From 092339ffca167518208287151616e44e27697c50 Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Sun, 24 Oct 2021 23:57:26 -0700
Subject: [PATCH 01/14] meter changes - intial commit

---
 .../metrics_new/async_instruments.h           |  88 ++++++
 api/include/opentelemetry/metrics_new/meter.h | 276 ++++++++++++++++++
 .../metrics_new/meter_provider.h              |  33 +++
 .../metrics_new/observer_result.h             |  41 +++
 .../opentelemetry/metrics_new/provider.h      |  59 ++++
 .../metrics_new/sync_instruments.h            |  87 ++++++
 6 files changed, 584 insertions(+)
 create mode 100644 api/include/opentelemetry/metrics_new/async_instruments.h
 create mode 100644 api/include/opentelemetry/metrics_new/meter.h
 create mode 100644 api/include/opentelemetry/metrics_new/meter_provider.h
 create mode 100644 api/include/opentelemetry/metrics_new/observer_result.h
 create mode 100644 api/include/opentelemetry/metrics_new/provider.h
 create mode 100644 api/include/opentelemetry/metrics_new/sync_instruments.h

diff --git a/api/include/opentelemetry/metrics_new/async_instruments.h b/api/include/opentelemetry/metrics_new/async_instruments.h
new file mode 100644
index 0000000000..867382ec19
--- /dev/null
+++ b/api/include/opentelemetry/metrics_new/async_instruments.h
@@ -0,0 +1,88 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#pragma once
+#ifdef ENABLE_METRICS_PREVIEW
+
+#  include "instrument.h"
+#  include "observer_result.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace metrics
+{
+
+template <class T>
+class ValueObserver : virtual public AsynchronousInstrument<T>
+{
+
+public:
+  ValueObserver() = default;
+
+  ValueObserver(nostd::string_view name,
+                nostd::string_view description,
+                nostd::string_view unit,
+                bool enabled,
+                void (*callback)(ObserverResult<T>))
+  {}
+
+  /*
+   * Updates the instruments aggregator with the new value. The labels should
+   * contain the keys and values to be associated with this value.
+   *
+   * @param value is the numerical representation of the metric being captured
+   * @param labels the set of labels, as key-value pairs
+   */
+  virtual void observe(T value, const common::KeyValueIterable &labels) override = 0;
+
+  /**
+   * Captures data by activating the callback function associated with the
+   * instrument and storing its return value.  Callbacks for asynchronous
+   * instruments are defined during construction.
+   *
+   * @param none
+   * @return none
+   */
+  virtual void run() override = 0;
+};
+
+template <class T>
+class SumObserver : virtual public AsynchronousInstrument<T>
+{
+
+public:
+  SumObserver() = default;
+
+  SumObserver(nostd::string_view name,
+              nostd::string_view description,
+              nostd::string_view unit,
+              bool enabled,
+              void (*callback)(ObserverResult<T>))
+  {}
+
+  virtual void observe(T value, const common::KeyValueIterable &labels) override = 0;
+
+  virtual void run() override = 0;
+};
+
+template <class T>
+class UpDownSumObserver : virtual public AsynchronousInstrument<T>
+{
+
+public:
+  UpDownSumObserver() = default;
+
+  UpDownSumObserver(nostd::string_view name,
+                    nostd::string_view description,
+                    nostd::string_view unit,
+                    bool enabled,
+                    void (*callback)(ObserverResult<T>))
+  {}
+
+  virtual void observe(T value, const common::KeyValueIterable &labels) override = 0;
+
+  virtual void run() override = 0;
+};
+
+}  // namespace metrics
+OPENTELEMETRY_END_NAMESPACE
+#endif
diff --git a/api/include/opentelemetry/metrics_new/meter.h b/api/include/opentelemetry/metrics_new/meter.h
new file mode 100644
index 0000000000..9712275de5
--- /dev/null
+++ b/api/include/opentelemetry/metrics_new/meter.h
@@ -0,0 +1,276 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#pragma once
+#ifdef ENABLE_METRICS_PREVIEW
+
+#  include "opentelemetry/metrics_new/async_instruments.h"
+#  include "opentelemetry/metrics_new/instrument.h"
+#  include "opentelemetry/metrics_new/sync_instruments.h"
+#  include "opentelemetry/nostd/shared_ptr.h"
+#  include "opentelemetry/nostd/span.h"
+#  include "opentelemetry/nostd/string_view.h"
+#  include "opentelemetry/version.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace metrics_new
+{
+/**
+ * Handles instrument creation and provides a facility for batch recording.
+ *
+ * This class provides methods to create new metric instruments, record a
+ * batch of values to a specified set of instruments, and collect
+ * measurements from all instruments.
+ *
+ */
+class Meter
+{
+public:
+  virtual ~Meter() = default;
+
+  /**
+   * Creates a Counter with the passed characteristics and returns a shared_ptr to that Counter.
+   *
+   * @param name the name of the new Counter.
+   * @param description a brief description of what the Counter is used for.
+   * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
+   * @param enabled a boolean value that turns on or off the metric instrument.
+   * @return a shared pointer to the created Counter.
+   * @throws NullPointerException if {@code name} is null
+   * @throws IllegalArgumentException if a different metric by the same name exists in this meter.
+   * @throws IllegalArgumentException if the {@code name} does not match spec requirements.
+   */
+  virtual nostd::shared_ptr<Counter<short>> CreateShortCounter(nostd::string_view name,
+                                                            nostd::string_view description = "",
+                                                            nostd::string_view unit = "",
+                                                            const bool enabled = true) = 0;
+
+  virtual nostd::shared_ptr<Counter<int>> CreateIntCounter(nostd::string_view name,
+                                                        nostd::string_view description = "",
+                                                        nostd::string_view unit = "",
+                                                        const bool enabled = true) = 0;
+
+  virtual nostd::shared_ptr<Counter<float>> CreateFloatCounter(nostd::string_view name,
+                                                            nostd::string_view description = "",
+                                                            nostd::string_view unit = "",
+                                                            const bool enabled = true) = 0;
+
+  virtual nostd::shared_ptr<Counter<double>> CreateDoubleCounter(nostd::string_view name,
+                                                              nostd::string_view description = "",
+                                                              nostd::string_view unit = "",
+                                                              const bool enabled = true) = 0;
+
+/**
+   * Creates a Asynchronouse (Observable) counter with the passed characteristics and returns a shared_ptr to that
+   * Observable Counter
+   *
+   * @param name the name of the new Observable Counter.
+   * @param description a brief description of what the Observable Counter is used for.
+   * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
+   * @param enabled a boolean value that turns on or off the metric instrument.
+   * @param callback the function to be observed by the instrument.
+   * @return a shared pointer to the created Observable Counter.
+   */
+  virtual nostd::shared_ptr<ObservableCounter<short>> CreateShortObservableCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<short>),
+      nostd::string_view description = "",
+      nostd::string_view unit = "",
+      const bool enabled = true
+      ) = 0;
+
+  virtual nostd::shared_ptr<ObservableCounter<int>> CreateIntObservableCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<int>),
+      nostd::string_view description = "",
+      nostd::string_view unit = "",
+      const bool enabled = true,
+      ) = 0;
+
+  virtual nostd::shared_ptr<ObservableCounter<float>> CreateFloatObservableCounter(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit = "",
+      const bool enabled = true,
+      void (*callback)(ObserverResult<float>)) = 0;
+
+  virtual nostd::shared_ptr<ObservableCounter<double>> CreateDoubleObservableCounter(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit = "",
+      const bool enabled = true,
+      void (*callback)(ObserverResult<double>)) = 0;
+
+  /**
+   * Creates a Histogram with the passed characteristics and returns a shared_ptr to that Histogram.
+   *
+   * @param name the name of the new Histogram.
+   * @param description a brief description of what the Histogram is used for.
+   * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
+   * @param enabled a boolean value that turns on or off the metric instrument.
+   * @return a shared pointer to the created Histogram.
+   */
+  virtual nostd::shared_ptr<Histogram<short>> CreateShortHistogram(nostd::string_view name,
+                                                            nostd::string_view description = "",
+                                                            nostd::string_view unit = "",
+                                                            const bool enabled = true) = 0;
+
+  virtual nostd::shared_ptr<Histogram<int>> CreateIntHistogram(nostd::string_view name,
+                                                        nostd::string_view description = "",
+                                                        nostd::string_view unit = "",
+                                                        const bool enabled = true) = 0;
+
+  virtual nostd::shared_ptr<Histogram<float>> CreateFloatHistogram(nostd::string_view name,
+                                                            nostd::string_view description = "",
+                                                            nostd::string_view unit = "",
+                                                            const bool enabled = true) = 0;
+
+  virtual nostd::shared_ptr<Histogram<double>> CreateDoubleHistogram(nostd::string_view name,
+                                                              nostd::string_view description = "",
+                                                              nostd::string_view unit = "",
+                                                              const bool enabled = true) = 0;
+
+
+/**
+   * Creates a Asynchronouse (Observable) Gauge with the passed characteristics and returns a shared_ptr to that
+   * Observable Counter
+   *
+   * @param name the name of the new Observable Gauge.
+   * @param description a brief description of what the Observable Gauge is used for.
+   * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
+   * @param enabled a boolean value that turns on or off the metric instrument.
+   * @param callback the function to be observed by the instrument.
+   * @return a shared pointer to the created Observable Gauge.
+   */
+  virtual nostd::shared_ptr<ObservableGauge<short>> CreateShortObservableGauge(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<short>),
+      nostd::string_view description = "",
+      nostd::string_view unit = "",
+      const bool enabled = true
+      ) = 0;
+
+  virtual nostd::shared_ptr<ObservableGauge<int>> CreateIntObservableGauge(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<int>),
+      nostd::string_view description = "",
+      nostd::string_view unit = "",
+      const bool enabled = true,
+      ) = 0;
+
+  virtual nostd::shared_ptr<ObservableGauge<float>> CreateFloatObservableGauge(
+      nostd::string_view name,
+      nostd::string_view description,
+      nostd::string_view unit,
+      const bool enabled,
+      void (*callback)(ObserverResult<float>)) = 0;
+
+  virtual nostd::shared_ptr<ObservableGauge<double>> CreateDoubleObservableGauge(
+      nostd::string_view name,
+      nostd::string_view description,
+      nostd::string_view unit,
+      const bool enabled,
+      void (*callback)(ObserverResult<double>)) = 0;
+
+  /**
+   * Creates an UpDownCounter with the passed characteristics and returns a shared_ptr to that
+   * UpDownCounter.
+   *
+   * @param name the name of the new UpDownCounter.
+   * @param description a brief description of what the UpDownCounter is used for.
+   * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
+   * @param enabled a boolean value that turns on or off the metric instrument.
+   * @return a shared pointer to the created UpDownCounter.
+   */
+  virtual nostd::shared_ptr<UpDownCounter<short>> CreateShortUpDownCounter(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit = "",
+      const bool enabled = true) = 0;
+
+  virtual nostd::shared_ptr<UpDownCounter<int>> CreateIntUpDownCounter(nostd::string_view name,
+                                                                    nostd::string_view description = "",
+                                                                    nostd::string_view unit = "",
+                                                                    const bool enabled = true) = 0;
+
+  virtual nostd::shared_ptr<UpDownCounter<float>> CreateFloatUpDownCounter(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit = "",
+      const bool enabled = true) = 0;
+
+  virtual nostd::shared_ptr<UpDownCounter<double>> CreateDoubleUpDownCounter(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit = "",
+      const bool enabled = true) = 0;
+
+/**
+   * Creates a Asynchronouse (Observable) UpDownCounter with the passed characteristics and returns a shared_ptr to that
+   * Observable UpDownCounter
+   *
+   * @param name the name of the new Observable UpDownCounter.
+   * @param description a brief description of what the Observable UpDownCounter is used for.
+   * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
+   * @param enabled a boolean value that turns on or off the metric instrument.
+   * @param callback the function to be observed by the instrument.
+   * @return a shared pointer to the created Observable UpDownCounter.
+   */
+  virtual nostd::shared_ptr<ObservableUpDownCounter<short>> CreateShortObservableUpDownCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<short>),
+      nostd::string_view description = "",
+      nostd::string_view unit = "",
+      const bool enabled = true
+      ) = 0;
+
+  virtual nostd::shared_ptr<ObservableUpDownCounter<int>> CreateIntObservableUpDownCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<int>),
+      nostd::string_view description = "",
+      nostd::string_view unit = "",
+      const bool enabled = true,
+      ) = 0;
+
+  virtual nostd::shared_ptr<ObservableUpDownCounter<float>> CreateFloatObservableUpDownCounter(
+      nostd::string_view name,
+      nostd::string_view description,
+      nostd::string_view unit,
+      const bool enabled,
+      void (*callback)(ObserverResult<float>)) = 0;
+
+  virtual nostd::shared_ptr<ObservableUpDownCounter<double>> CreateDoubleObservableUpDownCounter(
+      nostd::string_view name,
+      nostd::string_view description,
+      nostd::string_view unit,
+      const bool enabled,
+      void (*callback)(ObserverResult<double>)) = 0;
+
+  /**
+   * Utility method that allows users to atomically record measurements to a set of
+   * synchronous metric instruments with a common set of labels.
+   *
+   * @param labels the set of labels to associate with this recorder.
+   * @param instruments a span of pointers to the instruments to record to.
+   * @param values a span of values to record to the instruments in the corresponding
+   * position in the instruments span.
+   */
+  virtual void RecordShortBatch(const common::KeyValueIterable &labels,
+                                nostd::span<SynchronousInstrument<short> *> instruments,
+                                nostd::span<const short> values) noexcept = 0;
+
+  virtual void RecordIntBatch(const common::KeyValueIterable &labels,
+                              nostd::span<SynchronousInstrument<int> *> instruments,
+                              nostd::span<const int> values) noexcept = 0;
+
+  virtual void RecordFloatBatch(const common::KeyValueIterable &labels,
+                                nostd::span<SynchronousInstrument<float> *> instruments,
+                                nostd::span<const float> values) noexcept = 0;
+
+  virtual void RecordDoubleBatch(const common::KeyValueIterable &labels,
+                                 nostd::span<SynchronousInstrument<double> *> instruments,
+                                 nostd::span<const double> values) noexcept = 0;
+};
+}  // namespace metrics
+OPENTELEMETRY_END_NAMESPACE
+#endif
diff --git a/api/include/opentelemetry/metrics_new/meter_provider.h b/api/include/opentelemetry/metrics_new/meter_provider.h
new file mode 100644
index 0000000000..8d57f6d201
--- /dev/null
+++ b/api/include/opentelemetry/metrics_new/meter_provider.h
@@ -0,0 +1,33 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#pragma once
+#ifdef ENABLE_METRICS_PREVIEW
+
+#  include "opentelemetry/metrics/meter.h"
+#  include "opentelemetry/nostd/shared_ptr.h"
+#  include "opentelemetry/nostd/string_view.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace metrics_new
+{
+/**
+ * Creates new Meter instances.
+ */
+class MeterProvider
+{
+public:
+  virtual ~MeterProvider() = default;
+  /**
+   * Gets or creates a named Meter instance.
+   *
+   * Optionally a version can be passed to create a named and versioned Meter
+   * instance.
+   */
+  virtual nostd::shared_ptr<Meter> GetMeter(nostd::string_view library_name,
+                                            nostd::string_view library_version = "",
+                                            nostd::string_view schema_url      = "") = 0;) = 0;
+};
+}  // namespace metrics
+OPENTELEMETRY_END_NAMESPACE
+#endif
diff --git a/api/include/opentelemetry/metrics_new/observer_result.h b/api/include/opentelemetry/metrics_new/observer_result.h
new file mode 100644
index 0000000000..90ad10efc2
--- /dev/null
+++ b/api/include/opentelemetry/metrics_new/observer_result.h
@@ -0,0 +1,41 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#pragma once
+#ifdef ENABLE_METRICS_PREVIEW
+
+#  include "instrument.h"
+#  include "opentelemetry/nostd/shared_ptr.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace metrics
+{
+
+/**
+ * ObserverResult class is necessary for the callback recording asynchronous
+ * instrument use.  Callback functions asynchronous instruments are designed to
+ * accept a single ObserverResult object and update using its pointer to the
+ * instrument itself.
+ */
+
+template <class T>
+class ObserverResult
+{
+
+public:
+  ObserverResult() = default;
+
+  ObserverResult(AsynchronousInstrument<T> *instrument) : instrument_(instrument) {}
+
+  virtual void observe(T value, const common::KeyValueIterable &labels)
+  {
+    instrument_->observe(value, labels);
+  }
+
+private:
+  AsynchronousInstrument<T> *instrument_;
+};
+
+}  // namespace metrics
+OPENTELEMETRY_END_NAMESPACE
+#endif
diff --git a/api/include/opentelemetry/metrics_new/provider.h b/api/include/opentelemetry/metrics_new/provider.h
new file mode 100644
index 0000000000..5c350c2147
--- /dev/null
+++ b/api/include/opentelemetry/metrics_new/provider.h
@@ -0,0 +1,59 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#pragma once
+#ifdef ENABLE_METRICS_PREVIEW
+#  include <mutex>
+
+#  include "opentelemetry/common/spin_lock_mutex.h"
+#  include "opentelemetry/metrics/meter_provider.h"
+#  include "opentelemetry/metrics/noop.h"
+#  include "opentelemetry/nostd/shared_ptr.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace metrics_new
+{
+/**
+ * Stores the singleton global MeterProvider.
+ */
+class Provider
+{
+public:
+  /**
+   * Returns the singleton MeterProvider.
+   *
+   * By default, a no-op MeterProvider is returned. This will never return a
+   * nullptr MeterProvider.
+   */
+  static nostd::shared_ptr<MeterProvider> GetMeterProvider() noexcept
+  {
+    std::lock_guard<common::SpinLockMutex> guard(GetLock());
+    return nostd::shared_ptr<MeterProvider>(GetProvider());
+  }
+
+  /**
+   * Changes the singleton MeterProvider.
+   */
+  static void SetMeterProvider(nostd::shared_ptr<MeterProvider> tp) noexcept
+  {
+    std::lock_guard<common::SpinLockMutex> guard(GetLock());
+    GetProvider() = tp;
+  }
+
+private:
+  static nostd::shared_ptr<MeterProvider> &GetProvider() noexcept
+  {
+    static nostd::shared_ptr<MeterProvider> provider(new NoopMeterProvider);
+    return provider;
+  }
+
+  static common::SpinLockMutex &GetLock() noexcept
+  {
+    static common::SpinLockMutex lock;
+    return lock;
+  }
+};
+
+}  // namespace metrics
+OPENTELEMETRY_END_NAMESPACE
+#endif
diff --git a/api/include/opentelemetry/metrics_new/sync_instruments.h b/api/include/opentelemetry/metrics_new/sync_instruments.h
new file mode 100644
index 0000000000..0150ece1f0
--- /dev/null
+++ b/api/include/opentelemetry/metrics_new/sync_instruments.h
@@ -0,0 +1,87 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#pragma once
+#ifdef ENABLE_METRICS_PREVIEW
+
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace metrics_new
+{
+
+template <class T>
+class Counter 
+{
+
+public:
+
+  /**
+   * Add adds the value to the counter's sum
+   *
+   * @param value The increment amount. MUST be non-negative.
+   */
+  virtual void add(T value ) = 0;
+
+  /**
+   * Add adds the value to the counter's sum. The labels should contain
+   * the keys and values to be associated with this value.  Counters only     
+   * accept positive valued updates.
+   *
+   * @param value The increment amount. MUST be non-negative.
+   * @param labels the set of labels, as key-value pairs
+   */
+
+  virtual void add(T value, const common::KeyValueIterable &labels) = 0;
+
+};
+
+/** A histogram instrument that records values. */
+
+template <class T>
+class Historgram
+{
+  public:
+
+  /**
+   * Records a value.
+   *
+   * @param value The increment amount. May be positive, negative or zero.
+   */ 
+  virtual void record(T value) = 0;
+
+  /**
+   * Records a value with a set of attributes.
+   *
+   * @param value The increment amount. May be positive, negative or zero.
+   * @param attributes A set of attributes to associate with the count.
+   */
+   void record(T value, const common::KeyValueIterable &labels) = 0;
+
+}
+
+/** An up-down-counter instrument that adds or reduce values. */
+
+template <class T>
+class UpDownCounter
+{
+  public:
+  /**
+   * Adds a value.
+   *
+   * @param value The amount of the measurement.
+   */ 
+  virtual void add(T value) = 0;
+
+  /**
+   * Add a value with a set of attributes.
+   *
+   * @param value The increment amount. May be positive, negative or zero.
+   * @param attributes A set of attributes to associate with the count.
+   */
+   void add(T value, const common::KeyValueIterable &labels) = 0;
+
+};
+
+}  // namespace metrics
+OPENTELEMETRY_END_NAMESPACE
+#endif

