimerScheduler.java
@@ -51,7 +51,7 @@ private ScheduledExecutorService createExecutorService() {
 
   private void fireTimers(SystemTimerScheduler factory) {
     factory.removeReadyTimers().entrySet().forEach(entry -> {
-        entry.getValue().onTimer(entry.getKey().getKey(), mock(MessageCollector.class), mock(TaskCoordinator.class));
+        entry.getValue().execute(entry.getKey().getKey(), mock(MessageCollector.class), mock(TaskCoordinator.class));
       });
   }
 
diff --git a/samza-sql/src/test/java/org/apache/samza/sql/translator/TestProjectTranslator.java b/samza-sql/src/test/java/org/apache/samza/sql/translator/TestProjectTranslator.java
index 1acfc4795c..8b17f59a9c 100644
--- a/samza-sql/src/test/java/org/apache/samza/sql/translator/TestProjectTranslator.java
+++ b/samza-sql/src/test/java/org/apache/samza/sql/translator/TestProjectTranslator.java
@@ -39,7 +39,7 @@
 import org.apache.samza.operators.MessageStream;
 import org.apache.samza.operators.MessageStreamImpl;
 import org.apache.samza.operators.functions.MapFunction;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.operators.spec.OperatorSpec;
 import org.apache.samza.operators.spec.StreamOperatorSpec;
@@ -192,7 +192,7 @@ public WatermarkFunction getWatermarkFn() {
       }
 
       @Override
-      public TimerFunction getTimerFn() {
+      public SchedulingFunction getSchedulingFn() {
         return null;
       }
     };
diff --git a/samza-test/src/test/java/org/apache/samza/test/framework/TimerTest.java b/samza-test/src/test/java/org/apache/samza/test/framework/SchedulingTest.java
similarity index 91%
rename from samza-test/src/test/java/org/apache/samza/test/framework/TimerTest.java
rename to samza-test/src/test/java/org/apache/samza/test/framework/SchedulingTest.java
index d4e0e14f02..658492a7a8 100644
--- a/samza-test/src/test/java/org/apache/samza/test/framework/TimerTest.java
+++ b/samza-test/src/test/java/org/apache/samza/test/framework/SchedulingTest.java
@@ -26,9 +26,9 @@
 import org.junit.Before;
 import org.junit.Test;
 
-import static org.apache.samza.test.framework.TestTimerApp.*;
+import static org.apache.samza.test.framework.TestSchedulingApp.*;
 
-public class TimerTest extends StreamApplicationIntegrationTestHarness {
+public class SchedulingTest extends StreamApplicationIntegrationTestHarness {
 
   @Before
   public void setup() {
@@ -55,6 +55,6 @@ public void testJob() throws InterruptedException {
     configs.put(JobCoordinatorConfig.JOB_COORDINATION_UTILS_FACTORY, "org.apache.samza.standalone.PassthroughCoordinationUtilsFactory");
     configs.put(JobConfig.PROCESSOR_ID(), "0");
 
-    runApplication(new TestTimerApp(), "TimerTest", configs);
+    runApplication(new TestSchedulingApp(), "SchedulingTest", configs);
   }
 }
diff --git a/samza-test/src/test/java/org/apache/samza/test/framework/TestTimerApp.java b/samza-test/src/test/java/org/apache/samza/test/framework/TestSchedulingApp.java
similarity index 78%
rename from samza-test/src/test/java/org/apache/samza/test/framework/TestTimerApp.java
rename to samza-test/src/test/java/org/apache/samza/test/framework/TestSchedulingApp.java
index e72a965d26..8a4f2764ff 100644
--- a/samza-test/src/test/java/org/apache/samza/test/framework/TestTimerApp.java
+++ b/samza-test/src/test/java/org/apache/samza/test/framework/TestSchedulingApp.java
@@ -26,16 +26,16 @@
 import java.util.List;
 import org.apache.samza.application.StreamApplication;
 import org.apache.samza.application.StreamApplicationDescriptor;
+import org.apache.samza.operators.KeyScheduler;
 import org.apache.samza.operators.MessageStream;
-import org.apache.samza.operators.TimerRegistry;
 import org.apache.samza.operators.functions.FlatMapFunction;
-import org.apache.samza.operators.functions.TimerFunction;
+import org.apache.samza.operators.functions.SchedulingFunction;
 import org.apache.samza.serializers.JsonSerdeV2;
 import org.apache.samza.system.kafka.KafkaInputDescriptor;
 import org.apache.samza.system.kafka.KafkaSystemDescriptor;
 import org.apache.samza.test.operator.data.PageView;
 
-public class TestTimerApp implements StreamApplication {
+public class TestSchedulingApp implements StreamApplication {
   public static final String PAGE_VIEWS = "page-views";
 
   @Override
@@ -44,9 +44,9 @@ public void describe(StreamApplicationDescriptor appDesc) {
     KafkaSystemDescriptor ksd = new KafkaSystemDescriptor("kafka");
     KafkaInputDescriptor<PageView> isd = ksd.getInputDescriptor(PAGE_VIEWS, serde);
     final MessageStream<PageView> pageViews = appDesc.getInputStream(isd);
-    final MessageStream<PageView> output = pageViews.flatMap(new FlatmapTimerFn());
+    final MessageStream<PageView> output = pageViews.flatMap(new FlatmapSchedulingFn());
 
-    MessageStreamAssert.that("Output from timer function should container all complete messages", output, serde)
+    MessageStreamAssert.that("Output from scheduling function should container all complete messages", output, serde)
         .containsInAnyOrder(
             Arrays.asList(
                 new PageView("v1-complete", "p1", "u1"),
@@ -56,14 +56,15 @@ public void describe(StreamApplicationDescriptor appDesc) {
             ));
   }
 
-  private static class FlatmapTimerFn implements FlatMapFunction<PageView, PageView>, TimerFunction<String, PageView> {
+  private static class FlatmapSchedulingFn
+      implements FlatMapFunction<PageView, PageView>, SchedulingFunction<String, PageView> {
 
     private transient List<PageView> pageViews;
-    private transient TimerRegistry<String> timerRegistry;
+    private transient KeyScheduler<String> keyScheduler;
 
     @Override
-    public void registerTimer(TimerRegistry<String> timerRegistry) {
-      this.timerRegistry = timerRegistry;
+    public void schedulingInit(KeyScheduler<String> keyScheduler) {
+      this.keyScheduler = keyScheduler;
       this.pageViews = new ArrayList<>();
     }
 
@@ -75,13 +76,13 @@ public Collection<PageView> apply(PageView message) {
       if (pageViews.size() == 2) {
         //got all messages for this task
         final long time = System.currentTimeMillis() + 100;
-        timerRegistry.register("CompleteTimer", time);
+        keyScheduler.schedule("CompleteScheduler", time);
       }
       return Collections.emptyList();
     }
 
     @Override
-    public Collection<PageView> onTimer(String key, long time) {
+    public Collection<PageView> executeForKey(String key, long time) {
       return pageViews;
     }
   }

From db4fad6debe101f5103537f7c942011505ea2829 Mon Sep 17 00:00:00 2001
From: Cameron Lee <calee@linkedin.com>
Date: Mon, 17 Sep 2018 17:46:18 -0700
Subject: [PATCH 2/4] minor style check update

---
 .../main/java/org/apache/samza/operators/KeyScheduler.java  | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/samza-api/src/main/java/org/apache/samza/operators/KeyScheduler.java b/samza-api/src/main/java/org/apache/samza/operators/KeyScheduler.java
index 22e87d5e6d..be8dae2b79 100644
--- a/samza-api/src/main/java/org/apache/samza/operators/KeyScheduler.java
+++ b/samza-api/src/main/java/org/apache/samza/operators/KeyScheduler.java
@@ -19,11 +19,9 @@
 
 package org.apache.samza.operators;
 
-import org.apache.samza.operators.functions.SchedulingFunction;
-
-
 /**
- * Manages scheduling keys to be triggered later. See {@link SchedulingFunction} for details.
+ * Manages scheduling keys to be triggered later. See {@link org.apache.samza.operators.functions.SchedulingFunction}
+ * for details.
  * @param <K> type of the key
  */
 public interface KeyScheduler<K> {

From b63e032c2cbb8e1eadbc7bd6acb30bd431272d54 Mon Sep 17 00:00:00 2001
From: Cameron Lee <calee@linkedin.com>
Date: Tue, 18 Sep 2018 13:44:29 -0700
Subject: [PATCH 3/4] simplify terminology: rename Scheduling to Scheduled,
 rename KeyScheduler to Scheduler

---
 .../{KeyScheduler.java => Scheduler.java}     |  4 +-
 ...ngFunction.java => ScheduledFunction.java} | 23 ++++-----
 ...ngCallback.java => ScheduledCallback.java} |  4 +-
 .../org/apache/samza/task/TaskContext.java    |  4 +-
 .../samza/container/TaskContextImpl.java      |  4 +-
 .../samza/operators/impl/OperatorImpl.java    | 20 ++++----
 .../operators/impl/OperatorImplGraph.java     |  8 ++--
 .../operators/spec/BroadcastOperatorSpec.java |  4 +-
 .../operators/spec/FilterOperatorSpec.java    |  6 +--
 .../operators/spec/FlatMapOperatorSpec.java   |  6 +--
 .../operators/spec/InputOperatorSpec.java     |  4 +-
 .../operators/spec/JoinOperatorSpec.java      |  6 +--
 .../samza/operators/spec/MapOperatorSpec.java |  6 +--
 .../operators/spec/MergeOperatorSpec.java     |  4 +-
 .../samza/operators/spec/OperatorSpec.java    |  4 +-
 .../operators/spec/OutputOperatorSpec.java    |  4 +-
 .../spec/PartitionByOperatorSpec.java         | 12 ++---
 .../spec/SendToTableOperatorSpec.java         |  4 +-
 .../operators/spec/SinkOperatorSpec.java      |  6 +--
 .../spec/StreamTableJoinOperatorSpec.java     |  6 +--
 .../operators/spec/WindowOperatorSpec.java    | 18 +++----
 .../samza/task/SystemTimerScheduler.java      | 10 ++--
 .../apache/samza/container/TaskInstance.scala |  4 +-
 .../operators/TestOperatorSpecGraph.java      |  4 +-
 .../operators/impl/TestOperatorImpl.java      |  4 +-
 .../operators/spec/OperatorSpecTestUtils.java | 10 ++--
 .../operators/spec/TestOperatorSpec.java      | 38 +++++++--------
 .../spec/TestPartitionByOperatorSpec.java     | 26 +++++-----
 .../spec/TestWindowOperatorSpec.java          | 48 +++++++++----------
 .../samza/task/TestSystemTimerScheduler.java  |  2 +-
 .../sql/translator/TestProjectTranslator.java |  4 +-
 .../test/framework/TestSchedulingApp.java     | 20 ++++----
 32 files changed, 164 insertions(+), 163 deletions(-)
 rename samza-api/src/main/java/org/apache/samza/operators/{KeyScheduler.java => Scheduler.java} (93%)
 rename samza-api/src/main/java/org/apache/samza/operators/functions/{SchedulingFunction.java => ScheduledFunction.java} (72%)
 rename samza-api/src/main/java/org/apache/samza/scheduler/{SchedulingCallback.java => ScheduledCallback.java} (91%)

