From e975ee8e1683554afaf4363d20ae659780d8aedd Mon Sep 17 00:00:00 2001
From: Zhenxiao Luo <zluo@twitter.com>
Date: Sat, 1 Feb 2020 22:14:38 -0800
Subject: [PATCH] Not use ConcurrentHashMap in CoordinatorRuleManager.rules

---
 .../server/router/CoordinatorRuleManager.java | 21 +++++++------------
 1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/server/src/main/java/org/apache/druid/server/router/CoordinatorRuleManager.java b/server/src/main/java/org/apache/druid/server/router/CoordinatorRuleManager.java
index 473b5c9ca9a1..d18a6d65afab 100644
--- a/server/src/main/java/org/apache/druid/server/router/CoordinatorRuleManager.java
+++ b/server/src/main/java/org/apache/druid/server/router/CoordinatorRuleManager.java
@@ -41,10 +41,9 @@
 import org.joda.time.Duration;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.atomic.AtomicReference;
 
@@ -58,7 +57,7 @@ public class CoordinatorRuleManager
   private final ObjectMapper jsonMapper;
   private final Supplier<TieredBrokerConfig> config;
 
-  private final AtomicReference<ConcurrentHashMap<String, List<Rule>>> rules;
+  private final AtomicReference<Map<String, List<Rule>>> rules;
 
   private final DruidLeaderClient druidLeaderClient;
 
@@ -80,7 +79,7 @@ public CoordinatorRuleManager(
     this.druidLeaderClient = druidLeaderClient;
 
     this.rules = new AtomicReference<>(
-        new ConcurrentHashMap<String, List<Rule>>()
+        Collections.emptyMap()
     );
   }
 
@@ -120,7 +119,7 @@ public void stop()
         return;
       }
 
-      rules.set(new ConcurrentHashMap<String, List<Rule>>());
+      rules.set(Collections.emptyMap());
 
       started = false;
       exec.shutdownNow();
@@ -149,17 +148,13 @@ public void poll()
         );
       }
 
-      ConcurrentHashMap<String, List<Rule>> newRules = new ConcurrentHashMap<>(
-          (Map<String, List<Rule>>) jsonMapper.readValue(
+      rules.set(
+          Collections.unmodifiableMap(jsonMapper.readValue(
               response.getContent(), new TypeReference<Map<String, List<Rule>>>()
               {
               }
-          )
+          ))
       );
-
-      log.debug("Got [%,d] rules", newRules.size());
-
-      rules.set(newRules);
     }
     catch (Exception e) {
       log.error(e, "Exception while polling for rules");
@@ -169,7 +164,7 @@ public void poll()
   public List<Rule> getRulesWithDefault(final String dataSource)
   {
     List<Rule> rulesWithDefault = new ArrayList<>();
-    ConcurrentMap<String, List<Rule>> theRules = rules.get();
+    Map<String, List<Rule>> theRules = rules.get();
     List<Rule> dataSourceRules = theRules.get(dataSource);
     if (dataSourceRules != null) {
       rulesWithDefault.addAll(dataSourceRules);