From e8674e2362b5c024f0135367304c5be916d87730 Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Mon, 25 Oct 2021 08:49:47 -0700
Subject: [PATCH 02/14] initial commit for async instruments

---
 .../metrics_new/async_instruments.h           | 78 +++----------------
 1 file changed, 10 insertions(+), 68 deletions(-)

diff --git a/api/include/opentelemetry/metrics_new/async_instruments.h b/api/include/opentelemetry/metrics_new/async_instruments.h
index 867382ec19..426f109839 100644
--- a/api/include/opentelemetry/metrics_new/async_instruments.h
+++ b/api/include/opentelemetry/metrics_new/async_instruments.h
@@ -8,81 +8,23 @@
 #  include "observer_result.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
-namespace metrics
+namespace metrics_new
 {
+class AsynchronousInstrument
+{};
 
 template <class T>
-class ValueObserver : virtual public AsynchronousInstrument<T>
-{
-
-public:
-  ValueObserver() = default;
-
-  ValueObserver(nostd::string_view name,
-                nostd::string_view description,
-                nostd::string_view unit,
-                bool enabled,
-                void (*callback)(ObserverResult<T>))
-  {}
-
-  /*
-   * Updates the instruments aggregator with the new value. The labels should
-   * contain the keys and values to be associated with this value.
-   *
-   * @param value is the numerical representation of the metric being captured
-   * @param labels the set of labels, as key-value pairs
-   */
-  virtual void observe(T value, const common::KeyValueIterable &labels) override = 0;
-
-  /**
-   * Captures data by activating the callback function associated with the
-   * instrument and storing its return value.  Callbacks for asynchronous
-   * instruments are defined during construction.
-   *
-   * @param none
-   * @return none
-   */
-  virtual void run() override = 0;
-};
+class ObservableCounter : public AsynchronousInstrument
+{};
 
 template <class T>
-class SumObserver : virtual public AsynchronousInstrument<T>
-{
-
-public:
-  SumObserver() = default;
-
-  SumObserver(nostd::string_view name,
-              nostd::string_view description,
-              nostd::string_view unit,
-              bool enabled,
-              void (*callback)(ObserverResult<T>))
-  {}
-
-  virtual void observe(T value, const common::KeyValueIterable &labels) override = 0;
-
-  virtual void run() override = 0;
-};
+class ObservableGauge : public AsynchronousInstrument
+{};
 
 template <class T>
-class UpDownSumObserver : virtual public AsynchronousInstrument<T>
-{
-
-public:
-  UpDownSumObserver() = default;
-
-  UpDownSumObserver(nostd::string_view name,
-                    nostd::string_view description,
-                    nostd::string_view unit,
-                    bool enabled,
-                    void (*callback)(ObserverResult<T>))
-  {}
-
-  virtual void observe(T value, const common::KeyValueIterable &labels) override = 0;
-
-  virtual void run() override = 0;
-};
+class ObservableUpDownCounter : public AsynchronousInstrument
+{};
 
-}  // namespace metrics
+}  // namespace metrics_new
 OPENTELEMETRY_END_NAMESPACE
 #endif

From 4a829a0b28ca18db0b73be32e9814a80e02b6a10 Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Mon, 25 Oct 2021 08:52:00 -0700
Subject: [PATCH 03/14] format

---
 api/include/opentelemetry/metrics_new/meter.h | 186 ++++++++----------
 .../metrics_new/meter_provider.h              |   3 +-
 .../metrics_new/observer_result.h             |  24 +--
 .../opentelemetry/metrics_new/provider.h      |   2 +-
 .../metrics_new/sync_instruments.h            |  38 ++--
 5 files changed, 108 insertions(+), 145 deletions(-)

diff --git a/api/include/opentelemetry/metrics_new/meter.h b/api/include/opentelemetry/metrics_new/meter.h
index 9712275de5..1219a61024 100644
--- a/api/include/opentelemetry/metrics_new/meter.h
+++ b/api/include/opentelemetry/metrics_new/meter.h
@@ -40,29 +40,32 @@ class Meter
    * @throws IllegalArgumentException if a different metric by the same name exists in this meter.
    * @throws IllegalArgumentException if the {@code name} does not match spec requirements.
    */
-  virtual nostd::shared_ptr<Counter<short>> CreateShortCounter(nostd::string_view name,
-                                                            nostd::string_view description = "",
-                                                            nostd::string_view unit = "",
-                                                            const bool enabled = true) = 0;
+  virtual nostd::shared_ptr<Counter<short>> CreateShortCounter(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "",
+      const bool enabled             = true) noexcept = 0;
 
   virtual nostd::shared_ptr<Counter<int>> CreateIntCounter(nostd::string_view name,
-                                                        nostd::string_view description = "",
-                                                        nostd::string_view unit = "",
-                                                        const bool enabled = true) = 0;
+                                                           nostd::string_view description = "",
+                                                           nostd::string_view unit        = "",
+                                                           const bool enabled = true) noexcept = 0;
 
-  virtual nostd::shared_ptr<Counter<float>> CreateFloatCounter(nostd::string_view name,
-                                                            nostd::string_view description = "",
-                                                            nostd::string_view unit = "",
-                                                            const bool enabled = true) = 0;
+  virtual nostd::shared_ptr<Counter<float>> CreateFloatCounter(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "",
+      const bool enabled             = true) noexcept = 0;
 
-  virtual nostd::shared_ptr<Counter<double>> CreateDoubleCounter(nostd::string_view name,
-                                                              nostd::string_view description = "",
-                                                              nostd::string_view unit = "",
-                                                              const bool enabled = true) = 0;
+  virtual nostd::shared_ptr<Counter<double>> CreateDoubleCounter(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "",
+      const bool enabled             = true) noexcept = 0;
 
-/**
-   * Creates a Asynchronouse (Observable) counter with the passed characteristics and returns a shared_ptr to that
-   * Observable Counter
+  /**
+   * Creates a Asynchronouse (Observable) counter with the passed characteristics and returns a
+   * shared_ptr to that Observable Counter
    *
    * @param name the name of the new Observable Counter.
    * @param description a brief description of what the Observable Counter is used for.
@@ -75,31 +78,29 @@ class Meter
       nostd::string_view name,
       void (*callback)(ObserverResult<short>),
       nostd::string_view description = "",
-      nostd::string_view unit = "",
-      const bool enabled = true
-      ) = 0;
+      nostd::string_view unit        = "",
+      const bool enabled             = true) noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableCounter<int>> CreateIntObservableCounter(
       nostd::string_view name,
       void (*callback)(ObserverResult<int>),
       nostd::string_view description = "",
-      nostd::string_view unit = "",
-      const bool enabled = true,
-      ) = 0;
+      nostd::string_view unit        = "",
+      const bool enabled             = true, ) noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableCounter<float>> CreateFloatObservableCounter(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit = "",
-      const bool enabled = true,
-      void (*callback)(ObserverResult<float>)) = 0;
+      nostd::string_view unit        = "",
+      const bool enabled             = true,
+      void (*callback)(ObserverResult<float>)) noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableCounter<double>> CreateDoubleObservableCounter(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit = "",
-      const bool enabled = true,
-      void (*callback)(ObserverResult<double>)) = 0;
+      nostd::string_view unit        = "",
+      const bool enabled             = true,
+      void (*callback)(ObserverResult<double>)) noexcept = 0;
 
   /**
    * Creates a Histogram with the passed characteristics and returns a shared_ptr to that Histogram.
@@ -110,30 +111,33 @@ class Meter
    * @param enabled a boolean value that turns on or off the metric instrument.
    * @return a shared pointer to the created Histogram.
    */
-  virtual nostd::shared_ptr<Histogram<short>> CreateShortHistogram(nostd::string_view name,
-                                                            nostd::string_view description = "",
-                                                            nostd::string_view unit = "",
-                                                            const bool enabled = true) = 0;
-
-  virtual nostd::shared_ptr<Histogram<int>> CreateIntHistogram(nostd::string_view name,
-                                                        nostd::string_view description = "",
-                                                        nostd::string_view unit = "",
-                                                        const bool enabled = true) = 0;
+  virtual nostd::shared_ptr<Histogram<short>> CreateShortHistogram(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "",
+      const bool enabled             = true) noexcept = 0;
 
-  virtual nostd::shared_ptr<Histogram<float>> CreateFloatHistogram(nostd::string_view name,
-                                                            nostd::string_view description = "",
-                                                            nostd::string_view unit = "",
-                                                            const bool enabled = true) = 0;
+  virtual nostd::shared_ptr<Histogram<int>> CreateIntHistogram(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "",
+      const bool enabled             = true) noexcept = 0;
 
-  virtual nostd::shared_ptr<Histogram<double>> CreateDoubleHistogram(nostd::string_view name,
-                                                              nostd::string_view description = "",
-                                                              nostd::string_view unit = "",
-                                                              const bool enabled = true) = 0;
+  virtual nostd::shared_ptr<Histogram<float>> CreateFloatHistogram(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "",
+      const bool enabled             = true) noexcept = 0;
 
+  virtual nostd::shared_ptr<Histogram<double>> CreateDoubleHistogram(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "",
+      const bool enabled             = true) noexcept = 0;
 
-/**
-   * Creates a Asynchronouse (Observable) Gauge with the passed characteristics and returns a shared_ptr to that
-   * Observable Counter
+  /**
+   * Creates a Asynchronouse (Observable) Gauge with the passed characteristics and returns a
+   * shared_ptr to that Observable Counter
    *
    * @param name the name of the new Observable Gauge.
    * @param description a brief description of what the Observable Gauge is used for.
@@ -146,31 +150,29 @@ class Meter
       nostd::string_view name,
       void (*callback)(ObserverResult<short>),
       nostd::string_view description = "",
-      nostd::string_view unit = "",
-      const bool enabled = true
-      ) = 0;
+      nostd::string_view unit        = "",
+      const bool enabled             = true) noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableGauge<int>> CreateIntObservableGauge(
       nostd::string_view name,
       void (*callback)(ObserverResult<int>),
       nostd::string_view description = "",
-      nostd::string_view unit = "",
-      const bool enabled = true,
-      ) = 0;
+      nostd::string_view unit        = "",
+      const bool enabled             = true, ) noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableGauge<float>> CreateFloatObservableGauge(
       nostd::string_view name,
       nostd::string_view description,
       nostd::string_view unit,
       const bool enabled,
-      void (*callback)(ObserverResult<float>)) = 0;
+      void (*callback)(ObserverResult<float>)) noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableGauge<double>> CreateDoubleObservableGauge(
       nostd::string_view name,
       nostd::string_view description,
       nostd::string_view unit,
       const bool enabled,
-      void (*callback)(ObserverResult<double>)) = 0;
+      void (*callback)(ObserverResult<double>)) noexcept = 0;
 
   /**
    * Creates an UpDownCounter with the passed characteristics and returns a shared_ptr to that
@@ -185,29 +187,30 @@ class Meter
   virtual nostd::shared_ptr<UpDownCounter<short>> CreateShortUpDownCounter(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit = "",
-      const bool enabled = true) = 0;
+      nostd::string_view unit        = "",
+      const bool enabled             = true) noexcept = 0;
 