diff --git a/samza-api/src/main/java/org/apache/samza/operators/KeyScheduler.java b/samza-api/src/main/java/org/apache/samza/operators/Scheduler.java
similarity index 93%
rename from samza-api/src/main/java/org/apache/samza/operators/KeyScheduler.java
rename to samza-api/src/main/java/org/apache/samza/operators/Scheduler.java
index be8dae2b79..05bea38bca 100644
--- a/samza-api/src/main/java/org/apache/samza/operators/KeyScheduler.java
+++ b/samza-api/src/main/java/org/apache/samza/operators/Scheduler.java
@@ -20,11 +20,11 @@
 package org.apache.samza.operators;
 
 /**
- * Manages scheduling keys to be triggered later. See {@link org.apache.samza.operators.functions.SchedulingFunction}
+ * Manages scheduling keys to be triggered later. See {@link org.apache.samza.operators.functions.ScheduledFunction}
  * for details.
  * @param <K> type of the key
  */
-public interface KeyScheduler<K> {
+public interface Scheduler<K> {
 
   /**
    * Schedule a key to be triggered at {@code timestamp}.
diff --git a/samza-api/src/main/java/org/apache/samza/operators/functions/SchedulingFunction.java b/samza-api/src/main/java/org/apache/samza/operators/functions/ScheduledFunction.java
similarity index 72%
rename from samza-api/src/main/java/org/apache/samza/operators/functions/SchedulingFunction.java
rename to samza-api/src/main/java/org/apache/samza/operators/functions/ScheduledFunction.java
index 21cb0895b7..b75b335a07 100644
--- a/samza-api/src/main/java/org/apache/samza/operators/functions/SchedulingFunction.java
+++ b/samza-api/src/main/java/org/apache/samza/operators/functions/ScheduledFunction.java
@@ -19,27 +19,28 @@
 
 package org.apache.samza.operators.functions;
 
-import org.apache.samza.operators.KeyScheduler;
+import org.apache.samza.operators.Scheduler;
 
 import java.util.Collection;
 
+
 /**
  * Allows scheduling with key(s) and is invoked when the specified time(s) occurs.
  * Key must be a unique identifier for its corresponding logic to execute, and is provided in the callback when the
  * corresponding schedule time occurs.
  *
  * <p>
- * Example of a {@link FlatMapFunction} with {@link SchedulingFunction}:
+ * Example of a {@link FlatMapFunction} with {@link ScheduledFunction}:
  * <pre>{@code
- *    public class ExampleSchedulingFn implements FlatMapFunction<String, String>, SchedulingFunction<String, String> {
- *      public void schedulingInit(KeyScheduler keyScheduler) {
+ *    public class ExampleScheduledFn implements FlatMapFunction<String, String>, ScheduledFunction<String, String> {
+ *      public void schedule(Scheduler scheduler) {
  *        long time = System.currentTimeMillis() + 5000; // fire after 5 sec
- *        keyScheduler.schedule("example-scheduler-logic", time);
+ *        scheduler.schedule("example-scheduler-logic", time);
  *      }
  *      public Collection<String> apply(String s) {
  *        ...
  *      }
- *      public Collection<String> executeForKey(String key, long timestamp) {
+ *      public Collection<String> onCallback(String key, long timestamp) {
  *        // fired with key as "example-scheduler-logic"
  *        ...
  *      }
@@ -48,14 +49,14 @@
  * @param <K> type of the key
  * @param <OM> type of the output
  */
-public interface SchedulingFunction<K, OM> {
+public interface ScheduledFunction<K, OM> {
 
   /**
    * Initialize the function for scheduling, such as setting some initial scheduling logic or saving the
-   * {@code keyScheduler} for later use.
-   * @param keyScheduler used to specify the schedule time(s) and key(s)
+   * {@code scheduler} for later use.
+   * @param scheduler used to specify the schedule time(s) and key(s)
    */
-  void schedulingInit(KeyScheduler<K> keyScheduler);
+  void schedule(Scheduler<K> scheduler);
 
   /**
    * Returns the output from the scheduling logic corresponding to the key that was triggered.
@@ -63,5 +64,5 @@ public interface SchedulingFunction<K, OM> {
    * @param timestamp schedule time that was set for the key, in milliseconds since epoch
    * @return {@link Collection} of output elements
    */
-  Collection<OM> executeForKey(K key, long timestamp);
+  Collection<OM> onCallback(K key, long timestamp);
 }
diff --git a/samza-api/src/main/java/org/apache/samza/scheduler/SchedulingCallback.java b/samza-api/src/main/java/org/apache/samza/scheduler/ScheduledCallback.java
similarity index 91%
rename from samza-api/src/main/java/org/apache/samza/scheduler/SchedulingCallback.java
rename to samza-api/src/main/java/org/apache/samza/scheduler/ScheduledCallback.java
index 34a5341f0e..87454228a5 100644
--- a/samza-api/src/main/java/org/apache/samza/scheduler/SchedulingCallback.java
+++ b/samza-api/src/main/java/org/apache/samza/scheduler/ScheduledCallback.java
@@ -28,12 +28,12 @@
  * {@link org.apache.samza.task.TaskContext} is reached.
  * @param <K> type of the callback key
  */
-public interface SchedulingCallback<K> {
+public interface ScheduledCallback<K> {
   /**
    * Invoked when the corresponding schedule time is reached.
    * @param key key for callback
    * @param collector contains the means of sending message envelopes to the output stream.
    * @param coordinator manages execution of tasks.
    */
-  void execute(K key, MessageCollector collector, TaskCoordinator coordinator);
+  void onCallback(K key, MessageCollector collector, TaskCoordinator coordinator);
 }
diff --git a/samza-api/src/main/java/org/apache/samza/task/TaskContext.java b/samza-api/src/main/java/org/apache/samza/task/TaskContext.java
index 32b9be3aa6..f142d5ca8f 100644
--- a/samza-api/src/main/java/org/apache/samza/task/TaskContext.java
+++ b/samza-api/src/main/java/org/apache/samza/task/TaskContext.java
@@ -24,7 +24,7 @@
 import org.apache.samza.container.SamzaContainerContext;
 import org.apache.samza.container.TaskName;
 import org.apache.samza.metrics.MetricsRegistry;
-import org.apache.samza.scheduler.SchedulingCallback;
+import org.apache.samza.scheduler.ScheduledCallback;
 import org.apache.samza.system.SystemStreamPartition;
 import org.apache.samza.table.Table;
 
@@ -85,7 +85,7 @@ default Object getUserContext() {
    * @param callback callback to call when the {@code timestamp} is reached
    * @param <K> type of the key
    */
-  <K> void scheduleCallback(K key, long timestamp, SchedulingCallback<K> callback);
+  <K> void scheduleCallback(K key, long timestamp, ScheduledCallback<K> callback);
 
   /**
    * Delete the keyed callback in this task.
diff --git a/samza-core/src/main/java/org/apache/samza/container/TaskContextImpl.java b/samza-core/src/main/java/org/apache/samza/container/TaskContextImpl.java
index 05f849099d..f1d265a72a 100644
--- a/samza-core/src/main/java/org/apache/samza/container/TaskContextImpl.java
+++ b/samza-core/src/main/java/org/apache/samza/container/TaskContextImpl.java
@@ -31,7 +31,7 @@
 import org.apache.samza.table.TableManager;
 import org.apache.samza.task.SystemTimerScheduler;
 import org.apache.samza.task.TaskContext;
-import org.apache.samza.scheduler.SchedulingCallback;
+import org.apache.samza.scheduler.ScheduledCallback;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -134,7 +134,7 @@ public Object getUserContext() {
   }
 
   @Override
-  public <K> void scheduleCallback(K key, long timestamp, SchedulingCallback<K> callback) {
+  public <K> void scheduleCallback(K key, long timestamp, ScheduledCallback<K> callback) {
     timerScheduler.setTimer(key, timestamp, callback);
   }
 
diff --git a/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImpl.java b/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImpl.java
index 851b48f012..64db79150a 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImpl.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImpl.java
@@ -25,8 +25,8 @@
 import org.apache.samza.container.TaskName;
 import org.apache.samza.job.model.ContainerModel;
 import org.apache.samza.job.model.TaskModel;
-import org.apache.samza.operators.KeyScheduler;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.Scheduler;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.system.EndOfStreamMessage;
 import org.apache.samza.metrics.Counter;
@@ -436,19 +436,19 @@ final long getOutputWatermark() {
 