-  virtual nostd::shared_ptr<UpDownCounter<int>> CreateIntUpDownCounter(nostd::string_view name,
-                                                                    nostd::string_view description = "",
-                                                                    nostd::string_view unit = "",
-                                                                    const bool enabled = true) = 0;
+  virtual nostd::shared_ptr<UpDownCounter<int>> CreateIntUpDownCounter(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "",
+      const bool enabled             = true) = 0;
 
   virtual nostd::shared_ptr<UpDownCounter<float>> CreateFloatUpDownCounter(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit = "",
-      const bool enabled = true) = 0;
+      nostd::string_view unit        = "",
+      const bool enabled             = true) noexcept = 0;
 
   virtual nostd::shared_ptr<UpDownCounter<double>> CreateDoubleUpDownCounter(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit = "",
-      const bool enabled = true) = 0;
+      nostd::string_view unit        = "",
+      const bool enabled             = true) noexcept = 0;
 
-/**
-   * Creates a Asynchronouse (Observable) UpDownCounter with the passed characteristics and returns a shared_ptr to that
-   * Observable UpDownCounter
+  /**
+   * Creates a Asynchronouse (Observable) UpDownCounter with the passed characteristics and returns
+   * a shared_ptr to that Observable UpDownCounter
    *
    * @param name the name of the new Observable UpDownCounter.
    * @param description a brief description of what the Observable UpDownCounter is used for.
@@ -220,57 +223,30 @@ class Meter
       nostd::string_view name,
       void (*callback)(ObserverResult<short>),
       nostd::string_view description = "",
-      nostd::string_view unit = "",
-      const bool enabled = true
-      ) = 0;
+      nostd::string_view unit        = "",
+      const bool enabled             = true) noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableUpDownCounter<int>> CreateIntObservableUpDownCounter(
       nostd::string_view name,
       void (*callback)(ObserverResult<int>),
       nostd::string_view description = "",
-      nostd::string_view unit = "",
-      const bool enabled = true,
-      ) = 0;
+      nostd::string_view unit        = "",
+      const bool enabled             = true, ) noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableUpDownCounter<float>> CreateFloatObservableUpDownCounter(
       nostd::string_view name,
       nostd::string_view description,
       nostd::string_view unit,
       const bool enabled,
-      void (*callback)(ObserverResult<float>)) = 0;
+      void (*callback)(ObserverResult<float>)) noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableUpDownCounter<double>> CreateDoubleObservableUpDownCounter(
       nostd::string_view name,
       nostd::string_view description,
       nostd::string_view unit,
       const bool enabled,
-      void (*callback)(ObserverResult<double>)) = 0;
-
-  /**
-   * Utility method that allows users to atomically record measurements to a set of
-   * synchronous metric instruments with a common set of labels.
-   *
-   * @param labels the set of labels to associate with this recorder.
-   * @param instruments a span of pointers to the instruments to record to.
-   * @param values a span of values to record to the instruments in the corresponding
-   * position in the instruments span.
-   */
-  virtual void RecordShortBatch(const common::KeyValueIterable &labels,
-                                nostd::span<SynchronousInstrument<short> *> instruments,
-                                nostd::span<const short> values) noexcept = 0;
-
-  virtual void RecordIntBatch(const common::KeyValueIterable &labels,
-                              nostd::span<SynchronousInstrument<int> *> instruments,
-                              nostd::span<const int> values) noexcept = 0;
-
-  virtual void RecordFloatBatch(const common::KeyValueIterable &labels,
-                                nostd::span<SynchronousInstrument<float> *> instruments,
-                                nostd::span<const float> values) noexcept = 0;
-
-  virtual void RecordDoubleBatch(const common::KeyValueIterable &labels,
-                                 nostd::span<SynchronousInstrument<double> *> instruments,
-                                 nostd::span<const double> values) noexcept = 0;
+      void (*callback)(ObserverResult<double>)) noexcept = 0;
 };
-}  // namespace metrics
+}  // namespace metrics_new
 OPENTELEMETRY_END_NAMESPACE
 #endif
diff --git a/api/include/opentelemetry/metrics_new/meter_provider.h b/api/include/opentelemetry/metrics_new/meter_provider.h
index 8d57f6d201..8bd2c590f2 100644
--- a/api/include/opentelemetry/metrics_new/meter_provider.h
+++ b/api/include/opentelemetry/metrics_new/meter_provider.h
@@ -26,8 +26,7 @@ class MeterProvider
    */
   virtual nostd::shared_ptr<Meter> GetMeter(nostd::string_view library_name,
                                             nostd::string_view library_version = "",
-                                            nostd::string_view schema_url      = "") = 0;) = 0;
-};
+                                            nostd::string_view schema_url      = "") noexcept = 0;
 }  // namespace metrics
 OPENTELEMETRY_END_NAMESPACE
 #endif
diff --git a/api/include/opentelemetry/metrics_new/observer_result.h b/api/include/opentelemetry/metrics_new/observer_result.h
index 90ad10efc2..0533e21a31 100644
--- a/api/include/opentelemetry/metrics_new/observer_result.h
+++ b/api/include/opentelemetry/metrics_new/observer_result.h
@@ -3,19 +3,15 @@
 
 #pragma once
 #ifdef ENABLE_METRICS_PREVIEW
-
-#  include "instrument.h"
-#  include "opentelemetry/nostd/shared_ptr.h"
+#  include "c
 
 OPENTELEMETRY_BEGIN_NAMESPACE
-namespace metrics
+namespace metrics_new
 {
 
 /**
  * ObserverResult class is necessary for the callback recording asynchronous
- * instrument use.  Callback functions asynchronous instruments are designed to
- * accept a single ObserverResult object and update using its pointer to the
- * instrument itself.
+ * instrument use.
  */
 
 template <class T>
@@ -23,19 +19,11 @@ class ObserverResult
 {
 
 public:
-  ObserverResult() = default;
-
-  ObserverResult(AsynchronousInstrument<T> *instrument) : instrument_(instrument) {}
-
-  virtual void observe(T value, const common::KeyValueIterable &labels)
-  {
-    instrument_->observe(value, labels);
-  }
+  virtual void observe(T value) noexcept = 0;
 
-private:
-  AsynchronousInstrument<T> *instrument_;
+  virtual void observer(T value, const common::KeyValueIterable &labels) noexcept = 0;
 };
 
-}  // namespace metrics
+}  // namespace metrics_new
 OPENTELEMETRY_END_NAMESPACE
 #endif
diff --git a/api/include/opentelemetry/metrics_new/provider.h b/api/include/opentelemetry/metrics_new/provider.h
index 5c350c2147..27c14c0489 100644
--- a/api/include/opentelemetry/metrics_new/provider.h
+++ b/api/include/opentelemetry/metrics_new/provider.h
@@ -54,6 +54,6 @@ class Provider
   }
 };
 
-}  // namespace metrics
+}  // namespace metrics_new
 OPENTELEMETRY_END_NAMESPACE
 #endif
diff --git a/api/include/opentelemetry/metrics_new/sync_instruments.h b/api/include/opentelemetry/metrics_new/sync_instruments.h
index 0150ece1f0..cd1a1fad87 100644
--- a/api/include/opentelemetry/metrics_new/sync_instruments.h
+++ b/api/include/opentelemetry/metrics_new/sync_instruments.h
@@ -4,50 +4,51 @@
 #pragma once
 #ifdef ENABLE_METRICS_PREVIEW
 
+#  include "opentelemetry/common/key_value_iterable.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
 namespace metrics_new
 {
 
+class SynchronousInstrument
+{};
+
 template <class T>
-class Counter 
+class Counter : public SynchronousInstrument
 {
 
 public:
-
   /**
    * Add adds the value to the counter's sum
    *
    * @param value The increment amount. MUST be non-negative.
    */
-  virtual void add(T value ) = 0;
+  virtual void add(T value) noexcept = 0;
 
   /**
    * Add adds the value to the counter's sum. The labels should contain
-   * the keys and values to be associated with this value.  Counters only     
+   * the keys and values to be associated with this value.  Counters only
    * accept positive valued updates.
    *
    * @param value The increment amount. MUST be non-negative.
    * @param labels the set of labels, as key-value pairs
    */
 
-  virtual void add(T value, const common::KeyValueIterable &labels) = 0;
-
+  virtual void add(T value, const common::KeyValueIterable &labels) noexcept = 0;
 };
 
 /** A histogram instrument that records values. */
 
 template <class T>
-class Historgram
+class Historgram : public SynchronousInstrument
 {
-  public:
-
+public:
   /**
    * Records a value.
    *
    * @param value The increment amount. May be positive, negative or zero.
-   */ 
-  virtual void record(T value) = 0;
+   */
+  virtual void record(T value) noexcept = 0;
 
   /**
    * Records a value with a set of attributes.
@@ -55,22 +56,22 @@ class Historgram
    * @param value The increment amount. May be positive, negative or zero.
    * @param attributes A set of attributes to associate with the count.
    */
-   void record(T value, const common::KeyValueIterable &labels) = 0;
+  void record(T value, const common::KeyValueIterable &labels) noexcept = 0;
 
 }
 
 /** An up-down-counter instrument that adds or reduce values. */
 
 template <class T>
-class UpDownCounter
+class UpDownCounter : public SynchronousInstrument
 {
-  public:
+public:
   /**
    * Adds a value.
    *
    * @param value The amount of the measurement.
-   */ 
-  virtual void add(T value) = 0;
+   */
+  virtual void add(T value) noexcept = 0;
 
   /**
    * Add a value with a set of attributes.
@@ -78,10 +79,9 @@ class UpDownCounter
    * @param value The increment amount. May be positive, negative or zero.
    * @param attributes A set of attributes to associate with the count.
    */
-   void add(T value, const common::KeyValueIterable &labels) = 0;
-
+  void add(T value, const common::KeyValueIterable &labels) noexcept = 0;
 };
 
-}  // namespace metrics
+}  // namespace metrics_new
 OPENTELEMETRY_END_NAMESPACE
 #endif

From d0d6131b8f1bc5c4eed465a1f84cf9516471785e Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Mon, 25 Oct 2021 13:21:43 -0700
Subject: [PATCH 04/14] review comments

---
 CMakeLists.txt                                | 21 +++++++++++++++++++
 .../metrics_new/observer_result.h             |  2 +-
 .../metrics_new/sync_instruments.h            | 10 ++++-----
 3 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 272e10927b..1f2c86471d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -165,6 +165,8 @@ option(WITH_NO_GETENV "Whether the platform supports environment variables" OFF)
 
 option(BUILD_TESTING "Whether to enable tests" ON)
 
+option(BUILD_PACKAGE "Whether to build rpm/deb package" OFF)
+
 if(WITH_NO_GENENV)
   add_definitions(-DNO_GETENV)
 endif()
@@ -412,3 +414,22 @@ install(
   EXPORT "${PROJECT_NAME}-target"
   NAMESPACE "${PROJECT_NAME}::"
   DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}")
+
+if(BUILD_PACKAGE AND UNIX)
+  execute_process(
+    COMMAND lsb_release -si
+    OUTPUT_VARIABLE distribution
+    OUTPUT_STRIP_TRAILING_WHITESPACE)
+  if(distribution STREQUAL "Debian" OR distribution STREQUAL "Ubuntu")
+    set(INSTALL_LIB_DIR
+        ${CMAKE_INSTALL_PREFIX}/lib/${CPACK_DEBIAN_ARCHITECTURE}-linux-gnu)
+    include(cmake/MakeDeb.cmake)
+  elseif(
+    distribution MATCHES "RedHat.*"
+    OR distribution MATCHES "openSUSE.*"
+    OR distribution STREQUAL "Fedora")
+    set(INSTALL_LIB_DIR
+        ${CMAKE_INSTALL_PREFIX}/lib/${CMAKE_SYSTEM_PROCESSOR}-linux-gnu)
+    include(cmake/MakeRpm.cmake)
+  endif()
+endif()
diff --git a/api/include/opentelemetry/metrics_new/observer_result.h b/api/include/opentelemetry/metrics_new/observer_result.h
index 0533e21a31..f668760db8 100644
--- a/api/include/opentelemetry/metrics_new/observer_result.h
+++ b/api/include/opentelemetry/metrics_new/observer_result.h
@@ -21,7 +21,7 @@ class ObserverResult
 public:
   virtual void observe(T value) noexcept = 0;
 
-  virtual void observer(T value, const common::KeyValueIterable &labels) noexcept = 0;
+  virtual void observer(T value, const common::KeyValueIterable &attributes) noexcept = 0;
 };
 
 }  // namespace metrics_new
diff --git a/api/include/opentelemetry/metrics_new/sync_instruments.h b/api/include/opentelemetry/metrics_new/sync_instruments.h
index cd1a1fad87..a8b14394b3 100644
--- a/api/include/opentelemetry/metrics_new/sync_instruments.h
+++ b/api/include/opentelemetry/metrics_new/sync_instruments.h
@@ -26,15 +26,15 @@ class Counter : public SynchronousInstrument
   virtual void add(T value) noexcept = 0;
 
   /**
-   * Add adds the value to the counter's sum. The labels should contain
+   * Add adds the value to the counter's sum. The attributes should contain
    * the keys and values to be associated with this value.  Counters only
    * accept positive valued updates.
    *
    * @param value The increment amount. MUST be non-negative.
-   * @param labels the set of labels, as key-value pairs
+   * @param attributes the set of attributes, as key-value pairs
    */
 
-  virtual void add(T value, const common::KeyValueIterable &labels) noexcept = 0;
+  virtual void add(T value, const common::KeyValueIterable &attributes) noexcept = 0;
 };
 
 /** A histogram instrument that records values. */
@@ -56,7 +56,7 @@ class Historgram : public SynchronousInstrument
    * @param value The increment amount. May be positive, negative or zero.
    * @param attributes A set of attributes to associate with the count.
    */
-  void record(T value, const common::KeyValueIterable &labels) noexcept = 0;
+  void record(T value, const common::KeyValueIterable &attributes) noexcept = 0;
 
 }
 
@@ -79,7 +79,7 @@ class UpDownCounter : public SynchronousInstrument
    * @param value The increment amount. May be positive, negative or zero.
    * @param attributes A set of attributes to associate with the count.
    */
-  void add(T value, const common::KeyValueIterable &labels) noexcept = 0;
+  void add(T value, const common::KeyValueIterable &attributes) noexcept = 0;
 };
 
 }  // namespace metrics_new

From 7f47b1e796ed1534240dc251e08ac0cadbf4a35f Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Mon, 25 Oct 2021 14:59:53 -0700
Subject: [PATCH 05/14] overload sync instruement

---
 .../metrics_new/async_instruments.h           |  5 +-
 api/include/opentelemetry/metrics_new/meter.h | 19 ++----
 .../metrics_new/meter_provider.h              |  8 +--
 .../metrics_new/observer_result.h             | 26 ++++++--
 .../opentelemetry/metrics_new/provider.h      | 14 ++--
 .../metrics_new/sync_instruments.h            | 64 ++++++++++++++++---
 6 files changed, 95 insertions(+), 41 deletions(-)

diff --git a/api/include/opentelemetry/metrics_new/async_instruments.h b/api/include/opentelemetry/metrics_new/async_instruments.h
index 426f109839..143206789e 100644
--- a/api/include/opentelemetry/metrics_new/async_instruments.h
+++ b/api/include/opentelemetry/metrics_new/async_instruments.h
@@ -2,10 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #pragma once
-#ifdef ENABLE_METRICS_PREVIEW
 
-#  include "instrument.h"
-#  include "observer_result.h"
+#include "instrument.h"
+#include "observer_result.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
 namespace metrics_new
diff --git a/api/include/opentelemetry/metrics_new/meter.h b/api/include/opentelemetry/metrics_new/meter.h
index 1219a61024..65b5f065db 100644
--- a/api/include/opentelemetry/metrics_new/meter.h
+++ b/api/include/opentelemetry/metrics_new/meter.h
@@ -2,15 +2,14 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #pragma once
-#ifdef ENABLE_METRICS_PREVIEW
 
-#  include "opentelemetry/metrics_new/async_instruments.h"
-#  include "opentelemetry/metrics_new/instrument.h"
-#  include "opentelemetry/metrics_new/sync_instruments.h"
-#  include "opentelemetry/nostd/shared_ptr.h"
-#  include "opentelemetry/nostd/span.h"
-#  include "opentelemetry/nostd/string_view.h"
-#  include "opentelemetry/version.h"
+#include "opentelemetry/metrics_new/async_instruments.h"
+#include "opentelemetry/metrics_new/instrument.h"
+#include "opentelemetry/metrics_new/sync_instruments.h"
+#include "opentelemetry/nostd/shared_ptr.h"
+#include "opentelemetry/nostd/span.h"
+#include "opentelemetry/nostd/string_view.h"
+#include "opentelemetry/version.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
 namespace metrics_new
@@ -36,9 +35,6 @@ class Meter
    * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
    * @param enabled a boolean value that turns on or off the metric instrument.
    * @return a shared pointer to the created Counter.
-   * @throws NullPointerException if {@code name} is null
-   * @throws IllegalArgumentException if a different metric by the same name exists in this meter.
-   * @throws IllegalArgumentException if the {@code name} does not match spec requirements.
    */
   virtual nostd::shared_ptr<Counter<short>> CreateShortCounter(
       nostd::string_view name,
@@ -249,4 +245,3 @@ class Meter
 };
 }  // namespace metrics_new
 OPENTELEMETRY_END_NAMESPACE
-#endif
diff --git a/api/include/opentelemetry/metrics_new/meter_provider.h b/api/include/opentelemetry/metrics_new/meter_provider.h
index 8bd2c590f2..e5579694ce 100644
--- a/api/include/opentelemetry/metrics_new/meter_provider.h
+++ b/api/include/opentelemetry/metrics_new/meter_provider.h
@@ -2,11 +2,10 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #pragma once
-#ifdef ENABLE_METRICS_PREVIEW
 
-#  include "opentelemetry/metrics/meter.h"
-#  include "opentelemetry/nostd/shared_ptr.h"
-#  include "opentelemetry/nostd/string_view.h"
+#include "opentelemetry/metrics/meter.h"
+#include "opentelemetry/nostd/shared_ptr.h"
+#include "opentelemetry/nostd/string_view.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
 namespace metrics_new
@@ -29,4 +28,3 @@ class MeterProvider
                                             nostd::string_view schema_url      = "") noexcept = 0;
 }  // namespace metrics
 OPENTELEMETRY_END_NAMESPACE
-#endif
diff --git a/api/include/opentelemetry/metrics_new/observer_result.h b/api/include/opentelemetry/metrics_new/observer_result.h
index f668760db8..5d78fe2f58 100644
--- a/api/include/opentelemetry/metrics_new/observer_result.h
+++ b/api/include/opentelemetry/metrics_new/observer_result.h
@@ -2,8 +2,10 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #pragma once
-#ifdef ENABLE_METRICS_PREVIEW
-#  include "c
+#include "opentelemetry/common/attribute_value.h"
+#include "opentelemetry/common/key_value_iterable_view.h"
+#include "opentelemetry/nostd/span.h"
+#include "opentelemetry/nostd/string_view.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
 namespace metrics_new
@@ -19,11 +21,25 @@ class ObserverResult
 {
 
 public:
-  virtual void observe(T value) noexcept = 0;
+  virtual void Observe(T value) noexcept = 0;
 
-  virtual void observer(T value, const common::KeyValueIterable &attributes) noexcept = 0;
+  virtual void Observer(T value, const common::KeyValueIterable &attributes) noexcept = 0;
+
+  template <class U,
+            nostd::enable_if_t<common::detail::is_key_value_iterable<U>::value> * = nullptr>
+  void Observe(T value, const U &attributes) noexcept
+  {
+    this->Observe(value, common::KeyValueIterableView<T>{attributes});
+  }
+
+  void Observe(T value,
+               std::initializer_list<std::pair<nostd::string_view, common::AttributeValue>>
+                   attributes) noexcept
+  {
+    this->Observe(value, nostd::span<const std::pair<nostd::string_view, common::AttributeValue>>{
+                             attributes.begin(), attributes.end()});
+  }
 };
 
 }  // namespace metrics_new
 OPENTELEMETRY_END_NAMESPACE
-#endif
diff --git a/api/include/opentelemetry/metrics_new/provider.h b/api/include/opentelemetry/metrics_new/provider.h
index 27c14c0489..aebca3fa73 100644
--- a/api/include/opentelemetry/metrics_new/provider.h
+++ b/api/include/opentelemetry/metrics_new/provider.h
@@ -2,13 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #pragma once
-#ifdef ENABLE_METRICS_PREVIEW
-#  include <mutex>
+#include <mutex>
 
-#  include "opentelemetry/common/spin_lock_mutex.h"
-#  include "opentelemetry/metrics/meter_provider.h"
-#  include "opentelemetry/metrics/noop.h"
-#  include "opentelemetry/nostd/shared_ptr.h"
+#include "opentelemetry/common/spin_lock_mutex.h"
+#include "opentelemetry/metrics/meter_provider.h"
+#include "opentelemetry/metrics/noop.h"
+#include "opentelemetry/nostd/shared_ptr.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
 namespace metrics_new
@@ -55,5 +54,4 @@ class Provider
 };
 
 }  // namespace metrics_new
-OPENTELEMETRY_END_NAMESPACE
-#endif
+OPENTELEMETRY_END_NAMESPACE
\ No newline at end of file
diff --git a/api/include/opentelemetry/metrics_new/sync_instruments.h b/api/include/opentelemetry/metrics_new/sync_instruments.h
index a8b14394b3..bfeab5f95e 100644
--- a/api/include/opentelemetry/metrics_new/sync_instruments.h
+++ b/api/include/opentelemetry/metrics_new/sync_instruments.h
@@ -2,9 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #pragma once
-#ifdef ENABLE_METRICS_PREVIEW
+#ifndef ENABLE_METRICS_PREVIEW
 
-#  include "opentelemetry/common/key_value_iterable.h"
+#  include "opentelemetry/common/attribute_value.h"
+#  include "opentelemetry/common/key_value_iterable_view.h"
+#  include "opentelemetry/nostd/span.h"
+#  include "opentelemetry/nostd/string_view.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
 namespace metrics_new
@@ -23,7 +26,7 @@ class Counter : public SynchronousInstrument
    *
    * @param value The increment amount. MUST be non-negative.
    */
-  virtual void add(T value) noexcept = 0;
+  virtual void Add(T value) noexcept = 0;
 
   /**
    * Add adds the value to the counter's sum. The attributes should contain
@@ -34,7 +37,22 @@ class Counter : public SynchronousInstrument
    * @param attributes the set of attributes, as key-value pairs
    */
 
-  virtual void add(T value, const common::KeyValueIterable &attributes) noexcept = 0;
+  virtual void Add(T value, const common::KeyValueIterable &attributes) noexcept = 0;
+
+  template <class U,
+            nostd::enable_if_t<common::detail::is_key_value_iterable<U>::value> * = nullptr>
+  void Add(T value, const U &attributes) noexcept
+  {
+    this->Add(value, common::KeyValueIterableView<T>{attributes});
+  }
+
+  void Add(T value,
+           std::initializer_list<std::pair<nostd::string_view, common::AttributeValue>>
+               attributes) noexcept
+  {
+    this->Add(value, nostd::span<const std::pair<nostd::string_view, common::AttributeValue>>{
+                         attributes.begin(), attributes.end()});
+  }
 };
 
 /** A histogram instrument that records values. */
@@ -48,7 +66,7 @@ class Historgram : public SynchronousInstrument
    *
    * @param value The increment amount. May be positive, negative or zero.
    */
-  virtual void record(T value) noexcept = 0;
+  virtual void Record(T value) noexcept = 0;
 
   /**
    * Records a value with a set of attributes.
@@ -56,7 +74,22 @@ class Historgram : public SynchronousInstrument
    * @param value The increment amount. May be positive, negative or zero.
    * @param attributes A set of attributes to associate with the count.
    */
-  void record(T value, const common::KeyValueIterable &attributes) noexcept = 0;
+  virtual void Record(T value, const common::KeyValueIterable &attributes) noexcept = 0;
+
+  template <class U,
+            nostd::enable_if_t<common::detail::is_key_value_iterable<U>::value> * = nullptr>
+  void Record(T value, const U &attributes) noexcept
+  {
+    this->Record(value, common::KeyValueIterableView<T>{attributes});
+  }
+
+  void Record(T value,
+              std::initializer_list<std::pair<nostd::string_view, common::AttributeValue>>
+                  attributes) noexcept
+  {
+    this->Record(value, nostd::span<const std::pair<nostd::string_view, common::AttributeValue>>{
+                            attributes.begin(), attributes.end()});
+  }
 
 }
 
@@ -71,7 +104,7 @@ class UpDownCounter : public SynchronousInstrument
    *
    * @param value The amount of the measurement.
    */
-  virtual void add(T value) noexcept = 0;
+  virtual void Add(T value) noexcept = 0;
 
   /**
    * Add a value with a set of attributes.
@@ -79,7 +112,22 @@ class UpDownCounter : public SynchronousInstrument
    * @param value The increment amount. May be positive, negative or zero.
    * @param attributes A set of attributes to associate with the count.
    */
-  void add(T value, const common::KeyValueIterable &attributes) noexcept = 0;
+  void Add(T value, const common::KeyValueIterable &attributes) noexcept = 0;
+
+  template <class U,
+            nostd::enable_if_t<common::detail::is_key_value_iterable<U>::value> * = nullptr>
+  void Add(T value, const U &attributes) noexcept
+  {
+    this->Add(value, common::KeyValueIterableView<T>{attributes});
+  }
+
+  void Add(T value,
+           std::initializer_list<std::pair<nostd::string_view, common::AttributeValue>>
+               attributes) noexcept
+  {
+    this->Add(value, nostd::span<const std::pair<nostd::string_view, common::AttributeValue>>{
+                         attributes.begin(), attributes.end()});
+  }
 };
 
 }  // namespace metrics_new

From 49ff6e2575995e519bd6d10d9f5251b7f1e9d302 Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Mon, 25 Oct 2021 15:47:25 -0700
Subject: [PATCH 06/14] format

---
 CMakeLists.txt | 1 -
 1 file changed, 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5a72275bdc..b6e2585631 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -433,4 +433,3 @@ install(
   EXPORT "${PROJECT_NAME}-target"
   NAMESPACE "${PROJECT_NAME}::"
   DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}")
-  
\ No newline at end of file

From 0fd654b89134c5f8cabe22a3c808d370bac13674 Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Tue, 26 Oct 2021 15:03:57 -0700
Subject: [PATCH 07/14] add noop

---
 api/include/opentelemetry/metrics_new/meter.h | 146 ++++--------------
 api/include/opentelemetry/metrics_new/noop.h  |  90 +++++++++++
 2 files changed, 116 insertions(+), 120 deletions(-)
 create mode 100644 api/include/opentelemetry/metrics_new/noop.h

diff --git a/api/include/opentelemetry/metrics_new/meter.h b/api/include/opentelemetry/metrics_new/meter.h
index 65b5f065db..4844041a35 100644
--- a/api/include/opentelemetry/metrics_new/meter.h
+++ b/api/include/opentelemetry/metrics_new/meter.h
@@ -33,31 +33,18 @@ class Meter
    * @param name the name of the new Counter.
    * @param description a brief description of what the Counter is used for.
    * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
-   * @param enabled a boolean value that turns on or off the metric instrument.
    * @return a shared pointer to the created Counter.
    */
-  virtual nostd::shared_ptr<Counter<short>> CreateShortCounter(
-      nostd::string_view name,
-      nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true) noexcept = 0;
-
-  virtual nostd::shared_ptr<Counter<int>> CreateIntCounter(nostd::string_view name,
-                                                           nostd::string_view description = "",
-                                                           nostd::string_view unit        = "",
-                                                           const bool enabled = true) noexcept = 0;
 
-  virtual nostd::shared_ptr<Counter<float>> CreateFloatCounter(
+  virtual nostd::shared_ptr<Counter<long>> CreateLongCounter(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true) noexcept = 0;
+      nostd::string_view unit        = "") noexcept = 0;
 
   virtual nostd::shared_ptr<Counter<double>> CreateDoubleCounter(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true) noexcept = 0;
+      nostd::string_view unit        = "") noexcept = 0;
 
   /**
    * Creates a Asynchronouse (Observable) counter with the passed characteristics and returns a
@@ -66,37 +53,20 @@ class Meter
    * @param name the name of the new Observable Counter.
    * @param description a brief description of what the Observable Counter is used for.
    * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
-   * @param enabled a boolean value that turns on or off the metric instrument.
    * @param callback the function to be observed by the instrument.
    * @return a shared pointer to the created Observable Counter.
    */
-  virtual nostd::shared_ptr<ObservableCounter<short>> CreateShortObservableCounter(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<short>),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true) noexcept = 0;
-
-  virtual nostd::shared_ptr<ObservableCounter<int>> CreateIntObservableCounter(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<int>),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true, ) noexcept = 0;
-
-  virtual nostd::shared_ptr<ObservableCounter<float>> CreateFloatObservableCounter(
+  virtual nostd::shared_ptr<ObservableCounter<long>> CreateLongObservableCounter(
       nostd::string_view name,
+      void (*callback)(ObserverResult<long>),
       nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true,
-      void (*callback)(ObserverResult<float>)) noexcept = 0;
+      nostd::string_view unit        = "") noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableCounter<double>> CreateDoubleObservableCounter(
       nostd::string_view name,
+      void (*callback)(ObserverResult<double>),
       nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true,
-      void (*callback)(ObserverResult<double>)) noexcept = 0;
+      nostd::string_view unit        = "") noexcept = 0;
 
   /**
    * Creates a Histogram with the passed characteristics and returns a shared_ptr to that Histogram.
@@ -104,32 +74,17 @@ class Meter
    * @param name the name of the new Histogram.
    * @param description a brief description of what the Histogram is used for.
    * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
-   * @param enabled a boolean value that turns on or off the metric instrument.
    * @return a shared pointer to the created Histogram.
    */
-  virtual nostd::shared_ptr<Histogram<short>> CreateShortHistogram(
+  virtual nostd::shared_ptr<Histogram<long>> CreateLongHistogram(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true) noexcept = 0;
-
-  virtual nostd::shared_ptr<Histogram<int>> CreateIntHistogram(
-      nostd::string_view name,
-      nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true) noexcept = 0;
-
-  virtual nostd::shared_ptr<Histogram<float>> CreateFloatHistogram(
-      nostd::string_view name,
-      nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true) noexcept = 0;
+      nostd::string_view unit        = "") noexcept = 0;
 
   virtual nostd::shared_ptr<Histogram<double>> CreateDoubleHistogram(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true) noexcept = 0;
+      nostd::string_view unit        = "") noexcept = 0;
 
   /**
    * Creates a Asynchronouse (Observable) Gauge with the passed characteristics and returns a
@@ -138,37 +93,20 @@ class Meter
    * @param name the name of the new Observable Gauge.
    * @param description a brief description of what the Observable Gauge is used for.
    * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
-   * @param enabled a boolean value that turns on or off the metric instrument.
    * @param callback the function to be observed by the instrument.
    * @return a shared pointer to the created Observable Gauge.
    */
-  virtual nostd::shared_ptr<ObservableGauge<short>> CreateShortObservableGauge(
+  virtual nostd::shared_ptr<ObservableGauge<long>> CreateLongObservableGauge(
       nostd::string_view name,
-      void (*callback)(ObserverResult<short>),
+      void (*callback)(ObserverResult<long>),
       nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true) noexcept = 0;
-
-  virtual nostd::shared_ptr<ObservableGauge<int>> CreateIntObservableGauge(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<int>),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true, ) noexcept = 0;
-
-  virtual nostd::shared_ptr<ObservableGauge<float>> CreateFloatObservableGauge(
-      nostd::string_view name,
-      nostd::string_view description,
-      nostd::string_view unit,
-      const bool enabled,
-      void (*callback)(ObserverResult<float>)) noexcept = 0;
+      nostd::string_view unit        = "") noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableGauge<double>> CreateDoubleObservableGauge(
       nostd::string_view name,
-      nostd::string_view description,
-      nostd::string_view unit,
-      const bool enabled,
-      void (*callback)(ObserverResult<double>)) noexcept = 0;
+      void (*callback)(ObserverResult<double>),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept = 0;
 