   /**
    * Returns a registry which allows registering arbitrary system-clock timer with K-typed key.
-   * The user-defined function in the operator spec needs to implement {@link SchedulingFunction#executeForKey(Object, long)}
+   * The user-defined function in the operator spec needs to implement {@link ScheduledFunction#onCallback(Object, long)}
    * for timer notifications.
    * @param <K> key type for the timer.
-   * @return an instance of {@link KeyScheduler}
+   * @return an instance of {@link Scheduler}
    */
-  <K> KeyScheduler<K> createOperatorKeyScheduler() {
-    return new KeyScheduler<K>() {
+  <K> Scheduler<K> createOperatorScheduler() {
+    return new Scheduler<K>() {
       @Override
       public void schedule(K key, long time) {
         taskContext.scheduleCallback(key, time, (k, collector, coordinator) -> {
-            final SchedulingFunction<K, RM> schedulingFn = getOperatorSpec().getSchedulingFn();
-            if (schedulingFn != null) {
-              final Collection<RM> output = schedulingFn.executeForKey(key, time);
+            final ScheduledFunction<K, RM> scheduledFn = getOperatorSpec().getScheduledFn();
+            if (scheduledFn != null) {
+              final Collection<RM> output = scheduledFn.onCallback(key, time);
 
               if (!output.isEmpty()) {
                 output.forEach(rm ->
@@ -457,7 +457,7 @@ public void schedule(K key, long time) {
               }
             } else {
               throw new SamzaException(
-                  String.format("Operator %s id %s (created at %s) must implement SchedulingFunction to use system timer.",
+                  String.format("Operator %s id %s (created at %s) must implement ScheduledFunction to use system timer.",
                       getOperatorSpec().getOpCode().name(), getOpImplId(), getOperatorSpec().getSourceLocation()));
             }
           });
diff --git a/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImplGraph.java b/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImplGraph.java
index 13b1fc593e..6c78ae4e51 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImplGraph.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImplGraph.java
@@ -26,7 +26,7 @@
 import org.apache.samza.container.TaskContextImpl;
 import org.apache.samza.job.model.JobModel;
 import org.apache.samza.operators.KV;
-import org.apache.samza.operators.KeyScheduler;
+import org.apache.samza.operators.Scheduler;
 import org.apache.samza.operators.functions.JoinFunction;
 import org.apache.samza.operators.functions.PartialJoinFunction;
 import org.apache.samza.util.TimestampedValue;
@@ -170,9 +170,9 @@ private OperatorImpl createAndRegisterOperatorImpl(OperatorSpec prevOperatorSpec
       operatorImpl.init(config, context);
       operatorImpl.registerInputStream(inputStream);
 
-      if (operatorSpec.getSchedulingFn() != null) {
-        final KeyScheduler keyScheduler = operatorImpl.createOperatorKeyScheduler();
-        operatorSpec.getSchedulingFn().schedulingInit(keyScheduler);
+      if (operatorSpec.getScheduledFn() != null) {
+        final Scheduler scheduler = operatorImpl.createOperatorScheduler();
+        operatorSpec.getScheduledFn().schedule(scheduler);
       }
 
       // Note: The key here is opImplId, which may not equal opId for some impls (e.g. PartialJoinOperatorImpl).
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/BroadcastOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/BroadcastOperatorSpec.java
index abc9bee0c7..fb6515aa76 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/BroadcastOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/BroadcastOperatorSpec.java
@@ -20,7 +20,7 @@
 
 package org.apache.samza.operators.spec;
 
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 
 public class BroadcastOperatorSpec<M> extends OperatorSpec<M, Void> {
@@ -43,7 +43,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public SchedulingFunction getSchedulingFn() {
+  public ScheduledFunction getScheduledFn() {
     return null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/FilterOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/FilterOperatorSpec.java
index b26f914ee6..4e640dcf0f 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/FilterOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/FilterOperatorSpec.java
@@ -23,7 +23,7 @@
 import org.apache.samza.config.Config;
 import org.apache.samza.operators.functions.FilterFunction;
 import org.apache.samza.operators.functions.FlatMapFunction;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.task.TaskContext;
 
@@ -68,7 +68,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public SchedulingFunction getSchedulingFn() {
-    return this.filterFn instanceof SchedulingFunction ? (SchedulingFunction) this.filterFn : null;
+  public ScheduledFunction getScheduledFn() {
+    return this.filterFn instanceof ScheduledFunction ? (ScheduledFunction) this.filterFn : null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/FlatMapOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/FlatMapOperatorSpec.java
index d52dc0ff2a..160f432da1 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/FlatMapOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/FlatMapOperatorSpec.java
@@ -19,7 +19,7 @@
 package org.apache.samza.operators.spec;
 
 import org.apache.samza.operators.functions.FlatMapFunction;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 
 
@@ -41,7 +41,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public SchedulingFunction getSchedulingFn() {
-    return this.transformFn instanceof SchedulingFunction ? (SchedulingFunction) this.transformFn : null;
+  public ScheduledFunction getScheduledFn() {
+    return this.transformFn instanceof ScheduledFunction ? (ScheduledFunction) this.transformFn : null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/InputOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/InputOperatorSpec.java
index afb8266994..1af4806dd7 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/InputOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/InputOperatorSpec.java
@@ -19,7 +19,7 @@
 package org.apache.samza.operators.spec;
 
 import org.apache.samza.operators.functions.InputTransformer;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.serializers.Serde;
 import org.apache.samza.system.IncomingMessageEnvelope;
@@ -99,7 +99,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public SchedulingFunction getSchedulingFn() {
+  public ScheduledFunction getScheduledFn() {
     return null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/JoinOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/JoinOperatorSpec.java
index 5bb64e44ce..bb6ed59c5c 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/JoinOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/JoinOperatorSpec.java
@@ -20,7 +20,7 @@
 
 import com.google.common.collect.ImmutableMap;
 import org.apache.samza.operators.functions.JoinFunction;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.operators.impl.store.TimestampedValueSerde;
 import org.apache.samza.util.TimestampedValue;
@@ -105,8 +105,8 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public SchedulingFunction getSchedulingFn() {
-    return joinFn instanceof SchedulingFunction ? (SchedulingFunction) joinFn : null;
+  public ScheduledFunction getScheduledFn() {
+    return joinFn instanceof ScheduledFunction ? (ScheduledFunction) joinFn : null;
   }
 
   public OperatorSpec getLeftInputOpSpec() {
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/MapOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/MapOperatorSpec.java
index 36a55422fc..6ce522f687 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/MapOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/MapOperatorSpec.java
@@ -23,7 +23,7 @@
 import org.apache.samza.config.Config;
 import org.apache.samza.operators.functions.FlatMapFunction;
 import org.apache.samza.operators.functions.MapFunction;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.task.TaskContext;
 
@@ -71,7 +71,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public SchedulingFunction getSchedulingFn() {
-    return this.mapFn instanceof SchedulingFunction ? (SchedulingFunction) this.mapFn : null;
+  public ScheduledFunction getScheduledFn() {
+    return this.mapFn instanceof ScheduledFunction ? (ScheduledFunction) this.mapFn : null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/MergeOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/MergeOperatorSpec.java
index 18dd15ea36..3685c5f02a 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/MergeOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/MergeOperatorSpec.java
@@ -19,7 +19,7 @@
 package org.apache.samza.operators.spec;
 
 import java.util.ArrayList;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 
 
@@ -45,7 +45,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public SchedulingFunction getSchedulingFn() {
+  public ScheduledFunction getScheduledFn() {
     return null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/OperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/OperatorSpec.java
index 6cd16cf17c..0442f7c8b7 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/OperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/OperatorSpec.java
@@ -25,7 +25,7 @@
 import org.apache.samza.annotation.InterfaceStability;
 import org.apache.samza.operators.MessageStream;
 import org.apache.samza.operators.MessageStreamImpl;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 
 /**
@@ -143,5 +143,5 @@ public final String getSourceLocation() {
 
   abstract public WatermarkFunction getWatermarkFn();
 
-  abstract public SchedulingFunction getSchedulingFn();
+  abstract public ScheduledFunction getScheduledFn();
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/OutputOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/OutputOperatorSpec.java
index 3487b1a8f8..d6238b8fcf 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/OutputOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/OutputOperatorSpec.java
@@ -19,7 +19,7 @@
 package org.apache.samza.operators.spec;
 
 
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 
 /**
@@ -59,7 +59,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public SchedulingFunction getSchedulingFn() {
+  public ScheduledFunction getScheduledFn() {
     return null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/PartitionByOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/PartitionByOperatorSpec.java
index dee72e392e..069c8673be 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/PartitionByOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/PartitionByOperatorSpec.java
@@ -20,7 +20,7 @@
 
 import org.apache.samza.operators.KV;
 import org.apache.samza.operators.functions.MapFunction;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 
 import static com.google.common.base.Preconditions.checkArgument;
@@ -55,10 +55,10 @@ public class PartitionByOperatorSpec<M, K, V> extends OperatorSpec<M, Void> {
       MapFunction<? super M, ? extends K> keyFunction,
       MapFunction<? super M, ? extends V> valueFunction, String opId) {
     super(OpCode.PARTITION_BY, opId);
-    checkArgument(!(keyFunction instanceof SchedulingFunction || keyFunction instanceof WatermarkFunction),
-        "keyFunction for partitionBy should not implement SchedulingFunction or WatermarkFunction.");
-    checkArgument(!(valueFunction instanceof SchedulingFunction || valueFunction instanceof WatermarkFunction),
-        "valueFunction for partitionBy should not implement SchedulingFunction or WatermarkFunction.");
+    checkArgument(!(keyFunction instanceof ScheduledFunction || keyFunction instanceof WatermarkFunction),
+        "keyFunction for partitionBy should not implement ScheduledFunction or WatermarkFunction.");
+    checkArgument(!(valueFunction instanceof ScheduledFunction || valueFunction instanceof WatermarkFunction),
+        "valueFunction for partitionBy should not implement ScheduledFunction or WatermarkFunction.");
     this.outputStream = outputStream;
     this.keyFunction = keyFunction;
     this.valueFunction = valueFunction;
@@ -86,7 +86,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public SchedulingFunction getSchedulingFn() {
+  public ScheduledFunction getScheduledFn() {
     return null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/SendToTableOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/SendToTableOperatorSpec.java
index 5a11a66ec0..bf032a2f46 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/SendToTableOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/SendToTableOperatorSpec.java
@@ -20,7 +20,7 @@
 
 import org.apache.samza.annotation.InterfaceStability;
 import org.apache.samza.operators.KV;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.table.TableSpec;
 
@@ -58,7 +58,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public SchedulingFunction getSchedulingFn() {
+  public ScheduledFunction getScheduledFn() {
     return null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/SinkOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/SinkOperatorSpec.java
index b27f8a8351..91e2775eb4 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/SinkOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/SinkOperatorSpec.java
@@ -19,7 +19,7 @@
 package org.apache.samza.operators.spec;
 
 import org.apache.samza.operators.functions.SinkFunction;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 
 