   /**
    * Creates an UpDownCounter with the passed characteristics and returns a shared_ptr to that
@@ -177,32 +115,17 @@ class Meter
    * @param name the name of the new UpDownCounter.
    * @param description a brief description of what the UpDownCounter is used for.
    * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
-   * @param enabled a boolean value that turns on or off the metric instrument.
    * @return a shared pointer to the created UpDownCounter.
    */
-  virtual nostd::shared_ptr<UpDownCounter<short>> CreateShortUpDownCounter(
-      nostd::string_view name,
-      nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true) noexcept = 0;
-
-  virtual nostd::shared_ptr<UpDownCounter<int>> CreateIntUpDownCounter(
-      nostd::string_view name,
-      nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true) = 0;
-
-  virtual nostd::shared_ptr<UpDownCounter<float>> CreateFloatUpDownCounter(
+  virtual nostd::shared_ptr<UpDownCounter<long>> CreateLongUpDownCounter(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true) noexcept = 0;
+      nostd::string_view unit        = "") noexcept = 0;
 
   virtual nostd::shared_ptr<UpDownCounter<double>> CreateDoubleUpDownCounter(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true) noexcept = 0;
+      nostd::string_view unit        = "") noexcept = 0;
 
   /**
    * Creates a Asynchronouse (Observable) UpDownCounter with the passed characteristics and returns
@@ -211,37 +134,20 @@ class Meter
    * @param name the name of the new Observable UpDownCounter.
    * @param description a brief description of what the Observable UpDownCounter is used for.
    * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
-   * @param enabled a boolean value that turns on or off the metric instrument.
    * @param callback the function to be observed by the instrument.
    * @return a shared pointer to the created Observable UpDownCounter.
    */
-  virtual nostd::shared_ptr<ObservableUpDownCounter<short>> CreateShortObservableUpDownCounter(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<short>),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true) noexcept = 0;
-
-  virtual nostd::shared_ptr<ObservableUpDownCounter<int>> CreateIntObservableUpDownCounter(
+  virtual nostd::shared_ptr<ObservableUpDownCounter<long>> CreateLongObservableUpDownCounter(
       nostd::string_view name,
-      void (*callback)(ObserverResult<int>),
+      void (*callback)(ObserverResult<long>),
       nostd::string_view description = "",
-      nostd::string_view unit        = "",
-      const bool enabled             = true, ) noexcept = 0;
-
-  virtual nostd::shared_ptr<ObservableUpDownCounter<float>> CreateFloatObservableUpDownCounter(
-      nostd::string_view name,
-      nostd::string_view description,
-      nostd::string_view unit,
-      const bool enabled,
-      void (*callback)(ObserverResult<float>)) noexcept = 0;
+      nostd::string_view unit        = "") noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableUpDownCounter<double>> CreateDoubleObservableUpDownCounter(
       nostd::string_view name,
-      nostd::string_view description,
-      nostd::string_view unit,
-      const bool enabled,
-      void (*callback)(ObserverResult<double>)) noexcept = 0;
+      void (*callback)(ObserverResult<double>),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept = 0;
 };
 }  // namespace metrics_new
 OPENTELEMETRY_END_NAMESPACE
diff --git a/api/include/opentelemetry/metrics_new/noop.h b/api/include/opentelemetry/metrics_new/noop.h
new file mode 100644
index 0000000000..f984907612
--- /dev/null
+++ b/api/include/opentelemetry/metrics_new/noop.h
@@ -0,0 +1,90 @@
+#include "opentelemetry/metrics_new/sync_instruments.h"
+
+OPENTELEMETRY_BEGIN_NAMESPACE
+namespace metrics_new
+{
+
+template <class T>
+class NoopCounter : public opentelemetry::metrics_new::Counter
+{
+public:
+  void Add(T value) noexcept override {}
+  void Add(T value, const common::KeyValueIterable &attributes) {}
+}
+
+template <class T>
+class NoopHistorgram : public opentelemetry::metrics_new::Historgram
+{
+public:
+  void Add(T value) noexcept override {}
+  void Add(T value, const common::KeyValueIterable &attributes) {}
+}
+
+template <class T>
+class NoopUpDownCounter : public opentelemetry::metrics_new::UpDownCounter
+{
+public:
+  void Add(T value) noexcept override {}
+  void Add(T value, const common::KeyValueIterable &attributes) {}
+}
+
+template <class T>
+class NoopObservableCounter : public ObservableCounter
+{};
+
+template <class T>
+class NoopObservableGauge : public ObservableGauge
+{};
+
+template <class T>
+class NoopObservableUpDownCounter : public ObservableUpDownCounter
+{};
+
+/**
+ * No-op implementation of Meter.
+ */
+class NoopMeter final : public opentelemetry::Meter
+{
+public:
+  // Tracer
+  nostd::shared_ptr<Span> StartSpan(nostd::string_view /*name*/,
+                                    const common::KeyValueIterable & /*attributes*/,
+                                    const SpanContextKeyValueIterable & /*links*/,
+                                    const StartSpanOptions & /*options*/) noexcept override
+  {
+    // Don't allocate a no-op span for every StartSpan call, but use a static
+    // singleton for this case.
+    static nostd::shared_ptr<trace_api::Span> noop_span(
+        new trace_api::NoopSpan{this->shared_from_this()});
+
+    return noop_span;
+  }
+
+  void ForceFlushWithMicroseconds(uint64_t /*timeout*/) noexcept override {}
+
+  void CloseWithMicroseconds(uint64_t /*timeout*/) noexcept override {}
+};
+
+/**
+ * No-op implementation of a TracerProvider.
+ */
+class NoopMeterProvider final : public opentelemetry::trace::MeterProvider
+{
+public:
+  NoopMeterProvider()
+      : tracer_{
+            nostd::shared_ptr<opentelemetry::trace::NoopMeter>(new opentelemetry::trace::NoopMeter)}
+  {}
+
+  nostd::shared_ptr<opentelemetry::trace::Tracer> GetMeter(nostd::string_view library_name,
+                                                           nostd::string_view library_version,
+                                                           nostd::string_view schema_url) override
+  {
+    return meter_;
+  }
+
+private:
+  nostd::shared_ptr<opentelemetry::trace::Tracer> meter_;
+};
+}  // namespace metrics_new
+OPENTELEMETRY_END_NAMESPACE
\ No newline at end of file

From ff80cbe27e4e8065e9992a849ed8514be6da793c Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Wed, 27 Oct 2021 23:54:10 -0700
Subject: [PATCH 08/14] add unit tests

---
 .../metrics_new/async_instruments.h           |   2 -
 api/include/opentelemetry/metrics_new/meter.h |   1 -
 .../metrics_new/meter_provider.h              |   5 +-
 api/include/opentelemetry/metrics_new/noop.h  | 208 ++++++++++++++----
 .../metrics_new/observer_result.h             |   1 +
 .../opentelemetry/metrics_new/provider.h      |   4 +-
 .../metrics_new/sync_instruments.h            |  13 +-
 api/test/CMakeLists.txt                       |   2 +
 api/test/metrics_new/CMakeLists.txt           |   9 +
 api/test/metrics_new/meter_provider_test.cc   |  35 +++
 .../metrics_new/noop_sync_instrument_test.cc  |  39 ++++
 11 files changed, 266 insertions(+), 53 deletions(-)
 create mode 100644 api/test/metrics_new/CMakeLists.txt
 create mode 100644 api/test/metrics_new/meter_provider_test.cc
 create mode 100644 api/test/metrics_new/noop_sync_instrument_test.cc

diff --git a/api/include/opentelemetry/metrics_new/async_instruments.h b/api/include/opentelemetry/metrics_new/async_instruments.h
index 143206789e..1bd095f50c 100644
--- a/api/include/opentelemetry/metrics_new/async_instruments.h
+++ b/api/include/opentelemetry/metrics_new/async_instruments.h
@@ -3,7 +3,6 @@
 
 #pragma once
 
-#include "instrument.h"
 #include "observer_result.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
@@ -26,4 +25,3 @@ class ObservableUpDownCounter : public AsynchronousInstrument
 
 }  // namespace metrics_new
 OPENTELEMETRY_END_NAMESPACE
-#endif
diff --git a/api/include/opentelemetry/metrics_new/meter.h b/api/include/opentelemetry/metrics_new/meter.h
index 4844041a35..0a5a1611ed 100644
--- a/api/include/opentelemetry/metrics_new/meter.h
+++ b/api/include/opentelemetry/metrics_new/meter.h
@@ -4,7 +4,6 @@
 #pragma once
 
 #include "opentelemetry/metrics_new/async_instruments.h"
-#include "opentelemetry/metrics_new/instrument.h"
 #include "opentelemetry/metrics_new/sync_instruments.h"
 #include "opentelemetry/nostd/shared_ptr.h"
 #include "opentelemetry/nostd/span.h"
diff --git a/api/include/opentelemetry/metrics_new/meter_provider.h b/api/include/opentelemetry/metrics_new/meter_provider.h
index e5579694ce..a010d551f6 100644
--- a/api/include/opentelemetry/metrics_new/meter_provider.h
+++ b/api/include/opentelemetry/metrics_new/meter_provider.h
@@ -3,7 +3,7 @@
 
 #pragma once
 
-#include "opentelemetry/metrics/meter.h"
+#include "opentelemetry/metrics_new/meter.h"
 #include "opentelemetry/nostd/shared_ptr.h"
 #include "opentelemetry/nostd/string_view.h"
 
@@ -26,5 +26,6 @@ class MeterProvider
   virtual nostd::shared_ptr<Meter> GetMeter(nostd::string_view library_name,
                                             nostd::string_view library_version = "",
                                             nostd::string_view schema_url      = "") noexcept = 0;
-}  // namespace metrics
+};
+}  // namespace metrics_new
 OPENTELEMETRY_END_NAMESPACE
diff --git a/api/include/opentelemetry/metrics_new/noop.h b/api/include/opentelemetry/metrics_new/noop.h
index f984907612..7738f488e9 100644
--- a/api/include/opentelemetry/metrics_new/noop.h
+++ b/api/include/opentelemetry/metrics_new/noop.h
@@ -1,90 +1,220 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#pragma once
+#include "opentelemetry/metrics_new/async_instruments.h"
+#include "opentelemetry/metrics_new/meter.h"
+#include "opentelemetry/metrics_new/meter_provider.h"
+#include "opentelemetry/metrics_new/observer_result.h"
 #include "opentelemetry/metrics_new/sync_instruments.h"
+#include "opentelemetry/version.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
 namespace metrics_new
 {
 
 template <class T>
-class NoopCounter : public opentelemetry::metrics_new::Counter
+class NoopCounter : public Counter<T>
 {
 public:
+  NoopCounter(nostd::string_view name,
+              nostd::string_view description,
+              nostd::string_view unit) noexcept
+  {}
   void Add(T value) noexcept override {}
-  void Add(T value, const common::KeyValueIterable &attributes) {}
-}
+  void Add(T value, const common::KeyValueIterable &attributes) noexcept override {}
+};
 
 template <class T>
-class NoopHistorgram : public opentelemetry::metrics_new::Historgram
+class NoopHistogram : public Histogram<T>
 {
 public:
-  void Add(T value) noexcept override {}
-  void Add(T value, const common::KeyValueIterable &attributes) {}
-}
+  NoopHistogram(nostd::string_view name,
+                nostd::string_view description,
+                nostd::string_view unit) noexcept
+  {}
+  void Record(T value) noexcept override {}
+  void Record(T value, const common::KeyValueIterable &attributes) noexcept override {}
+};
 
 template <class T>
-class NoopUpDownCounter : public opentelemetry::metrics_new::UpDownCounter
+class NoopUpDownCounter : public UpDownCounter<T>
 {
 public:
+  NoopUpDownCounter(nostd::string_view name,
+                    nostd::string_view description,
+                    nostd::string_view unit) noexcept
+  {}
   void Add(T value) noexcept override {}
-  void Add(T value, const common::KeyValueIterable &attributes) {}
-}
+  void Add(T value, const common::KeyValueIterable &attributes) noexcept override {}
+};
 
 template <class T>
-class NoopObservableCounter : public ObservableCounter
-{};
+class NoopObservableCounter : public ObservableCounter<T>
+{
+public:
+  NoopObservableCounter(nostd::string_view name,
+                        void (*callback)(ObserverResult<T>),
+                        nostd::string_view description,
+                        nostd::string_view unit) noexcept
+  {}
+};
 
 template <class T>
-class NoopObservableGauge : public ObservableGauge
-{};
+class NoopObservableGauge : public ObservableGauge<T>
+{
+public:
+  NoopObservableGauge(nostd::string_view name,
+                      void (*callback)(ObserverResult<T>),
+                      nostd::string_view description,
+                      nostd::string_view unit) noexcept
+  {}
+};
 
 template <class T>
-class NoopObservableUpDownCounter : public ObservableUpDownCounter
-{};
+class NoopObservableUpDownCounter : public ObservableUpDownCounter<T>
+{
+public:
+  NoopObservableUpDownCounter(nostd::string_view name,
+                              void (*callback)(ObserverResult<T>),
+                              nostd::string_view description,
+                              nostd::string_view unit) noexcept
+  {}
+};
 
 /**
  * No-op implementation of Meter.
  */
-class NoopMeter final : public opentelemetry::Meter
+class NoopMeter final : public Meter
 {
 public:
-  // Tracer
-  nostd::shared_ptr<Span> StartSpan(nostd::string_view /*name*/,
-                                    const common::KeyValueIterable & /*attributes*/,
-                                    const SpanContextKeyValueIterable & /*links*/,
-                                    const StartSpanOptions & /*options*/) noexcept override
+  nostd::shared_ptr<Counter<long>> CreateLongCounter(nostd::string_view name,
+                                                     nostd::string_view description = "",
+                                                     nostd::string_view unit = "") noexcept override
   {
-    // Don't allocate a no-op span for every StartSpan call, but use a static
-    // singleton for this case.
-    static nostd::shared_ptr<trace_api::Span> noop_span(
-        new trace_api::NoopSpan{this->shared_from_this()});
+    return nostd::shared_ptr<Counter<long>>{new NoopCounter<long>(name, description, unit)};
+  }
 
-    return noop_span;
+  nostd::shared_ptr<Counter<double>> CreateDoubleCounter(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<Counter<double>>{new NoopCounter<double>(name, description, unit)};
   }
 
-  void ForceFlushWithMicroseconds(uint64_t /*timeout*/) noexcept override {}
+  nostd::shared_ptr<ObservableCounter<long>> CreateLongObservableCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<long>),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<ObservableCounter<long>>{
+        new NoopObservableCounter<long>(name, callback, description, unit)};
+  }
 
-  void CloseWithMicroseconds(uint64_t /*timeout*/) noexcept override {}
+  nostd::shared_ptr<ObservableCounter<double>> CreateDoubleObservableCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<double>),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<ObservableCounter<double>>{
+        new NoopObservableCounter<double>(name, callback, description, unit)};
+  }
+
+  nostd::shared_ptr<Histogram<long>> CreateLongHistogram(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<Histogram<long>>{new NoopHistogram<long>(name, description, unit)};
+  }
+
+  nostd::shared_ptr<Histogram<double>> CreateDoubleHistogram(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<Histogram<double>>{new NoopHistogram<double>(name, description, unit)};
+  }
+
+  nostd::shared_ptr<ObservableGauge<long>> CreateLongObservableGauge(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<long>),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<ObservableGauge<long>>{
+        new NoopObservableGauge<long>(name, callback, description, unit)};
+  }
+
+  nostd::shared_ptr<ObservableGauge<double>> CreateDoubleObservableGauge(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<double>),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<ObservableGauge<double>>{
+        new NoopObservableGauge<double>(name, callback, description, unit)};
+  }
+
+  nostd::shared_ptr<UpDownCounter<long>> CreateLongUpDownCounter(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<UpDownCounter<long>>{
+        new NoopUpDownCounter<long>(name, description, unit)};
+  }
+
+  nostd::shared_ptr<UpDownCounter<double>> CreateDoubleUpDownCounter(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<UpDownCounter<double>>{
+        new NoopUpDownCounter<double>(name, description, unit)};
+  }
+
+  nostd::shared_ptr<ObservableUpDownCounter<long>> CreateLongObservableUpDownCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<long>),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<ObservableUpDownCounter<long>>{
+        new NoopObservableUpDownCounter<long>(name, callback, description, unit)};
+  }
+
+  nostd::shared_ptr<ObservableUpDownCounter<double>> CreateDoubleObservableUpDownCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<double>),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<ObservableUpDownCounter<double>>{
+        new NoopObservableUpDownCounter<double>(name, callback, description, unit)};
+  }
 };
 