@@ -57,7 +57,7 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public SchedulingFunction getSchedulingFn() {
-    return sinkFn instanceof SchedulingFunction ? (SchedulingFunction) sinkFn : null;
+  public ScheduledFunction getScheduledFn() {
+    return sinkFn instanceof ScheduledFunction ? (ScheduledFunction) sinkFn : null;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/StreamTableJoinOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/StreamTableJoinOperatorSpec.java
index 28018d32f7..1849c640a6 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/StreamTableJoinOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/StreamTableJoinOperatorSpec.java
@@ -19,7 +19,7 @@
 package org.apache.samza.operators.spec;
 
 import org.apache.samza.annotation.InterfaceStability;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.StreamTableJoinFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.table.TableSpec;
@@ -66,8 +66,8 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public SchedulingFunction getSchedulingFn() {
-    return joinFn instanceof SchedulingFunction ? (SchedulingFunction) joinFn : null;
+  public ScheduledFunction getScheduledFn() {
+    return joinFn instanceof ScheduledFunction ? (ScheduledFunction) joinFn : null;
   }
 
 }
diff --git a/samza-core/src/main/java/org/apache/samza/operators/spec/WindowOperatorSpec.java b/samza-core/src/main/java/org/apache/samza/operators/spec/WindowOperatorSpec.java
index f4a074a224..ede16a5594 100644
--- a/samza-core/src/main/java/org/apache/samza/operators/spec/WindowOperatorSpec.java
+++ b/samza-core/src/main/java/org/apache/samza/operators/spec/WindowOperatorSpec.java
@@ -20,7 +20,7 @@
 package org.apache.samza.operators.spec;
 
 import org.apache.samza.operators.functions.FoldLeftFunction;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.operators.impl.store.TimeSeriesKeySerde;
 import org.apache.samza.operators.triggers.AnyTrigger;
@@ -64,14 +64,14 @@ public class WindowOperatorSpec<M, WK, WV> extends OperatorSpec<M, WindowPane<WK
   WindowOperatorSpec(WindowInternal<M, WK, WV> window, String opId) {
     super(OpCode.WINDOW, opId);
     checkArgument(window.getInitializer() == null ||
-        !(window.getInitializer() instanceof SchedulingFunction || window.getInitializer() instanceof WatermarkFunction),
-        "A window does not accepts a user-defined SchedulingFunction or WatermarkFunction as the initializer.");
+        !(window.getInitializer() instanceof ScheduledFunction || window.getInitializer() instanceof WatermarkFunction),
+        "A window does not accepts a user-defined ScheduledFunction or WatermarkFunction as the initializer.");
     checkArgument(window.getKeyExtractor() == null ||
-        !(window.getKeyExtractor() instanceof SchedulingFunction || window.getKeyExtractor() instanceof WatermarkFunction),
-        "A window does not accepts a user-defined SchedulingFunction or WatermarkFunction as the keyExtractor.");
+        !(window.getKeyExtractor() instanceof ScheduledFunction || window.getKeyExtractor() instanceof WatermarkFunction),
+        "A window does not accepts a user-defined ScheduledFunction or WatermarkFunction as the keyExtractor.");
     checkArgument(window.getEventTimeExtractor() == null ||
-        !(window.getEventTimeExtractor() instanceof SchedulingFunction || window.getEventTimeExtractor() instanceof WatermarkFunction),
-        "A window does not accepts a user-defined SchedulingFunction or WatermarkFunction as the eventTimeExtractor.");
+        !(window.getEventTimeExtractor() instanceof ScheduledFunction || window.getEventTimeExtractor() instanceof WatermarkFunction),
+        "A window does not accepts a user-defined ScheduledFunction or WatermarkFunction as the eventTimeExtractor.");
     this.window = window;
   }
 
@@ -135,9 +135,9 @@ public WatermarkFunction getWatermarkFn() {
   }
 
   @Override
-  public SchedulingFunction getSchedulingFn() {
+  public ScheduledFunction getScheduledFn() {
     FoldLeftFunction fn = window.getFoldLeftFunction();
-    return fn instanceof SchedulingFunction ? (SchedulingFunction) fn : null;
+    return fn instanceof ScheduledFunction ? (ScheduledFunction) fn : null;
   }
 
   @Override
diff --git a/samza-core/src/main/java/org/apache/samza/task/SystemTimerScheduler.java b/samza-core/src/main/java/org/apache/samza/task/SystemTimerScheduler.java
index eba9e583e6..f89175e190 100644
--- a/samza-core/src/main/java/org/apache/samza/task/SystemTimerScheduler.java
+++ b/samza-core/src/main/java/org/apache/samza/task/SystemTimerScheduler.java
@@ -25,7 +25,7 @@
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
-import org.apache.samza.scheduler.SchedulingCallback;
+import org.apache.samza.scheduler.ScheduledCallback;
 
 import static com.google.common.base.Preconditions.checkState;
 
@@ -47,7 +47,7 @@ public interface TimerListener {
 
   private final ScheduledExecutorService executor;
   private final Map<Object, ScheduledFuture> scheduledFutures = new ConcurrentHashMap<>();
-  private final Map<TimerKey<?>, SchedulingCallback> readyTimers = new ConcurrentHashMap<>();
+  private final Map<TimerKey<?>, ScheduledCallback> readyTimers = new ConcurrentHashMap<>();
   private TimerListener timerListener;
 
   public static SystemTimerScheduler create(ScheduledExecutorService executor) {
@@ -58,7 +58,7 @@ private SystemTimerScheduler(ScheduledExecutorService executor) {
     this.executor = executor;
   }
 
-  public <K> void setTimer(K key, long timestamp, SchedulingCallback<K> callback) {
+  public <K> void setTimer(K key, long timestamp, ScheduledCallback<K> callback) {
     checkState(!scheduledFutures.containsKey(key),
         String.format("Duplicate key %s registration for the same timer", key));
 
@@ -85,8 +85,8 @@ void registerListener(TimerListener listener) {
     timerListener = listener;
   }
 
-  public Map<TimerKey<?>, SchedulingCallback> removeReadyTimers() {
-    final Map<TimerKey<?>, SchedulingCallback> timers = new TreeMap<>(readyTimers);
+  public Map<TimerKey<?>, ScheduledCallback> removeReadyTimers() {
+    final Map<TimerKey<?>, ScheduledCallback> timers = new TreeMap<>(readyTimers);
     readyTimers.keySet().removeAll(timers.keySet());
     return timers;
   }
diff --git a/samza-core/src/main/scala/org/apache/samza/container/TaskInstance.scala b/samza-core/src/main/scala/org/apache/samza/container/TaskInstance.scala
index a3448fcece..9f4fd1716f 100644
--- a/samza-core/src/main/scala/org/apache/samza/container/TaskInstance.scala
+++ b/samza-core/src/main/scala/org/apache/samza/container/TaskInstance.scala
@@ -28,7 +28,7 @@ import org.apache.samza.config.Config
 import org.apache.samza.config.StreamConfig.Config2Stream
 import org.apache.samza.job.model.JobModel
 import org.apache.samza.metrics.MetricsReporter
-import org.apache.samza.scheduler.SchedulingCallback
+import org.apache.samza.scheduler.ScheduledCallback
 import org.apache.samza.storage.kv.KeyValueStore
 import org.apache.samza.storage.{TaskSideInputStorageManager, TaskStorageManager}
 import org.apache.samza.system._
@@ -227,7 +227,7 @@ class TaskInstance(
 
     exceptionHandler.maybeHandle {
       context.getTimerScheduler.removeReadyTimers().entrySet().foreach { entry =>
-        entry.getValue.asInstanceOf[SchedulingCallback[Any]].execute(entry.getKey.getKey, collector, coordinator)
+        entry.getValue.asInstanceOf[ScheduledCallback[Any]].onCallback(entry.getKey.getKey, collector, coordinator)
       }
     }
   }
diff --git a/samza-core/src/test/java/org/apache/samza/operators/TestOperatorSpecGraph.java b/samza-core/src/test/java/org/apache/samza/operators/TestOperatorSpecGraph.java
index 0cf8b1d382..71f4b733b5 100644
--- a/samza-core/src/test/java/org/apache/samza/operators/TestOperatorSpecGraph.java
+++ b/samza-core/src/test/java/org/apache/samza/operators/TestOperatorSpecGraph.java
@@ -28,7 +28,7 @@
 import java.util.Set;
 import org.apache.samza.SamzaException;
 import org.apache.samza.application.StreamApplicationDescriptorImpl;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.operators.spec.InputOperatorSpec;
 import org.apache.samza.operators.spec.OperatorSpec;
@@ -177,7 +177,7 @@ public WatermarkFunction getWatermarkFn() {
     }
 
     @Override
-    public SchedulingFunction getSchedulingFn() {
+    public ScheduledFunction getScheduledFn() {
       return null;
     }
   }
diff --git a/samza-core/src/test/java/org/apache/samza/operators/impl/TestOperatorImpl.java b/samza-core/src/test/java/org/apache/samza/operators/impl/TestOperatorImpl.java
index 91e574ea32..6d12d99497 100644
--- a/samza-core/src/test/java/org/apache/samza/operators/impl/TestOperatorImpl.java
+++ b/samza-core/src/test/java/org/apache/samza/operators/impl/TestOperatorImpl.java
@@ -28,7 +28,7 @@
 import org.apache.samza.metrics.MetricsRegistryMap;
 import org.apache.samza.metrics.ReadableMetricsRegistry;
 import org.apache.samza.metrics.Timer;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.operators.spec.OperatorSpec;
 import org.apache.samza.task.MessageCollector;
@@ -220,7 +220,7 @@ public WatermarkFunction getWatermarkFn() {
     }
 
     @Override
-    public SchedulingFunction getSchedulingFn() {
+    public ScheduledFunction getScheduledFn() {
       return null;
     }
   }
diff --git a/samza-core/src/test/java/org/apache/samza/operators/spec/OperatorSpecTestUtils.java b/samza-core/src/test/java/org/apache/samza/operators/spec/OperatorSpecTestUtils.java
index 9ca3f832af..b9a27677cd 100644
--- a/samza-core/src/test/java/org/apache/samza/operators/spec/OperatorSpecTestUtils.java
+++ b/samza-core/src/test/java/org/apache/samza/operators/spec/OperatorSpecTestUtils.java
@@ -28,7 +28,7 @@
 import java.util.Map;
 import org.apache.samza.operators.OperatorSpecGraph;
 import org.apache.samza.operators.TableImpl;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.serializers.SerializableSerde;
 import org.apache.samza.table.TableSpec;
@@ -72,7 +72,7 @@ private static void assertClonedOpSpec(OperatorSpec oOpSpec, OperatorSpec nOpSpe
     assertNotEquals(oOpSpec, nOpSpec);
     assertEquals(oOpSpec.getOpId(), nOpSpec.getOpId());
     assertEquals(oOpSpec.getOpCode(), nOpSpec.getOpCode());
-    assertSchedulingFnsNotEqual(oOpSpec.getSchedulingFn(), nOpSpec.getSchedulingFn());
+    assertScheduledFnsNotEqual(oOpSpec.getScheduledFn(), nOpSpec.getScheduledFn());
     assertWatermarkFnNotEqual(nOpSpec.getWatermarkFn(), nOpSpec.getWatermarkFn());
     assertAllOperators(oOpSpec.getRegisteredOperatorSpecs(), nOpSpec.getRegisteredOperatorSpecs());
   }
@@ -84,11 +84,11 @@ private static void assertWatermarkFnNotEqual(WatermarkFunction watermarkFn, Wat
     assertNotEquals(watermarkFn, watermarkFn1);
   }
 
-  private static void assertSchedulingFnsNotEqual(SchedulingFunction schedulingFn, SchedulingFunction schedulingFn1) {
-    if (schedulingFn == schedulingFn1 && schedulingFn == null) {
+  private static void assertScheduledFnsNotEqual(ScheduledFunction scheduledFn, ScheduledFunction scheduledFn1) {
+    if (scheduledFn == scheduledFn1 && scheduledFn == null) {
       return;
     }
-    assertNotEquals(schedulingFn, schedulingFn1);
+    assertNotEquals(scheduledFn, scheduledFn1);
   }
 
   private static void assertClonedTables(Map<TableSpec, TableImpl> originalTables, Map<TableSpec, TableImpl> clonedTables) {
diff --git a/samza-core/src/test/java/org/apache/samza/operators/spec/TestOperatorSpec.java b/samza-core/src/test/java/org/apache/samza/operators/spec/TestOperatorSpec.java
index be851b91b1..860e630314 100644
--- a/samza-core/src/test/java/org/apache/samza/operators/spec/TestOperatorSpec.java
+++ b/samza-core/src/test/java/org/apache/samza/operators/spec/TestOperatorSpec.java
@@ -24,7 +24,7 @@
 import java.util.List;
 import org.apache.samza.config.MapConfig;
 import org.apache.samza.operators.KV;
-import org.apache.samza.operators.KeyScheduler;
+import org.apache.samza.operators.Scheduler;
 import org.apache.samza.operators.data.TestMessageEnvelope;
 import org.apache.samza.operators.data.TestOutputMessageEnvelope;
 import org.apache.samza.operators.functions.FilterFunction;
@@ -33,7 +33,7 @@
 import org.apache.samza.operators.functions.MapFunction;
 import org.apache.samza.operators.functions.SinkFunction;
 import org.apache.samza.operators.functions.StreamTableJoinFunction;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.serializers.JsonSerdeV2;
 import org.apache.samza.serializers.KVSerde;
@@ -74,8 +74,8 @@ public TestOutputMessageEnvelope apply(TestMessageEnvelope m) {
     }
   }
 
-  private static class MapWithSchedulingFn implements MapFunction<TestMessageEnvelope, TestOutputMessageEnvelope>,
-                                                      SchedulingFunction<String, TestOutputMessageEnvelope> {
+  private static class MapWithScheduledFn implements MapFunction<TestMessageEnvelope, TestOutputMessageEnvelope>,
+                                                     ScheduledFunction<String, TestOutputMessageEnvelope> {
 
     @Override
     public TestOutputMessageEnvelope apply(TestMessageEnvelope m) {
@@ -83,12 +83,12 @@ public TestOutputMessageEnvelope apply(TestMessageEnvelope m) {
     }
 
     @Override
-    public void schedulingInit(KeyScheduler<String> keyScheduler) {
+    public void schedule(Scheduler<String> scheduler) {
 
     }
 
     @Override
-    public Collection<TestOutputMessageEnvelope> executeForKey(String key, long timestamp) {
+    public Collection<TestOutputMessageEnvelope> onCallback(String key, long timestamp) {
       return null;
     }
   }
@@ -165,8 +165,8 @@ public void testStreamOperatorSpecWithFlatMap() {
     assertTrue(cloneOperatorSpec.getTransformFn() instanceof FlatMapFunction);
     assertNull(streamOperatorSpec.getWatermarkFn());
     assertNull(cloneOperatorSpec.getWatermarkFn());
-    assertNull(streamOperatorSpec.getSchedulingFn());
-    assertNull(cloneOperatorSpec.getSchedulingFn());
+    assertNull(streamOperatorSpec.getScheduledFn());
+    assertNull(cloneOperatorSpec.getScheduledFn());
   }
 
   @Test
@@ -188,8 +188,8 @@ public void testStreamOperatorSpecWithMap() {
     assertNotEquals(userFn, clonedUserFn);
     assertNull(streamOperatorSpec.getWatermarkFn());
     assertNull(cloneOperatorSpec.getWatermarkFn());
-    assertNull(streamOperatorSpec.getSchedulingFn());
-    assertNull(cloneOperatorSpec.getSchedulingFn());
+    assertNull(streamOperatorSpec.getScheduledFn());
+    assertNull(cloneOperatorSpec.getScheduledFn());
   }
 
   @Test
@@ -210,8 +210,8 @@ public void testStreamOperatorSpecWithFilter() {
     assertNotEquals(userFn, clonedUserFn);
     assertNull(streamOperatorSpec.getWatermarkFn());
     assertNull(cloneOperatorSpec.getWatermarkFn());
-    assertNull(streamOperatorSpec.getSchedulingFn());
-    assertNull(cloneOperatorSpec.getSchedulingFn());
+    assertNull(streamOperatorSpec.getScheduledFn());
+    assertNull(cloneOperatorSpec.getScheduledFn());
   }
 
   @Test
@@ -361,13 +361,13 @@ public void testMapStreamOperatorSpecWithWatermark() {
     assertEquals(streamOperatorSpec.getWatermarkFn(), testMapFn);
     assertNotNull(cloneOperatorSpec.getWatermarkFn());
     assertNotEquals(cloneOperatorSpec.getTransformFn(), cloneOperatorSpec.getWatermarkFn());
-    assertNull(streamOperatorSpec.getSchedulingFn());
-    assertNull(cloneOperatorSpec.getSchedulingFn());
+    assertNull(streamOperatorSpec.getScheduledFn());
+    assertNull(cloneOperatorSpec.getScheduledFn());
   }
 
   @Test
-  public void testMapStreamOperatorSpecWithSchedulingFunction() {
-    MapWithSchedulingFn testMapFn = new MapWithSchedulingFn();
+  public void testMapStreamOperatorSpecWithScheduledFunction() {
+    MapWithScheduledFn testMapFn = new MapWithScheduledFn();
 
     StreamOperatorSpec<TestMessageEnvelope, TestOutputMessageEnvelope> streamOperatorSpec =
         OperatorSpecs.createMapOperatorSpec(testMapFn, "op0");
@@ -379,9 +379,9 @@ public void testMapStreamOperatorSpecWithSchedulingFunction() {
     assertNull(streamOperatorSpec.getWatermarkFn());
     assertNull(cloneOperatorSpec.getWatermarkFn());
     assertNotEquals(cloneOperatorSpec.getTransformFn(), cloneOperatorSpec.getWatermarkFn());
-    assertEquals(streamOperatorSpec.getSchedulingFn(), testMapFn);
-    assertNotNull(cloneOperatorSpec.getSchedulingFn());
-    assertNotEquals(streamOperatorSpec.getSchedulingFn(), cloneOperatorSpec.getSchedulingFn());
+    assertEquals(streamOperatorSpec.getScheduledFn(), testMapFn);
+    assertNotNull(cloneOperatorSpec.getScheduledFn());
+    assertNotEquals(streamOperatorSpec.getScheduledFn(), cloneOperatorSpec.getScheduledFn());
   }
 
   @Test
diff --git a/samza-core/src/test/java/org/apache/samza/operators/spec/TestPartitionByOperatorSpec.java b/samza-core/src/test/java/org/apache/samza/operators/spec/TestPartitionByOperatorSpec.java
index adeeb6df74..1d98580654 100644
--- a/samza-core/src/test/java/org/apache/samza/operators/spec/TestPartitionByOperatorSpec.java
+++ b/samza-core/src/test/java/org/apache/samza/operators/spec/TestPartitionByOperatorSpec.java
@@ -23,13 +23,13 @@
 import org.apache.samza.application.StreamApplicationDescriptorImpl;
 import org.apache.samza.config.Config;
 import org.apache.samza.config.JobConfig;
-import org.apache.samza.operators.KeyScheduler;
+import org.apache.samza.operators.Scheduler;
 import org.apache.samza.operators.MessageStream;
 import org.apache.samza.operators.OperatorSpecGraph;
 import org.apache.samza.operators.descriptors.GenericInputDescriptor;
 import org.apache.samza.operators.descriptors.GenericSystemDescriptor;
 import org.apache.samza.operators.functions.MapFunction;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.serializers.KVSerde;
 import org.apache.samza.serializers.NoOpSerde;
@@ -58,7 +58,7 @@ public class TestPartitionByOperatorSpec {
   private final String testJobId = "1";
   private final String testRepartitionedStreamName = "parByKey";
 
-  class SchedulingMapFn implements MapFunction<Object, String>, SchedulingFunction<String, Object> {
+  class ScheduledMapFn implements MapFunction<Object, String>, ScheduledFunction<String, Object> {
 
     @Override
     public String apply(Object message) {
@@ -66,12 +66,12 @@ public String apply(Object message) {
     }
 