 /**
- * No-op implementation of a TracerProvider.
+ * No-op implementation of a MeterProvider.
  */
-class NoopMeterProvider final : public opentelemetry::trace::MeterProvider
+class NoopMeterProvider final : public MeterProvider
 {
 public:
-  NoopMeterProvider()
-      : tracer_{
-            nostd::shared_ptr<opentelemetry::trace::NoopMeter>(new opentelemetry::trace::NoopMeter)}
-  {}
+  NoopMeterProvider() : meter_{nostd::shared_ptr<Meter>(new NoopMeter)} {}
 
-  nostd::shared_ptr<opentelemetry::trace::Tracer> GetMeter(nostd::string_view library_name,
-                                                           nostd::string_view library_version,
-                                                           nostd::string_view schema_url) override
+  nostd::shared_ptr<Meter> GetMeter(nostd::string_view library_name,
+                                    nostd::string_view library_version,
+                                    nostd::string_view schema_url) noexcept override
   {
     return meter_;
   }
 
 private:
-  nostd::shared_ptr<opentelemetry::trace::Tracer> meter_;
+  nostd::shared_ptr<Meter> meter_;
 };
 }  // namespace metrics_new
 OPENTELEMETRY_END_NAMESPACE
\ No newline at end of file
diff --git a/api/include/opentelemetry/metrics_new/observer_result.h b/api/include/opentelemetry/metrics_new/observer_result.h
index 5d78fe2f58..088d4be859 100644
--- a/api/include/opentelemetry/metrics_new/observer_result.h
+++ b/api/include/opentelemetry/metrics_new/observer_result.h
@@ -6,6 +6,7 @@
 #include "opentelemetry/common/key_value_iterable_view.h"
 #include "opentelemetry/nostd/span.h"
 #include "opentelemetry/nostd/string_view.h"
+#include "opentelemetry/nostd/type_traits.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
 namespace metrics_new
diff --git a/api/include/opentelemetry/metrics_new/provider.h b/api/include/opentelemetry/metrics_new/provider.h
index aebca3fa73..d8feeaa1f3 100644
--- a/api/include/opentelemetry/metrics_new/provider.h
+++ b/api/include/opentelemetry/metrics_new/provider.h
@@ -5,8 +5,8 @@
 #include <mutex>
 
 #include "opentelemetry/common/spin_lock_mutex.h"
-#include "opentelemetry/metrics/meter_provider.h"
-#include "opentelemetry/metrics/noop.h"
+#include "opentelemetry/metrics_new/meter_provider.h"
+#include "opentelemetry/metrics_new/noop.h"
 #include "opentelemetry/nostd/shared_ptr.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
diff --git a/api/include/opentelemetry/metrics_new/sync_instruments.h b/api/include/opentelemetry/metrics_new/sync_instruments.h
index bfeab5f95e..f0fcc8ab1d 100644
--- a/api/include/opentelemetry/metrics_new/sync_instruments.h
+++ b/api/include/opentelemetry/metrics_new/sync_instruments.h
@@ -43,7 +43,7 @@ class Counter : public SynchronousInstrument
             nostd::enable_if_t<common::detail::is_key_value_iterable<U>::value> * = nullptr>
   void Add(T value, const U &attributes) noexcept
   {
-    this->Add(value, common::KeyValueIterableView<T>{attributes});
+    this->Add(value, common::KeyValueIterableView<U>{attributes});
   }
 
   void Add(T value,
@@ -58,7 +58,7 @@ class Counter : public SynchronousInstrument
 /** A histogram instrument that records values. */
 
 template <class T>
-class Historgram : public SynchronousInstrument
+class Histogram : public SynchronousInstrument
 {
 public:
   /**
@@ -80,7 +80,7 @@ class Historgram : public SynchronousInstrument
             nostd::enable_if_t<common::detail::is_key_value_iterable<U>::value> * = nullptr>
   void Record(T value, const U &attributes) noexcept
   {
-    this->Record(value, common::KeyValueIterableView<T>{attributes});
+    this->Record(value, common::KeyValueIterableView<U>{attributes});
   }
 
   void Record(T value,
@@ -90,8 +90,7 @@ class Historgram : public SynchronousInstrument
     this->Record(value, nostd::span<const std::pair<nostd::string_view, common::AttributeValue>>{
                             attributes.begin(), attributes.end()});
   }
-
-}
+};
 
 /** An up-down-counter instrument that adds or reduce values. */
 
@@ -112,13 +111,13 @@ class UpDownCounter : public SynchronousInstrument
    * @param value The increment amount. May be positive, negative or zero.
    * @param attributes A set of attributes to associate with the count.
    */
-  void Add(T value, const common::KeyValueIterable &attributes) noexcept = 0;
+  virtual void Add(T value, const common::KeyValueIterable &attributes) noexcept = 0;
 
   template <class U,
             nostd::enable_if_t<common::detail::is_key_value_iterable<U>::value> * = nullptr>
   void Add(T value, const U &attributes) noexcept
   {
-    this->Add(value, common::KeyValueIterableView<T>{attributes});
+    this->Add(value, common::KeyValueIterableView<U>{attributes});
   }
 
   void Add(T value,
diff --git a/api/test/CMakeLists.txt b/api/test/CMakeLists.txt
index 0e4c9bd0f3..2cc72d152a 100644
--- a/api/test/CMakeLists.txt
+++ b/api/test/CMakeLists.txt
@@ -5,6 +5,8 @@ add_subdirectory(nostd)
 add_subdirectory(trace)
 if(WITH_METRICS_PREVIEW)
   add_subdirectory(metrics)
+else()
+  add_subdirectory(metrics_new)
 endif()
 if(WITH_LOGS_PREVIEW)
   add_subdirectory(logs)
diff --git a/api/test/metrics_new/CMakeLists.txt b/api/test/metrics_new/CMakeLists.txt
new file mode 100644
index 0000000000..89ce81fd01
--- /dev/null
+++ b/api/test/metrics_new/CMakeLists.txt
@@ -0,0 +1,9 @@
+foreach(testname meter_provider_test noop_sync_instrument_test)
+  add_executable(${testname} "${testname}.cc")
+  target_link_libraries(${testname} ${GTEST_BOTH_LIBRARIES}
+                        ${CMAKE_THREAD_LIBS_INIT} opentelemetry_api)
+  gtest_add_tests(
+    TARGET ${testname}
+    TEST_PREFIX metrics_new.
+    TEST_LIST ${testname})
+endforeach()
diff --git a/api/test/metrics_new/meter_provider_test.cc b/api/test/metrics_new/meter_provider_test.cc
new file mode 100644
index 0000000000..0df7cda65c
--- /dev/null
+++ b/api/test/metrics_new/meter_provider_test.cc
@@ -0,0 +1,35 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#include <gtest/gtest.h>
+#include "opentelemetry/metrics_new/noop.h"
+#include "opentelemetry/metrics_new/provider.h"
+#include "opentelemetry/nostd/shared_ptr.h"
+
+using opentelemetry::metrics_new::Meter;
+using opentelemetry::metrics_new::MeterProvider;
+using opentelemetry::metrics_new::NoopMeterProvider;
+using opentelemetry::metrics_new::Provider;
+
+TEST(Provider, GetMeterProviderDefault)
+{
+  auto tf = Provider::GetMeterProvider();
+  EXPECT_NE(nullptr, tf);
+}
+
+TEST(Provider, SetMeterProvider)
+{
+  auto tf = opentelemetry::nostd::shared_ptr<MeterProvider>(new NoopMeterProvider());
+  Provider::SetMeterProvider(tf);
+  ASSERT_EQ(tf, Provider::GetMeterProvider());
+}
+
+TEST(Provider, MultipleMeterProviders)
+{
+  auto tf = opentelemetry::nostd::shared_ptr<MeterProvider>(new NoopMeterProvider());
+  Provider::SetMeterProvider(tf);
+  auto tf2 = opentelemetry::nostd::shared_ptr<MeterProvider>(new NoopMeterProvider());
+  Provider::SetMeterProvider(tf2);
+
+  ASSERT_NE(Provider::GetMeterProvider(), tf);
+}
diff --git a/api/test/metrics_new/noop_sync_instrument_test.cc b/api/test/metrics_new/noop_sync_instrument_test.cc
new file mode 100644
index 0000000000..4922d9273d
--- /dev/null
+++ b/api/test/metrics_new/noop_sync_instrument_test.cc
@@ -0,0 +1,39 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#include <gtest/gtest.h>
+#include <map>
+#include "opentelemetry/metrics_new/noop.h"
+
+TEST(Counter, Add)
+{
+  std::shared_ptr<opentelemetry::metrics_new::Counter<long>> counter{
+      new opentelemetry::metrics_new::NoopCounter<long>("test", "none", "unitless")};
+
+  std::map<std::string, std::string> labels = {{"k1", "v1"}};
+  EXPECT_NO_THROW(counter->Add(10l, labels));
+  EXPECT_NO_THROW(counter->Add(2l));
+  EXPECT_NO_THROW(counter->Add(10l, {{"k1", "1"}, {"k2", 2}}));
+}
+
+TEST(histogram, Record)
+{
+  std::shared_ptr<opentelemetry::metrics_new::Histogram<long>> counter{
+      new opentelemetry::metrics_new::NoopHistogram<long>("test", "none", "unitless")};
+
+  std::map<std::string, std::string> labels = {{"k1", "v1"}};
+  EXPECT_NO_THROW(counter->Record(10l, labels));
+  EXPECT_NO_THROW(counter->Record(2l));
+  EXPECT_NO_THROW(counter->Record(10l, {{"k1", "1"}, {"k2", 2}}));
+}
+
+TEST(UpDownCountr, Record)
+{
+  std::shared_ptr<opentelemetry::metrics_new::UpDownCounter<long>> counter{
+      new opentelemetry::metrics_new::NoopUpDownCounter<long>("test", "none", "unitless")};
+
+  std::map<std::string, std::string> labels = {{"k1", "v1"}};
+  EXPECT_NO_THROW(counter->Add(10l, labels));
+  EXPECT_NO_THROW(counter->Add(2l));
+  EXPECT_NO_THROW(counter->Add(10l, {{"k1", "1"}, {"k2", 2}}));
+}
\ No newline at end of file

From 67961a4e79073c5fc5308eaf97c4ae2a99764fed Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Thu, 28 Oct 2021 13:40:28 -0700
Subject: [PATCH 09/14] add callback state

---
 api/include/opentelemetry/metrics_new/meter.h | 57 +++++++++--
 api/include/opentelemetry/metrics_new/noop.h  | 97 +++++++++++++++++--
 2 files changed, 136 insertions(+), 18 deletions(-)

diff --git a/api/include/opentelemetry/metrics_new/meter.h b/api/include/opentelemetry/metrics_new/meter.h
index 0a5a1611ed..368784adca 100644
--- a/api/include/opentelemetry/metrics_new/meter.h
+++ b/api/include/opentelemetry/metrics_new/meter.h
@@ -52,18 +52,31 @@ class Meter
    * @param name the name of the new Observable Counter.
    * @param description a brief description of what the Observable Counter is used for.
    * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
-   * @param callback the function to be observed by the instrument.
+   * @param callback the function to be observed by the instrument. This can optionally take `state`
+   * as key-value argument.
    * @return a shared pointer to the created Observable Counter.
    */
   virtual nostd::shared_ptr<ObservableCounter<long>> CreateLongObservableCounter(
       nostd::string_view name,
-      void (*callback)(ObserverResult<long>),
+      void (*callback)(ObserverResult<long> &),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept = 0;
+
+  virtual nostd::shared_ptr<ObservableCounter<long>> CreateLongObservableCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<long> &, const common::KeyValueIterable &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableCounter<double>> CreateDoubleObservableCounter(
       nostd::string_view name,
-      void (*callback)(ObserverResult<double>),
+      void (*callback)(ObserverResult<double> &),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept = 0;
+
+  virtual nostd::shared_ptr<ObservableCounter<double>> CreateDoubleObservableCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<double> &, const common::KeyValueIterable &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept = 0;
 
@@ -92,18 +105,31 @@ class Meter
    * @param name the name of the new Observable Gauge.
    * @param description a brief description of what the Observable Gauge is used for.
    * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
-   * @param callback the function to be observed by the instrument.
+   * @param callback the function to be observed by the instrument. This can optionally take `state`
+   * as key-value argument.
    * @return a shared pointer to the created Observable Gauge.
    */
   virtual nostd::shared_ptr<ObservableGauge<long>> CreateLongObservableGauge(
       nostd::string_view name,
-      void (*callback)(ObserverResult<long>),
+      void (*callback)(ObserverResult<long> &),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept = 0;
+
+  virtual nostd::shared_ptr<ObservableGauge<long>> CreateLongObservableGauge(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<long> &, const common::KeyValueIterable &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableGauge<double>> CreateDoubleObservableGauge(
       nostd::string_view name,
-      void (*callback)(ObserverResult<double>),
+      void (*callback)(ObserverResult<double> &),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept = 0;
+
+  virtual nostd::shared_ptr<ObservableGauge<double>> CreateDoubleObservableGauge(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<double> &, const common::KeyValueIterable &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept = 0;
 
@@ -133,18 +159,31 @@ class Meter
    * @param name the name of the new Observable UpDownCounter.
    * @param description a brief description of what the Observable UpDownCounter is used for.
    * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
-   * @param callback the function to be observed by the instrument.
+   * @param callback the function to be observed by the instrument. This can optionally take `state`
+   * as key-value argument.
    * @return a shared pointer to the created Observable UpDownCounter.
    */
   virtual nostd::shared_ptr<ObservableUpDownCounter<long>> CreateLongObservableUpDownCounter(
       nostd::string_view name,
-      void (*callback)(ObserverResult<long>),
+      void (*callback)(ObserverResult<long> &),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept = 0;
+
+  virtual nostd::shared_ptr<ObservableUpDownCounter<long>> CreateLongObservableUpDownCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<long> &, const common::KeyValueIterable &),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept = 0;
+
+  virtual nostd::shared_ptr<ObservableUpDownCounter<double>> CreateDoubleObservableUpDownCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<double> &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableUpDownCounter<double>> CreateDoubleObservableUpDownCounter(
       nostd::string_view name,
-      void (*callback)(ObserverResult<double>),
+      void (*callback)(ObserverResult<double> &, const common::KeyValueIterable &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept = 0;
 };
diff --git a/api/include/opentelemetry/metrics_new/noop.h b/api/include/opentelemetry/metrics_new/noop.h
index 7738f488e9..40623c7ba9 100644
--- a/api/include/opentelemetry/metrics_new/noop.h
+++ b/api/include/opentelemetry/metrics_new/noop.h
@@ -54,7 +54,13 @@ class NoopObservableCounter : public ObservableCounter<T>
 {
 public:
   NoopObservableCounter(nostd::string_view name,
-                        void (*callback)(ObserverResult<T>),
+                        void (*callback)(ObserverResult<T> &),
+                        nostd::string_view description,
+                        nostd::string_view unit) noexcept
+  {}
+
+  NoopObservableCounter(nostd::string_view name,
+                        void (*callback)(ObserverResult<T> &, const common::KeyValueIterable &),
                         nostd::string_view description,
                         nostd::string_view unit) noexcept
   {}
@@ -65,7 +71,13 @@ class NoopObservableGauge : public ObservableGauge<T>
 {
 public:
   NoopObservableGauge(nostd::string_view name,
-                      void (*callback)(ObserverResult<T>),
+                      void (*callback)(ObserverResult<T> &),
+                      nostd::string_view description,
+                      nostd::string_view unit) noexcept
+  {}
+
+  NoopObservableGauge(nostd::string_view name,
+                      void (*callback)(ObserverResult<T> &, const common::KeyValueIterable &),
                       nostd::string_view description,
                       nostd::string_view unit) noexcept
   {}
@@ -76,7 +88,14 @@ class NoopObservableUpDownCounter : public ObservableUpDownCounter<T>
 {
 public:
   NoopObservableUpDownCounter(nostd::string_view name,
-                              void (*callback)(ObserverResult<T>),
+                              void (*callback)(ObserverResult<T> &),
+                              nostd::string_view description,
+                              nostd::string_view unit) noexcept
+  {}
+
+  NoopObservableUpDownCounter(nostd::string_view name,
+                              void (*callback)(ObserverResult<T> &,
+                                               const common::KeyValueIterable &),
                               nostd::string_view description,
                               nostd::string_view unit) noexcept
   {}
@@ -105,7 +124,17 @@ class NoopMeter final : public Meter
 
   nostd::shared_ptr<ObservableCounter<long>> CreateLongObservableCounter(
       nostd::string_view name,
-      void (*callback)(ObserverResult<long>),
+      void (*callback)(ObserverResult<long> &),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<ObservableCounter<long>>{
+        new NoopObservableCounter<long>(name, callback, description, unit)};
+  }
+
+  nostd::shared_ptr<ObservableCounter<long>> CreateLongObservableCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<long> &, const common::KeyValueIterable &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept override
   {
@@ -115,7 +144,17 @@ class NoopMeter final : public Meter
 
   nostd::shared_ptr<ObservableCounter<double>> CreateDoubleObservableCounter(
       nostd::string_view name,
-      void (*callback)(ObserverResult<double>),
+      void (*callback)(ObserverResult<double> &),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<ObservableCounter<double>>{
+        new NoopObservableCounter<double>(name, callback, description, unit)};
+  }
+
+  nostd::shared_ptr<ObservableCounter<double>> CreateDoubleObservableCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<double> &, const common::KeyValueIterable &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept override
   {
@@ -141,7 +180,17 @@ class NoopMeter final : public Meter
 
   nostd::shared_ptr<ObservableGauge<long>> CreateLongObservableGauge(
       nostd::string_view name,
-      void (*callback)(ObserverResult<long>),
+      void (*callback)(ObserverResult<long> &),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<ObservableGauge<long>>{
+        new NoopObservableGauge<long>(name, callback, description, unit)};
+  }
+
+  nostd::shared_ptr<ObservableGauge<long>> CreateLongObservableGauge(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<long> &, const common::KeyValueIterable &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept override
   {
@@ -151,7 +200,17 @@ class NoopMeter final : public Meter
 
   nostd::shared_ptr<ObservableGauge<double>> CreateDoubleObservableGauge(
       nostd::string_view name,
-      void (*callback)(ObserverResult<double>),
+      void (*callback)(ObserverResult<double> &),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<ObservableGauge<double>>{
+        new NoopObservableGauge<double>(name, callback, description, unit)};
+  }
+
+  nostd::shared_ptr<ObservableGauge<double>> CreateDoubleObservableGauge(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<double> &, const common::KeyValueIterable &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept override
   {
@@ -179,7 +238,17 @@ class NoopMeter final : public Meter
 
   nostd::shared_ptr<ObservableUpDownCounter<long>> CreateLongObservableUpDownCounter(
       nostd::string_view name,
-      void (*callback)(ObserverResult<long>),
+      void (*callback)(ObserverResult<long> &),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<ObservableUpDownCounter<long>>{
+        new NoopObservableUpDownCounter<long>(name, callback, description, unit)};
+  }
+
+  nostd::shared_ptr<ObservableUpDownCounter<long>> CreateLongObservableUpDownCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<long> &, const common::KeyValueIterable &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept override
   {
@@ -189,7 +258,17 @@ class NoopMeter final : public Meter
 
   nostd::shared_ptr<ObservableUpDownCounter<double>> CreateDoubleObservableUpDownCounter(
       nostd::string_view name,
-      void (*callback)(ObserverResult<double>),
+      void (*callback)(ObserverResult<double> &),
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::shared_ptr<ObservableUpDownCounter<double>>{
+        new NoopObservableUpDownCounter<double>(name, callback, description, unit)};
+  }
+
+  nostd::shared_ptr<ObservableUpDownCounter<double>> CreateDoubleObservableUpDownCounter(
+      nostd::string_view name,
+      void (*callback)(ObserverResult<double> &, const common::KeyValueIterable &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept override
   {

From b745284e84f02eff45f6186e63fd142fdd3112ee Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Tue, 9 Nov 2021 20:06:00 -0800
Subject: [PATCH 10/14] rename metrics_new to metrics

---
 .../async_instruments.h                       |  8 ++++---
 .../{metrics_new => metrics}/meter.h          | 18 +++++++-------
 .../{metrics_new => metrics}/meter_provider.h | 12 ++++++----
 .../{metrics_new => metrics}/noop.h           | 21 +++++++++-------
 .../observer_result.h                         | 17 +++++++------
 .../{metrics_new => metrics}/provider.h       | 19 ++++++++-------
 .../sync_instruments.h                        |  4 ++--
 .../{metrics_new => metrics}/CMakeLists.txt   |  0
 .../meter_provider_test.cc                    | 19 ++++++++-------
 .../noop_sync_instrument_test.cc              | 24 +++++++++++--------
 10 files changed, 82 insertions(+), 60 deletions(-)
 rename api/include/opentelemetry/{metrics_new => metrics}/async_instruments.h (79%)
 rename api/include/opentelemetry/{metrics_new => metrics}/meter.h (95%)
 rename api/include/opentelemetry/{metrics_new => metrics}/meter_provider.h (75%)
 rename api/include/opentelemetry/{metrics_new => metrics}/noop.h (96%)
 rename api/include/opentelemetry/{metrics_new => metrics}/observer_result.h (75%)
 rename api/include/opentelemetry/{metrics_new => metrics}/provider.h (77%)
 rename api/include/opentelemetry/{metrics_new => metrics}/sync_instruments.h (98%)
 rename api/test/{metrics_new => metrics}/CMakeLists.txt (100%)
 rename api/test/{metrics_new => metrics}/meter_provider_test.cc (66%)
 rename api/test/{metrics_new => metrics}/noop_sync_instrument_test.cc (60%)

diff --git a/api/include/opentelemetry/metrics_new/async_instruments.h b/api/include/opentelemetry/metrics/async_instruments.h
similarity index 79%
rename from api/include/opentelemetry/metrics_new/async_instruments.h
rename to api/include/opentelemetry/metrics/async_instruments.h
index 1bd095f50c..daf43a32f5 100644
--- a/api/include/opentelemetry/metrics_new/async_instruments.h
+++ b/api/include/opentelemetry/metrics/async_instruments.h
@@ -2,11 +2,12 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #pragma once
+#ifndef ENABLE_METRICS_PREVIEW
 
-#include "observer_result.h"
+#  include "observer_result.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
-namespace metrics_new
+namespace metrics
 {
 class AsynchronousInstrument
 {};
@@ -23,5 +24,6 @@ template <class T>
 class ObservableUpDownCounter : public AsynchronousInstrument
 {};
 
-}  // namespace metrics_new
+}  // namespace metrics
 OPENTELEMETRY_END_NAMESPACE
+#endif
diff --git a/api/include/opentelemetry/metrics_new/meter.h b/api/include/opentelemetry/metrics/meter.h
similarity index 95%
rename from api/include/opentelemetry/metrics_new/meter.h
rename to api/include/opentelemetry/metrics/meter.h
index 368784adca..a56e1c3417 100644
--- a/api/include/opentelemetry/metrics_new/meter.h
+++ b/api/include/opentelemetry/metrics/meter.h
@@ -2,16 +2,17 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #pragma once
+#ifndef ENABLE_METRICS_PREVIEW
 
-#include "opentelemetry/metrics_new/async_instruments.h"
-#include "opentelemetry/metrics_new/sync_instruments.h"
-#include "opentelemetry/nostd/shared_ptr.h"
-#include "opentelemetry/nostd/span.h"
-#include "opentelemetry/nostd/string_view.h"
-#include "opentelemetry/version.h"
+#  include "opentelemetry/metrics/async_instruments.h"
+#  include "opentelemetry/metrics/sync_instruments.h"
+#  include "opentelemetry/nostd/shared_ptr.h"
+#  include "opentelemetry/nostd/span.h"
+#  include "opentelemetry/nostd/string_view.h"
+#  include "opentelemetry/version.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
-namespace metrics_new
+namespace metrics
 {
 /**
  * Handles instrument creation and provides a facility for batch recording.
@@ -187,5 +188,6 @@ class Meter
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept = 0;
 };
-}  // namespace metrics_new
+}  // namespace metrics
 OPENTELEMETRY_END_NAMESPACE
+#endif
diff --git a/api/include/opentelemetry/metrics_new/meter_provider.h b/api/include/opentelemetry/metrics/meter_provider.h
similarity index 75%
rename from api/include/opentelemetry/metrics_new/meter_provider.h
rename to api/include/opentelemetry/metrics/meter_provider.h
index a010d551f6..1892c7d8f9 100644
--- a/api/include/opentelemetry/metrics_new/meter_provider.h
+++ b/api/include/opentelemetry/metrics/meter_provider.h
@@ -2,13 +2,14 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #pragma once
+#ifndef ENABLE_METRICS_PREVIEW
 
-#include "opentelemetry/metrics_new/meter.h"
-#include "opentelemetry/nostd/shared_ptr.h"
-#include "opentelemetry/nostd/string_view.h"
+#  include "opentelemetry/metrics/meter.h"
+#  include "opentelemetry/nostd/shared_ptr.h"
+#  include "opentelemetry/nostd/string_view.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
-namespace metrics_new
+namespace metrics
 {
 /**
  * Creates new Meter instances.
@@ -27,5 +28,6 @@ class MeterProvider
                                             nostd::string_view library_version = "",
                                             nostd::string_view schema_url      = "") noexcept = 0;
 };
-}  // namespace metrics_new
+}  // namespace metrics
 OPENTELEMETRY_END_NAMESPACE
+#endif
diff --git a/api/include/opentelemetry/metrics_new/noop.h b/api/include/opentelemetry/metrics/noop.h
similarity index 96%
rename from api/include/opentelemetry/metrics_new/noop.h
rename to api/include/opentelemetry/metrics/noop.h
index 40623c7ba9..f596c94f39 100644
--- a/api/include/opentelemetry/metrics_new/noop.h
+++ b/api/include/opentelemetry/metrics/noop.h
@@ -2,15 +2,17 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #pragma once
-#include "opentelemetry/metrics_new/async_instruments.h"
-#include "opentelemetry/metrics_new/meter.h"
-#include "opentelemetry/metrics_new/meter_provider.h"
-#include "opentelemetry/metrics_new/observer_result.h"
-#include "opentelemetry/metrics_new/sync_instruments.h"
-#include "opentelemetry/version.h"
+#ifndef ENABLE_METRICS_PREVIEW
+
+#  include "opentelemetry/metrics/async_instruments.h"
+#  include "opentelemetry/metrics/meter.h"
+#  include "opentelemetry/metrics/meter_provider.h"
+#  include "opentelemetry/metrics/observer_result.h"
+#  include "opentelemetry/metrics/sync_instruments.h"
+#  include "opentelemetry/version.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
-namespace metrics_new
+namespace metrics
 {
 
 template <class T>
@@ -295,5 +297,6 @@ class NoopMeterProvider final : public MeterProvider
 private:
   nostd::shared_ptr<Meter> meter_;
 };
-}  // namespace metrics_new
-OPENTELEMETRY_END_NAMESPACE
\ No newline at end of file
+}  // namespace metrics
+OPENTELEMETRY_END_NAMESPACE
+#endif
\ No newline at end of file
diff --git a/api/include/opentelemetry/metrics_new/observer_result.h b/api/include/opentelemetry/metrics/observer_result.h
similarity index 75%
rename from api/include/opentelemetry/metrics_new/observer_result.h
rename to api/include/opentelemetry/metrics/observer_result.h
index 088d4be859..355b5a4a31 100644
--- a/api/include/opentelemetry/metrics_new/observer_result.h
+++ b/api/include/opentelemetry/metrics/observer_result.h
@@ -2,14 +2,16 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #pragma once
-#include "opentelemetry/common/attribute_value.h"
-#include "opentelemetry/common/key_value_iterable_view.h"
-#include "opentelemetry/nostd/span.h"
-#include "opentelemetry/nostd/string_view.h"
-#include "opentelemetry/nostd/type_traits.h"
+#ifndef ENABLE_METRICS_PREVIEW
+
+#  include "opentelemetry/common/attribute_value.h"
+#  include "opentelemetry/common/key_value_iterable_view.h"
+#  include "opentelemetry/nostd/span.h"
+#  include "opentelemetry/nostd/string_view.h"
+#  include "opentelemetry/nostd/type_traits.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
-namespace metrics_new
+namespace metrics
 {
 
 /**
@@ -42,5 +44,6 @@ class ObserverResult
   }
 };
 
-}  // namespace metrics_new
+}  // namespace metrics
 OPENTELEMETRY_END_NAMESPACE
+#endif
diff --git a/api/include/opentelemetry/metrics_new/provider.h b/api/include/opentelemetry/metrics/provider.h
similarity index 77%
rename from api/include/opentelemetry/metrics_new/provider.h
rename to api/include/opentelemetry/metrics/provider.h
index d8feeaa1f3..3bacac9760 100644
--- a/api/include/opentelemetry/metrics_new/provider.h
+++ b/api/include/opentelemetry/metrics/provider.h
@@ -2,15 +2,17 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #pragma once
-#include <mutex>
+#ifndef ENABLE_METRICS_PREVIEW
 
-#include "opentelemetry/common/spin_lock_mutex.h"
-#include "opentelemetry/metrics_new/meter_provider.h"
-#include "opentelemetry/metrics_new/noop.h"
-#include "opentelemetry/nostd/shared_ptr.h"
+#  include <mutex>
+
+#  include "opentelemetry/common/spin_lock_mutex.h"
+#  include "opentelemetry/metrics/meter_provider.h"
+#  include "opentelemetry/metrics/noop.h"
+#  include "opentelemetry/nostd/shared_ptr.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
-namespace metrics_new
+namespace metrics
 {
 /**
  * Stores the singleton global MeterProvider.
@@ -53,5 +55,6 @@ class Provider
   }
 };
 
-}  // namespace metrics_new
-OPENTELEMETRY_END_NAMESPACE
\ No newline at end of file
+}  // namespace metrics
+OPENTELEMETRY_END_NAMESPACE
+#endif
\ No newline at end of file
diff --git a/api/include/opentelemetry/metrics_new/sync_instruments.h b/api/include/opentelemetry/metrics/sync_instruments.h
similarity index 98%
rename from api/include/opentelemetry/metrics_new/sync_instruments.h
rename to api/include/opentelemetry/metrics/sync_instruments.h
index f0fcc8ab1d..9c8a776672 100644
--- a/api/include/opentelemetry/metrics_new/sync_instruments.h
+++ b/api/include/opentelemetry/metrics/sync_instruments.h
@@ -10,7 +10,7 @@
 #  include "opentelemetry/nostd/string_view.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
-namespace metrics_new
+namespace metrics
 {
 
 class SynchronousInstrument
@@ -129,6 +129,6 @@ class UpDownCounter : public SynchronousInstrument
   }
 };
 
-}  // namespace metrics_new
+}  // namespace metrics
 OPENTELEMETRY_END_NAMESPACE
 #endif
diff --git a/api/test/metrics_new/CMakeLists.txt b/api/test/metrics/CMakeLists.txt
similarity index 100%
rename from api/test/metrics_new/CMakeLists.txt
rename to api/test/metrics/CMakeLists.txt
diff --git a/api/test/metrics_new/meter_provider_test.cc b/api/test/metrics/meter_provider_test.cc
similarity index 66%
rename from api/test/metrics_new/meter_provider_test.cc
rename to api/test/metrics/meter_provider_test.cc
index 0df7cda65c..161d852f09 100644
--- a/api/test/metrics_new/meter_provider_test.cc
+++ b/api/test/metrics/meter_provider_test.cc
@@ -1,15 +1,17 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-#include <gtest/gtest.h>
-#include "opentelemetry/metrics_new/noop.h"
-#include "opentelemetry/metrics_new/provider.h"
-#include "opentelemetry/nostd/shared_ptr.h"
+#ifndef ENABLE_METRICS_PREVIEW
 