     @Override
-    public void schedulingInit(KeyScheduler<String> keyScheduler) {
+    public void schedule(Scheduler<String> scheduler) {
 
     }
 
     @Override
-    public Collection<Object> executeForKey(String key, long timestamp) {
+    public Collection<Object> onCallback(String key, long timestamp) {
       return null;
     }
   }
@@ -117,7 +117,7 @@ public void testPartitionBy() {
     assertTrue(inputOpSpec.getKeySerde() instanceof NoOpSerde);
     assertTrue(inputOpSpec.getValueSerde() instanceof NoOpSerde);
     assertTrue(inputOpSpec.isKeyed());
-    assertNull(inputOpSpec.getSchedulingFn());
+    assertNull(inputOpSpec.getScheduledFn());
     assertNull(inputOpSpec.getWatermarkFn());
     InputOperatorSpec originInputSpec = inputOpSpecs.get(testinputDescriptor.getStreamId());
     assertTrue(originInputSpec.getRegisteredOperatorSpecs().toArray()[0] instanceof PartitionByOperatorSpec);
@@ -126,7 +126,7 @@ public void testPartitionBy() {
     assertEquals(reparOpSpec.getKeyFunction(), keyFn);
     assertEquals(reparOpSpec.getValueFunction(), valueFn);
     assertEquals(reparOpSpec.getOutputStream().getStreamId(), reparOpSpec.getOpId());
-    assertNull(reparOpSpec.getSchedulingFn());
+    assertNull(reparOpSpec.getScheduledFn());
     assertNull(reparOpSpec.getWatermarkFn());
   }
 
@@ -144,7 +144,7 @@ public void testPartitionByWithNoSerde() {
     assertNull(inputOpSpec.getKeySerde());
     assertNull(inputOpSpec.getValueSerde());
     assertTrue(inputOpSpec.isKeyed());
-    assertNull(inputOpSpec.getSchedulingFn());
+    assertNull(inputOpSpec.getScheduledFn());
     assertNull(inputOpSpec.getWatermarkFn());
     InputOperatorSpec originInputSpec = streamAppDesc.getInputOperators().get(testinputDescriptor.getStreamId());
     assertTrue(originInputSpec.getRegisteredOperatorSpecs().toArray()[0] instanceof PartitionByOperatorSpec);
@@ -153,7 +153,7 @@ public void testPartitionByWithNoSerde() {
     assertEquals(reparOpSpec.getKeyFunction(), keyFn);
     assertEquals(reparOpSpec.getValueFunction(), valueFn);
     assertEquals(reparOpSpec.getOutputStream().getStreamId(), reparOpSpec.getOpId());
-    assertNull(reparOpSpec.getSchedulingFn());
+    assertNull(reparOpSpec.getScheduledFn());
     assertNull(reparOpSpec.getWatermarkFn());
   }
 
@@ -169,8 +169,8 @@ public void testCopy() {
   }
 
   @Test(expected = IllegalArgumentException.class)
-  public void testSchedulingFunctionAsKeyFn() {
-    SchedulingMapFn keyFn = new SchedulingMapFn();
+  public void testScheduledFunctionAsKeyFn() {
+    ScheduledMapFn keyFn = new ScheduledMapFn();
     new StreamApplicationDescriptorImpl(appDesc -> {
         MessageStream<Object> inputStream = appDesc.getInputStream(testinputDescriptor);
         inputStream.partitionBy(keyFn, m -> m, "parByKey");
@@ -187,8 +187,8 @@ public void testWatermarkFunctionAsKeyFn() {
   }
 
   @Test(expected = IllegalArgumentException.class)
-  public void testSchedulingFunctionAsValueFn() {
-    SchedulingMapFn valueFn = new SchedulingMapFn();
+  public void testScheduledFunctionAsValueFn() {
+    ScheduledMapFn valueFn = new ScheduledMapFn();
     new StreamApplicationDescriptorImpl(appDesc -> {
         MessageStream<Object> inputStream = appDesc.getInputStream(testinputDescriptor);
         inputStream.partitionBy(m -> m.toString(), valueFn, "parByKey");
diff --git a/samza-core/src/test/java/org/apache/samza/operators/spec/TestWindowOperatorSpec.java b/samza-core/src/test/java/org/apache/samza/operators/spec/TestWindowOperatorSpec.java
index 32fb490157..41973b2294 100644
--- a/samza-core/src/test/java/org/apache/samza/operators/spec/TestWindowOperatorSpec.java
+++ b/samza-core/src/test/java/org/apache/samza/operators/spec/TestWindowOperatorSpec.java
@@ -19,8 +19,8 @@
 
 package org.apache.samza.operators.spec;
 
-import org.apache.samza.operators.KeyScheduler;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.Scheduler;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.serializers.Serde;
 import org.apache.samza.operators.functions.FoldLeftFunction;
@@ -90,8 +90,8 @@ public void testTriggerIntervalWithSingleTimeTrigger() {
   }
 
   @Test(expected = IllegalArgumentException.class)
-  public void testIllegalSchedulingFunctionAsInitializer() {
-    class TimedSupplierFunction implements SupplierFunction<Collection>, SchedulingFunction<Object, Collection> {
+  public void testIllegalScheduledFunctionAsInitializer() {
+    class TimedSupplierFunction implements SupplierFunction<Collection>, ScheduledFunction<Object, Collection> {
 
       @Override
       public Collection get() {
@@ -99,12 +99,12 @@ public Collection get() {
       }
 
       @Override
-      public void schedulingInit(KeyScheduler<Object> keyScheduler) {
+      public void schedule(Scheduler<Object> scheduler) {
 
       }
 
       @Override
-      public Collection<Collection> executeForKey(Object key, long timestamp) {
+      public Collection<Collection> onCallback(Object key, long timestamp) {
         return null;
       }
     }
@@ -138,8 +138,8 @@ public Long getOutputWatermark() {
   }
 
   @Test(expected = IllegalArgumentException.class)
-  public void testIllegalSchedulingFunctionAsKeyFn() {
-    class SchedulingMapFunction implements MapFunction<Object, Object>, SchedulingFunction<Object, Object> {
+  public void testIllegalScheduledFunctionAsKeyFn() {
+    class ScheduledMapFunction implements MapFunction<Object, Object>, ScheduledFunction<Object, Object> {
 
       @Override
       public Object apply(Object message) {
@@ -147,16 +147,16 @@ public Object apply(Object message) {
       }
 
       @Override
-      public void schedulingInit(KeyScheduler<Object> keyScheduler) {
+      public void schedule(Scheduler<Object> scheduler) {
 
       }
 
       @Override
-      public Collection<Object> executeForKey(Object key, long timestamp) {
+      public Collection<Object> onCallback(Object key, long timestamp) {
         return null;
       }
     }
-    keyFn = new SchedulingMapFunction();
+    keyFn = new ScheduledMapFunction();
 
     getWindowOperatorSpec("w0");
   }
@@ -186,8 +186,8 @@ public Long getOutputWatermark() {
   }
 
   @Test(expected = IllegalArgumentException.class)
-  public void testIllegalSchedulingFunctionAsEventTimeFn() {
-    class SchedulingMapFunction implements MapFunction<Object, Long>, SchedulingFunction<Object, Object> {
+  public void testIllegalScheduledFunctionAsEventTimeFn() {
+    class ScheduledMapFunction implements MapFunction<Object, Long>, ScheduledFunction<Object, Object> {
 
       @Override
       public Long apply(Object message) {
@@ -195,16 +195,16 @@ public Long apply(Object message) {
       }
 
       @Override
-      public void schedulingInit(KeyScheduler<Object> keyScheduler) {
+      public void schedule(Scheduler<Object> scheduler) {
 
       }
 
       @Override
-      public Collection<Object> executeForKey(Object key, long timestamp) {
+      public Collection<Object> onCallback(Object key, long timestamp) {
         return null;
       }
     }
-    timeFn = new SchedulingMapFunction();
+    timeFn = new ScheduledMapFunction();
 
     getWindowOperatorSpec("w0");
   }
@@ -234,9 +234,9 @@ public Long getOutputWatermark() {
   }
 
   @Test
-  public void testSchedulingFunctionAsFoldLeftFn() {
-    class SchedulingFoldLeftFunction
-        implements FoldLeftFunction<Object, Collection>, SchedulingFunction<Object, Collection> {
+  public void testScheduledFunctionAsFoldLeftFn() {
+    class ScheduledFoldLeftFunction
+        implements FoldLeftFunction<Object, Collection>, ScheduledFunction<Object, Collection> {
 
       @Override
       public Collection apply(Object message, Collection oldValue) {
@@ -245,19 +245,19 @@ public Collection apply(Object message, Collection oldValue) {
       }
 
       @Override
-      public void schedulingInit(KeyScheduler<Object> keyScheduler) {
+      public void schedule(Scheduler<Object> scheduler) {
 
       }
 
       @Override
-      public Collection<Collection> executeForKey(Object key, long timestamp) {
+      public Collection<Collection> onCallback(Object key, long timestamp) {
         return null;
       }
     }
 
-    foldFn = new SchedulingFoldLeftFunction();
+    foldFn = new ScheduledFoldLeftFunction();
     WindowOperatorSpec<Object, Object, Collection> windowSpec = getWindowOperatorSpec("w0");
-    assertEquals(windowSpec.getSchedulingFn(), foldFn);
+    assertEquals(windowSpec.getScheduledFn(), foldFn);
     assertNull(windowSpec.getWatermarkFn());
   }
 
@@ -285,7 +285,7 @@ public Collection apply(Object message, Collection oldValue) {
     foldFn = new WatermarkFoldLeftFunction();
     WindowOperatorSpec<Object, Object, Collection> windowSpec = getWindowOperatorSpec("w0");
     assertEquals(windowSpec.getWatermarkFn(), foldFn);
-    assertNull(windowSpec.getSchedulingFn());
+    assertNull(windowSpec.getScheduledFn());
   }
 
   @Test
diff --git a/samza-core/src/test/java/org/apache/samza/task/TestSystemTimerScheduler.java b/samza-core/src/test/java/org/apache/samza/task/TestSystemTimerScheduler.java
index 038ff27680..7e6324d62a 100644
--- a/samza-core/src/test/java/org/apache/samza/task/TestSystemTimerScheduler.java
+++ b/samza-core/src/test/java/org/apache/samza/task/TestSystemTimerScheduler.java
@@ -51,7 +51,7 @@ private ScheduledExecutorService createExecutorService() {
 
   private void fireTimers(SystemTimerScheduler factory) {
     factory.removeReadyTimers().entrySet().forEach(entry -> {
-        entry.getValue().execute(entry.getKey().getKey(), mock(MessageCollector.class), mock(TaskCoordinator.class));
+        entry.getValue().onCallback(entry.getKey().getKey(), mock(MessageCollector.class), mock(TaskCoordinator.class));
       });
   }
 
diff --git a/samza-sql/src/test/java/org/apache/samza/sql/translator/TestProjectTranslator.java b/samza-sql/src/test/java/org/apache/samza/sql/translator/TestProjectTranslator.java
index 8b17f59a9c..3046c1fa49 100644
--- a/samza-sql/src/test/java/org/apache/samza/sql/translator/TestProjectTranslator.java
+++ b/samza-sql/src/test/java/org/apache/samza/sql/translator/TestProjectTranslator.java
@@ -39,7 +39,7 @@
 import org.apache.samza.operators.MessageStream;
 import org.apache.samza.operators.MessageStreamImpl;
 import org.apache.samza.operators.functions.MapFunction;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.operators.functions.WatermarkFunction;
 import org.apache.samza.operators.spec.OperatorSpec;
 import org.apache.samza.operators.spec.StreamOperatorSpec;
@@ -192,7 +192,7 @@ public WatermarkFunction getWatermarkFn() {
       }
 
       @Override
-      public SchedulingFunction getSchedulingFn() {
+      public ScheduledFunction getScheduledFn() {
         return null;
       }
     };
diff --git a/samza-test/src/test/java/org/apache/samza/test/framework/TestSchedulingApp.java b/samza-test/src/test/java/org/apache/samza/test/framework/TestSchedulingApp.java
index 8a4f2764ff..db78e8cb21 100644
--- a/samza-test/src/test/java/org/apache/samza/test/framework/TestSchedulingApp.java
+++ b/samza-test/src/test/java/org/apache/samza/test/framework/TestSchedulingApp.java
@@ -26,10 +26,10 @@
 import java.util.List;
 import org.apache.samza.application.StreamApplication;
 import org.apache.samza.application.StreamApplicationDescriptor;
-import org.apache.samza.operators.KeyScheduler;
+import org.apache.samza.operators.Scheduler;
 import org.apache.samza.operators.MessageStream;
 import org.apache.samza.operators.functions.FlatMapFunction;
-import org.apache.samza.operators.functions.SchedulingFunction;
+import org.apache.samza.operators.functions.ScheduledFunction;
 import org.apache.samza.serializers.JsonSerdeV2;
 import org.apache.samza.system.kafka.KafkaInputDescriptor;
 import org.apache.samza.system.kafka.KafkaSystemDescriptor;
@@ -44,7 +44,7 @@ public void describe(StreamApplicationDescriptor appDesc) {
     KafkaSystemDescriptor ksd = new KafkaSystemDescriptor("kafka");
     KafkaInputDescriptor<PageView> isd = ksd.getInputDescriptor(PAGE_VIEWS, serde);
     final MessageStream<PageView> pageViews = appDesc.getInputStream(isd);
-    final MessageStream<PageView> output = pageViews.flatMap(new FlatmapSchedulingFn());
+    final MessageStream<PageView> output = pageViews.flatMap(new FlatmapScheduledFn());
 
     MessageStreamAssert.that("Output from scheduling function should container all complete messages", output, serde)
         .containsInAnyOrder(
@@ -56,15 +56,15 @@ public void describe(StreamApplicationDescriptor appDesc) {
             ));
   }
 
-  private static class FlatmapSchedulingFn
-      implements FlatMapFunction<PageView, PageView>, SchedulingFunction<String, PageView> {
+  private static class FlatmapScheduledFn
+      implements FlatMapFunction<PageView, PageView>, ScheduledFunction<String, PageView> {
 
     private transient List<PageView> pageViews;
-    private transient KeyScheduler<String> keyScheduler;
+    private transient Scheduler<String> scheduler;
 
     @Override
-    public void schedulingInit(KeyScheduler<String> keyScheduler) {
-      this.keyScheduler = keyScheduler;
+    public void schedule(Scheduler<String> scheduler) {
+      this.scheduler = scheduler;
       this.pageViews = new ArrayList<>();
     }
 
@@ -76,13 +76,13 @@ public Collection<PageView> apply(PageView message) {
       if (pageViews.size() == 2) {
         //got all messages for this task
         final long time = System.currentTimeMillis() + 100;
-        keyScheduler.schedule("CompleteScheduler", time);
+        scheduler.schedule("CompleteScheduler", time);
       }
       return Collections.emptyList();
     }
 
     @Override
-    public Collection<PageView> executeForKey(String key, long time) {
+    public Collection<PageView> onCallback(String key, long time) {
       return pageViews;
     }
   }

From e7abf9f467f8e03815228314c89dbee1c731379b Mon Sep 17 00:00:00 2001
From: Cameron Lee <calee@linkedin.com>
Date: Thu, 20 Sep 2018 14:49:42 -0700
Subject: [PATCH 4/4] doc updates, SystemTimerScheduler renamed to
 EpochTimeScheduler

---
 .../org/apache/samza/operators/Scheduler.java | 14 ++++++-------
 .../functions/ScheduledFunction.java          | 21 ++++++++++++-------
 .../org/apache/samza/task/TaskContext.java    |  4 ++--
 .../samza/container/TaskContextImpl.java      |  8 +++----
 .../org/apache/samza/task/AsyncRunLoop.java   |  6 +++---
 ...Scheduler.java => EpochTimeScheduler.java} |  8 +++----
 ...duler.java => TestEpochTimeScheduler.java} | 16 +++++++-------
 7 files changed, 40 insertions(+), 37 deletions(-)
 rename samza-core/src/main/java/org/apache/samza/task/{SystemTimerScheduler.java => EpochTimeScheduler.java} (95%)
 rename samza-core/src/test/java/org/apache/samza/task/{TestSystemTimerScheduler.java => TestEpochTimeScheduler.java} (89%)

diff --git a/samza-api/src/main/java/org/apache/samza/operators/Scheduler.java b/samza-api/src/main/java/org/apache/samza/operators/Scheduler.java
index 05bea38bca..77148f0a92 100644
--- a/samza-api/src/main/java/org/apache/samza/operators/Scheduler.java
+++ b/samza-api/src/main/java/org/apache/samza/operators/Scheduler.java
@@ -20,21 +20,19 @@
 package org.apache.samza.operators;
 
 /**
- * Manages scheduling keys to be triggered later. See {@link org.apache.samza.operators.functions.ScheduledFunction}
- * for details.
- * @param <K> type of the key
+ * Allows scheduling {@link org.apache.samza.operators.functions.ScheduledFunction} callbacks to be invoked later.
+ * @param <K> type of the key to schedule
  */
 public interface Scheduler<K> {
-
   /**
-   * Schedule a key to be triggered at {@code timestamp}.
-   * @param key unique key
-   * @param timestamp epoch time when the key will be triggered, in milliseconds
+   * Schedule a callback for the {@code key} to be invoked at {@code timestamp}.
+   * @param key unique key associated with the callback to schedule
+   * @param timestamp epoch time when the callback for the key will be invoked, in milliseconds
    */
   void schedule(K key, long timestamp);
 
   /**
-   * Delete the scheduler entry for the provided key.
+   * Delete the scheduled callback for the provided {@code key}.
    * @param key key to delete
    */
   void delete(K key);
diff --git a/samza-api/src/main/java/org/apache/samza/operators/functions/ScheduledFunction.java b/samza-api/src/main/java/org/apache/samza/operators/functions/ScheduledFunction.java
index b75b335a07..952948c515 100644
--- a/samza-api/src/main/java/org/apache/samza/operators/functions/ScheduledFunction.java
+++ b/samza-api/src/main/java/org/apache/samza/operators/functions/ScheduledFunction.java
@@ -25,7 +25,7 @@
 
 
 /**
- * Allows scheduling with key(s) and is invoked when the specified time(s) occurs.
+ * Allows scheduling a callback for a specific epoch-time.
  * Key must be a unique identifier for its corresponding logic to execute, and is provided in the callback when the
  * corresponding schedule time occurs.
  *
@@ -33,16 +33,23 @@
  * Example of a {@link FlatMapFunction} with {@link ScheduledFunction}:
  * <pre>{@code
  *    public class ExampleScheduledFn implements FlatMapFunction<String, String>, ScheduledFunction<String, String> {
+ *      // for recurring callbacks, keep track of the scheduler from "schedule"
+ *      private Scheduler scheduler;
+ *
  *      public void schedule(Scheduler scheduler) {
+ *        // save the scheduler for recurring callbacks
+ *        this.scheduler = scheduler;
  *        long time = System.currentTimeMillis() + 5000; // fire after 5 sec
- *        scheduler.schedule("example-scheduler-logic", time);
+ *        scheduler.schedule("do-delayed-logic", time);
  *      }
  *      public Collection<String> apply(String s) {
  *        ...
  *      }
  *      public Collection<String> onCallback(String key, long timestamp) {
- *        // fired with key as "example-scheduler-logic"
+ *        // do some logic for key "do-delayed-logic"
  *        ...
+ *        // for recurring callbacks, call the saved scheduler again
+ *        this.scheduler.schedule("example-process", System.currentTimeMillis() + 5000);
  *      }
  *    }
  * }</pre>
@@ -50,18 +57,16 @@
  * @param <OM> type of the output
  */
 public interface ScheduledFunction<K, OM> {
-
   /**
-   * Initialize the function for scheduling, such as setting some initial scheduling logic or saving the
-   * {@code scheduler} for later use.
+   * Allows scheduling the initial callback(s) and saving the {@code scheduler} for later use for recurring callbacks.
    * @param scheduler used to specify the schedule time(s) and key(s)
    */
   void schedule(Scheduler<K> scheduler);
 