-using opentelemetry::metrics_new::Meter;
-using opentelemetry::metrics_new::MeterProvider;
-using opentelemetry::metrics_new::NoopMeterProvider;
-using opentelemetry::metrics_new::Provider;
+#  include <gtest/gtest.h>
+#  include "opentelemetry/metrics/noop.h"
+#  include "opentelemetry/metrics/provider.h"
+#  include "opentelemetry/nostd/shared_ptr.h"
+
+using opentelemetry::metrics::Meter;
+using opentelemetry::metrics::MeterProvider;
+using opentelemetry::metrics::NoopMeterProvider;
+using opentelemetry::metrics::Provider;
 
 TEST(Provider, GetMeterProviderDefault)
 {
@@ -33,3 +35,4 @@ TEST(Provider, MultipleMeterProviders)
 
   ASSERT_NE(Provider::GetMeterProvider(), tf);
 }
+#endif
diff --git a/api/test/metrics_new/noop_sync_instrument_test.cc b/api/test/metrics/noop_sync_instrument_test.cc
similarity index 60%
rename from api/test/metrics_new/noop_sync_instrument_test.cc
rename to api/test/metrics/noop_sync_instrument_test.cc
index 4922d9273d..4597e79e8b 100644
--- a/api/test/metrics_new/noop_sync_instrument_test.cc
+++ b/api/test/metrics/noop_sync_instrument_test.cc
@@ -1,14 +1,16 @@
 // Copyright The OpenTelemetry Authors
 // SPDX-License-Identifier: Apache-2.0
 
-#include <gtest/gtest.h>
-#include <map>
-#include "opentelemetry/metrics_new/noop.h"
+#ifndef ENABLE_METRICS_PREVIEW
+
+#  include <gtest/gtest.h>
+#  include <map>
+#  include "opentelemetry/metrics/noop.h"
 
 TEST(Counter, Add)
 {
-  std::shared_ptr<opentelemetry::metrics_new::Counter<long>> counter{
-      new opentelemetry::metrics_new::NoopCounter<long>("test", "none", "unitless")};
+  std::shared_ptr<opentelemetry::metrics::Counter<long>> counter{
+      new opentelemetry::metrics::NoopCounter<long>("test", "none", "unitless")};
 
   std::map<std::string, std::string> labels = {{"k1", "v1"}};
   EXPECT_NO_THROW(counter->Add(10l, labels));
@@ -18,8 +20,8 @@ TEST(Counter, Add)
 
 TEST(histogram, Record)
 {
-  std::shared_ptr<opentelemetry::metrics_new::Histogram<long>> counter{
-      new opentelemetry::metrics_new::NoopHistogram<long>("test", "none", "unitless")};
+  std::shared_ptr<opentelemetry::metrics::Histogram<long>> counter{
+      new opentelemetry::metrics::NoopHistogram<long>("test", "none", "unitless")};
 
   std::map<std::string, std::string> labels = {{"k1", "v1"}};
   EXPECT_NO_THROW(counter->Record(10l, labels));
@@ -29,11 +31,13 @@ TEST(histogram, Record)
 
 TEST(UpDownCountr, Record)
 {
-  std::shared_ptr<opentelemetry::metrics_new::UpDownCounter<long>> counter{
-      new opentelemetry::metrics_new::NoopUpDownCounter<long>("test", "none", "unitless")};
+  std::shared_ptr<opentelemetry::metrics::UpDownCounter<long>> counter{
+      new opentelemetry::metrics::NoopUpDownCounter<long>("test", "none", "unitless")};
 
   std::map<std::string, std::string> labels = {{"k1", "v1"}};
   EXPECT_NO_THROW(counter->Add(10l, labels));
   EXPECT_NO_THROW(counter->Add(2l));
   EXPECT_NO_THROW(counter->Add(10l, {{"k1", "1"}, {"k2", 2}}));
-}
\ No newline at end of file
+}
+
+#endif
\ No newline at end of file

From 93341e23444474435f5187e259f94de58c7708b5 Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Tue, 9 Nov 2021 21:49:45 -0800
Subject: [PATCH 11/14] fix async meter

---
 api/include/opentelemetry/metrics/meter.h | 36 -----------------------
 1 file changed, 36 deletions(-)

diff --git a/api/include/opentelemetry/metrics/meter.h b/api/include/opentelemetry/metrics/meter.h
index a56e1c3417..4978c834fc 100644
--- a/api/include/opentelemetry/metrics/meter.h
+++ b/api/include/opentelemetry/metrics/meter.h
@@ -63,24 +63,12 @@ class Meter
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept = 0;
 
-  virtual nostd::shared_ptr<ObservableCounter<long>> CreateLongObservableCounter(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<long> &, const common::KeyValueIterable &),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
-
   virtual nostd::shared_ptr<ObservableCounter<double>> CreateDoubleObservableCounter(
       nostd::string_view name,
       void (*callback)(ObserverResult<double> &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept = 0;
 
-  virtual nostd::shared_ptr<ObservableCounter<double>> CreateDoubleObservableCounter(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<double> &, const common::KeyValueIterable &),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
-
   /**
    * Creates a Histogram with the passed characteristics and returns a shared_ptr to that Histogram.
    *
@@ -116,24 +104,12 @@ class Meter
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept = 0;
 
-  virtual nostd::shared_ptr<ObservableGauge<long>> CreateLongObservableGauge(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<long> &, const common::KeyValueIterable &),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
-
   virtual nostd::shared_ptr<ObservableGauge<double>> CreateDoubleObservableGauge(
       nostd::string_view name,
       void (*callback)(ObserverResult<double> &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept = 0;
 
-  virtual nostd::shared_ptr<ObservableGauge<double>> CreateDoubleObservableGauge(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<double> &, const common::KeyValueIterable &),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
-
   /**
    * Creates an UpDownCounter with the passed characteristics and returns a shared_ptr to that
    * UpDownCounter.
@@ -170,23 +146,11 @@ class Meter
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept = 0;
 
-  virtual nostd::shared_ptr<ObservableUpDownCounter<long>> CreateLongObservableUpDownCounter(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<long> &, const common::KeyValueIterable &),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
-
   virtual nostd::shared_ptr<ObservableUpDownCounter<double>> CreateDoubleObservableUpDownCounter(
       nostd::string_view name,
       void (*callback)(ObserverResult<double> &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept = 0;
-
-  virtual nostd::shared_ptr<ObservableUpDownCounter<double>> CreateDoubleObservableUpDownCounter(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<double> &, const common::KeyValueIterable &),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
 };
 }  // namespace metrics
 OPENTELEMETRY_END_NAMESPACE

From 96ee875c475e1f3a6013973f8b83194b261857a4 Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Tue, 9 Nov 2021 21:51:43 -0800
Subject: [PATCH 12/14] update comment

---
 api/include/opentelemetry/metrics/meter.h | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/api/include/opentelemetry/metrics/meter.h b/api/include/opentelemetry/metrics/meter.h
index 4978c834fc..9f7f2d2b0a 100644
--- a/api/include/opentelemetry/metrics/meter.h
+++ b/api/include/opentelemetry/metrics/meter.h
@@ -53,8 +53,7 @@ class Meter
    * @param name the name of the new Observable Counter.
    * @param description a brief description of what the Observable Counter is used for.
    * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
-   * @param callback the function to be observed by the instrument. This can optionally take `state`
-   * as key-value argument.
+   * @param callback the function to be observed by the instrument.
    * @return a shared pointer to the created Observable Counter.
    */
   virtual nostd::shared_ptr<ObservableCounter<long>> CreateLongObservableCounter(
@@ -94,8 +93,7 @@ class Meter
    * @param name the name of the new Observable Gauge.
    * @param description a brief description of what the Observable Gauge is used for.
    * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
-   * @param callback the function to be observed by the instrument. This can optionally take `state`
-   * as key-value argument.
+   * @param callback the function to be observed by the instrument.
    * @return a shared pointer to the created Observable Gauge.
    */
   virtual nostd::shared_ptr<ObservableGauge<long>> CreateLongObservableGauge(
@@ -136,8 +134,7 @@ class Meter
    * @param name the name of the new Observable UpDownCounter.
    * @param description a brief description of what the Observable UpDownCounter is used for.
    * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
-   * @param callback the function to be observed by the instrument. This can optionally take `state`
-   * as key-value argument.
+   * @param callback the function to be observed by the instrument.
    * @return a shared pointer to the created Observable UpDownCounter.
    */
   virtual nostd::shared_ptr<ObservableUpDownCounter<long>> CreateLongObservableUpDownCounter(

From d17ea27ba6bcd9e674a0e08244e9c281c49ed71d Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Tue, 9 Nov 2021 22:15:43 -0800
Subject: [PATCH 13/14] build failure

---
 api/include/opentelemetry/metrics/noop.h | 60 ------------------------
 1 file changed, 60 deletions(-)

diff --git a/api/include/opentelemetry/metrics/noop.h b/api/include/opentelemetry/metrics/noop.h
index f596c94f39..19b9443a7d 100644
--- a/api/include/opentelemetry/metrics/noop.h
+++ b/api/include/opentelemetry/metrics/noop.h
@@ -134,16 +134,6 @@ class NoopMeter final : public Meter
         new NoopObservableCounter<long>(name, callback, description, unit)};
   }
 
-  nostd::shared_ptr<ObservableCounter<long>> CreateLongObservableCounter(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<long> &, const common::KeyValueIterable &),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept override
-  {
-    return nostd::shared_ptr<ObservableCounter<long>>{
-        new NoopObservableCounter<long>(name, callback, description, unit)};
-  }
-
   nostd::shared_ptr<ObservableCounter<double>> CreateDoubleObservableCounter(
       nostd::string_view name,
       void (*callback)(ObserverResult<double> &),
@@ -154,16 +144,6 @@ class NoopMeter final : public Meter
         new NoopObservableCounter<double>(name, callback, description, unit)};
   }
 
-  nostd::shared_ptr<ObservableCounter<double>> CreateDoubleObservableCounter(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<double> &, const common::KeyValueIterable &),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept override
-  {
-    return nostd::shared_ptr<ObservableCounter<double>>{
-        new NoopObservableCounter<double>(name, callback, description, unit)};
-  }
-
   nostd::shared_ptr<Histogram<long>> CreateLongHistogram(
       nostd::string_view name,
       nostd::string_view description = "",
@@ -190,16 +170,6 @@ class NoopMeter final : public Meter
         new NoopObservableGauge<long>(name, callback, description, unit)};
   }
 
-  nostd::shared_ptr<ObservableGauge<long>> CreateLongObservableGauge(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<long> &, const common::KeyValueIterable &),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept override
-  {
-    return nostd::shared_ptr<ObservableGauge<long>>{
-        new NoopObservableGauge<long>(name, callback, description, unit)};
-  }
-
   nostd::shared_ptr<ObservableGauge<double>> CreateDoubleObservableGauge(
       nostd::string_view name,
       void (*callback)(ObserverResult<double> &),
@@ -210,16 +180,6 @@ class NoopMeter final : public Meter
         new NoopObservableGauge<double>(name, callback, description, unit)};
   }
 
-  nostd::shared_ptr<ObservableGauge<double>> CreateDoubleObservableGauge(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<double> &, const common::KeyValueIterable &),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept override
-  {
-    return nostd::shared_ptr<ObservableGauge<double>>{
-        new NoopObservableGauge<double>(name, callback, description, unit)};
-  }
-
   nostd::shared_ptr<UpDownCounter<long>> CreateLongUpDownCounter(
       nostd::string_view name,
       nostd::string_view description = "",
@@ -248,16 +208,6 @@ class NoopMeter final : public Meter
         new NoopObservableUpDownCounter<long>(name, callback, description, unit)};
   }
 
-  nostd::shared_ptr<ObservableUpDownCounter<long>> CreateLongObservableUpDownCounter(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<long> &, const common::KeyValueIterable &),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept override
-  {
-    return nostd::shared_ptr<ObservableUpDownCounter<long>>{
-        new NoopObservableUpDownCounter<long>(name, callback, description, unit)};
-  }
-
   nostd::shared_ptr<ObservableUpDownCounter<double>> CreateDoubleObservableUpDownCounter(
       nostd::string_view name,
       void (*callback)(ObserverResult<double> &),
@@ -267,16 +217,6 @@ class NoopMeter final : public Meter
     return nostd::shared_ptr<ObservableUpDownCounter<double>>{
         new NoopObservableUpDownCounter<double>(name, callback, description, unit)};
   }
-
-  nostd::shared_ptr<ObservableUpDownCounter<double>> CreateDoubleObservableUpDownCounter(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<double> &, const common::KeyValueIterable &),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept override
-  {
-    return nostd::shared_ptr<ObservableUpDownCounter<double>>{
-        new NoopObservableUpDownCounter<double>(name, callback, description, unit)};
-  }
 };
 
 /**

From 5736834765fcdf020e761beb8b1c861d898ce4ee Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Wed, 10 Nov 2021 15:16:54 -0800
Subject: [PATCH 14/14] make default unit to 1

---
 api/include/opentelemetry/metrics/meter.h | 24 +++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/api/include/opentelemetry/metrics/meter.h b/api/include/opentelemetry/metrics/meter.h
index 9f7f2d2b0a..cd176d3157 100644
--- a/api/include/opentelemetry/metrics/meter.h
+++ b/api/include/opentelemetry/metrics/meter.h
@@ -39,12 +39,12 @@ class Meter
   virtual nostd::shared_ptr<Counter<long>> CreateLongCounter(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
+      nostd::string_view unit        = "1") noexcept = 0;
 
   virtual nostd::shared_ptr<Counter<double>> CreateDoubleCounter(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
+      nostd::string_view unit        = "1") noexcept = 0;
 
   /**
    * Creates a Asynchronouse (Observable) counter with the passed characteristics and returns a
@@ -60,13 +60,13 @@ class Meter
       nostd::string_view name,
       void (*callback)(ObserverResult<long> &),
       nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
+      nostd::string_view unit        = "1") noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableCounter<double>> CreateDoubleObservableCounter(
       nostd::string_view name,
       void (*callback)(ObserverResult<double> &),
       nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
+      nostd::string_view unit        = "1") noexcept = 0;
 
   /**
    * Creates a Histogram with the passed characteristics and returns a shared_ptr to that Histogram.
@@ -79,12 +79,12 @@ class Meter
   virtual nostd::shared_ptr<Histogram<long>> CreateLongHistogram(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
+      nostd::string_view unit        = "1") noexcept = 0;
 
   virtual nostd::shared_ptr<Histogram<double>> CreateDoubleHistogram(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
+      nostd::string_view unit        = "1") noexcept = 0;
 
   /**
    * Creates a Asynchronouse (Observable) Gauge with the passed characteristics and returns a
@@ -100,13 +100,13 @@ class Meter
       nostd::string_view name,
       void (*callback)(ObserverResult<long> &),
       nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
+      nostd::string_view unit        = "1") noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableGauge<double>> CreateDoubleObservableGauge(
       nostd::string_view name,
       void (*callback)(ObserverResult<double> &),
       nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
+      nostd::string_view unit        = "1") noexcept = 0;
 
   /**
    * Creates an UpDownCounter with the passed characteristics and returns a shared_ptr to that
@@ -120,12 +120,12 @@ class Meter
   virtual nostd::shared_ptr<UpDownCounter<long>> CreateLongUpDownCounter(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
+      nostd::string_view unit        = "1") noexcept = 0;
 
   virtual nostd::shared_ptr<UpDownCounter<double>> CreateDoubleUpDownCounter(
       nostd::string_view name,
       nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
+      nostd::string_view unit        = "1") noexcept = 0;
 
   /**
    * Creates a Asynchronouse (Observable) UpDownCounter with the passed characteristics and returns
@@ -141,13 +141,13 @@ class Meter
       nostd::string_view name,
       void (*callback)(ObserverResult<long> &),
       nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
+      nostd::string_view unit        = "1") noexcept = 0;
 
   virtual nostd::shared_ptr<ObservableUpDownCounter<double>> CreateDoubleObservableUpDownCounter(
       nostd::string_view name,
       void (*callback)(ObserverResult<double> &),
       nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
+      nostd::string_view unit        = "1") noexcept = 0;
 };
 }  // namespace metrics
 OPENTELEMETRY_END_NAMESPACE