   /**
    * Returns the output from the scheduling logic corresponding to the key that was triggered.
-   * @param key key corresponding to the scheduling logic that got triggered
-   * @param timestamp schedule time that was set for the key, in milliseconds since epoch
+   * @param key key corresponding to the callback that got invoked
+   * @param timestamp schedule time that was set for the callback for the key, in milliseconds since epoch
    * @return {@link Collection} of output elements
    */
   Collection<OM> onCallback(K key, long timestamp);
diff --git a/samza-api/src/main/java/org/apache/samza/task/TaskContext.java b/samza-api/src/main/java/org/apache/samza/task/TaskContext.java
index f142d5ca8f..eccedba3f2 100644
--- a/samza-api/src/main/java/org/apache/samza/task/TaskContext.java
+++ b/samza-api/src/main/java/org/apache/samza/task/TaskContext.java
@@ -77,7 +77,7 @@ default Object getUserContext() {
   }
 
   /**
-   * Register a keyed callback in this task.
+   * Schedule the {@code callback} for the provided {@code key} to be invoked at epoch-time {@code timestamp}.
    * The callback will be invoked exclusively with any other operations for this task,
    * e.g. processing, windowing and commit.
    * @param key key for the callback
@@ -88,7 +88,7 @@ default Object getUserContext() {
   <K> void scheduleCallback(K key, long timestamp, ScheduledCallback<K> callback);
 
   /**
-   * Delete the keyed callback in this task.
+   * Delete the scheduled {@code callback} for the {@code key}.
    * Deletion only happens if the callback hasn't been fired. Otherwise it will not interrupt.
    * @param key callback key
    * @param <K> type of the key
diff --git a/samza-core/src/main/java/org/apache/samza/container/TaskContextImpl.java b/samza-core/src/main/java/org/apache/samza/container/TaskContextImpl.java
index f1d265a72a..bea6373baf 100644
--- a/samza-core/src/main/java/org/apache/samza/container/TaskContextImpl.java
+++ b/samza-core/src/main/java/org/apache/samza/container/TaskContextImpl.java
@@ -29,7 +29,7 @@
 import org.apache.samza.system.SystemStreamPartition;
 import org.apache.samza.table.Table;
 import org.apache.samza.table.TableManager;
-import org.apache.samza.task.SystemTimerScheduler;
+import org.apache.samza.task.EpochTimeScheduler;
 import org.apache.samza.task.TaskContext;
 import org.apache.samza.scheduler.ScheduledCallback;
 import org.slf4j.Logger;
@@ -53,7 +53,7 @@ public class TaskContextImpl implements TaskContext {
   private final JobModel jobModel;
   private final StreamMetadataCache streamMetadataCache;
   private final Map<String, Object> objectRegistry = new HashMap<>();
-  private final SystemTimerScheduler timerScheduler;
+  private final EpochTimeScheduler timerScheduler;
 
   private Object userContext = null;
 
@@ -76,7 +76,7 @@ public TaskContextImpl(TaskName taskName,
     this.tableManager = tableManager;
     this.jobModel = jobModel;
     this.streamMetadataCache = streamMetadataCache;
-    this.timerScheduler = SystemTimerScheduler.create(timerExecutor);
+    this.timerScheduler = EpochTimeScheduler.create(timerExecutor);
   }
 
   @Override
@@ -159,7 +159,7 @@ public StreamMetadataCache getStreamMetadataCache() {
     return streamMetadataCache;
   }
 
-  public SystemTimerScheduler getTimerScheduler() {
+  public EpochTimeScheduler getTimerScheduler() {
     return timerScheduler;
   }
 }
diff --git a/samza-core/src/main/java/org/apache/samza/task/AsyncRunLoop.java b/samza-core/src/main/java/org/apache/samza/task/AsyncRunLoop.java
index dc98d204e5..111869c2ec 100644
--- a/samza-core/src/main/java/org/apache/samza/task/AsyncRunLoop.java
+++ b/samza-core/src/main/java/org/apache/samza/task/AsyncRunLoop.java
@@ -374,9 +374,9 @@ public void run() {
         }, commitMs, commitMs, TimeUnit.MILLISECONDS);
       }
 
-      final SystemTimerScheduler timerScheduler = task.context().getTimerScheduler();
-      if (timerScheduler != null) {
-        timerScheduler.registerListener(() -> {
+      final EpochTimeScheduler epochTimeScheduler = task.context().getTimerScheduler();
+      if (epochTimeScheduler != null) {
+        epochTimeScheduler.registerListener(() -> {
             state.needScheduler();
           });
       }
diff --git a/samza-core/src/main/java/org/apache/samza/task/SystemTimerScheduler.java b/samza-core/src/main/java/org/apache/samza/task/EpochTimeScheduler.java
similarity index 95%
rename from samza-core/src/main/java/org/apache/samza/task/SystemTimerScheduler.java
rename to samza-core/src/main/java/org/apache/samza/task/EpochTimeScheduler.java
index f89175e190..3f50d9a477 100644
--- a/samza-core/src/main/java/org/apache/samza/task/SystemTimerScheduler.java
+++ b/samza-core/src/main/java/org/apache/samza/task/EpochTimeScheduler.java
@@ -36,7 +36,7 @@
  * 2) keeps track of the timers created and timers that are ready.
  * 3) triggers listener whenever a timer fires.
  */
-public class SystemTimerScheduler {
+public class EpochTimeScheduler {
 
   /**
    * For run loop to listen to timer firing so it can schedule the callbacks.
@@ -50,11 +50,11 @@ public interface TimerListener {
   private final Map<TimerKey<?>, ScheduledCallback> readyTimers = new ConcurrentHashMap<>();
   private TimerListener timerListener;
 
-  public static SystemTimerScheduler create(ScheduledExecutorService executor) {
-    return new SystemTimerScheduler(executor);
+  public static EpochTimeScheduler create(ScheduledExecutorService executor) {
+    return new EpochTimeScheduler(executor);
   }
 
-  private SystemTimerScheduler(ScheduledExecutorService executor) {
+  private EpochTimeScheduler(ScheduledExecutorService executor) {
     this.executor = executor;
   }
 
diff --git a/samza-core/src/test/java/org/apache/samza/task/TestSystemTimerScheduler.java b/samza-core/src/test/java/org/apache/samza/task/TestEpochTimeScheduler.java
similarity index 89%
rename from samza-core/src/test/java/org/apache/samza/task/TestSystemTimerScheduler.java
rename to samza-core/src/test/java/org/apache/samza/task/TestEpochTimeScheduler.java
index 7e6324d62a..e0da2e95b9 100644
--- a/samza-core/src/test/java/org/apache/samza/task/TestSystemTimerScheduler.java
+++ b/samza-core/src/test/java/org/apache/samza/task/TestEpochTimeScheduler.java
@@ -36,7 +36,7 @@
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
-public class TestSystemTimerScheduler {
+public class TestEpochTimeScheduler {
 
   private ScheduledExecutorService createExecutorService() {
     ScheduledExecutorService service = mock(ScheduledExecutorService.class);
@@ -49,7 +49,7 @@ private ScheduledExecutorService createExecutorService() {
     return service;
   }
 
-  private void fireTimers(SystemTimerScheduler factory) {
+  private void fireTimers(EpochTimeScheduler factory) {
     factory.removeReadyTimers().entrySet().forEach(entry -> {
         entry.getValue().onCallback(entry.getKey().getKey(), mock(MessageCollector.class), mock(TaskCoordinator.class));
       });
@@ -57,7 +57,7 @@ private void fireTimers(SystemTimerScheduler factory) {
 
   @Test
   public void testSingleTimer() {
-    SystemTimerScheduler scheduler = SystemTimerScheduler.create(createExecutorService());
+    EpochTimeScheduler scheduler = EpochTimeScheduler.create(createExecutorService());
     List<String> results = new ArrayList<>();
     scheduler.setTimer("single-timer", 1, (key, collector, coordinator) -> {
         results.add(key);
@@ -71,7 +71,7 @@ public void testSingleTimer() {
 
   @Test
   public void testMultipleTimers() {
-    SystemTimerScheduler scheduler = SystemTimerScheduler.create(createExecutorService());
+    EpochTimeScheduler scheduler = EpochTimeScheduler.create(createExecutorService());
     List<String> results = new ArrayList<>();
     scheduler.setTimer("multiple-timer-3", 3, (key, collector, coordinator) -> {
         results.add(key + ":3");
@@ -97,7 +97,7 @@ public void testMultipleKeys() {
     Object key2 = new Object();
     List<String> results = new ArrayList<>();
 
-    SystemTimerScheduler scheduler = SystemTimerScheduler.create(createExecutorService());
+    EpochTimeScheduler scheduler = EpochTimeScheduler.create(createExecutorService());
     scheduler.setTimer(key1, 2, (key, collector, coordinator) -> {
         assertEquals(key, key1);
         results.add("key1:2");
@@ -120,7 +120,7 @@ public void testMultipleKeyTypes() {
     Long key2 = Long.MAX_VALUE;
     List<String> results = new ArrayList<>();
 
-    SystemTimerScheduler scheduler = SystemTimerScheduler.create(createExecutorService());
+    EpochTimeScheduler scheduler = EpochTimeScheduler.create(createExecutorService());
     scheduler.setTimer(key1, 1, (key, collector, coordinator) -> {
         assertEquals(key, key1);
         results.add("key:1");
@@ -144,7 +144,7 @@ public void testRemoveTimer() {
     when(future.cancel(anyBoolean())).thenReturn(true);
     when(service.schedule((Runnable) anyObject(), anyLong(), anyObject())).thenAnswer(invocation -> future);
 
-    SystemTimerScheduler scheduler = SystemTimerScheduler.create(service);
+    EpochTimeScheduler scheduler = EpochTimeScheduler.create(service);
     List<String> results = new ArrayList<>();
     scheduler.setTimer("timer", 1, (key, collector, coordinator) -> {
         results.add(key);
@@ -160,7 +160,7 @@ public void testRemoveTimer() {
 
   @Test
   public void testTimerListener() {
-    SystemTimerScheduler scheduler = SystemTimerScheduler.create(createExecutorService());
+    EpochTimeScheduler scheduler = EpochTimeScheduler.create(createExecutorService());
     List<String> results = new ArrayList<>();
     scheduler.registerListener(() -> {
         results.add("timer-listener");