From 55f5572dc189a5657a97dc4fea19abf11e257bd7 Mon Sep 17 00:00:00 2001
From: Lalit Kumar Bhasin <lalit_fin@yahoo.com>
Date: Tue, 10 May 2022 16:28:52 -0700
Subject: [PATCH 1/5] intgrate async storage with async instrument

---
 api/include/opentelemetry/metrics/meter.h     | 56 +++++------
 api/include/opentelemetry/metrics/noop.h      | 84 ++++++----------
 sdk/include/opentelemetry/sdk/metrics/meter.h | 55 +++++++----
 sdk/src/metrics/meter.cc                      | 96 +++++++++++--------
 4 files changed, 145 insertions(+), 146 deletions(-)

diff --git a/api/include/opentelemetry/metrics/meter.h b/api/include/opentelemetry/metrics/meter.h
index 9f7f2d2b0a..6a19911390 100644
--- a/api/include/opentelemetry/metrics/meter.h
+++ b/api/include/opentelemetry/metrics/meter.h
@@ -56,17 +56,15 @@ class Meter
    * @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(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<long> &),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
+  virtual void CreateLongObservableCounter(nostd::string_view name,
+                                           void (*callback)(ObserverResult<long> &),
+                                           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 void CreateDoubleObservableCounter(nostd::string_view name,
+                                             void (*callback)(ObserverResult<double> &),
+                                             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.
@@ -96,17 +94,15 @@ class Meter
    * @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(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<long> &),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept = 0;
+  virtual void CreateLongObservableGauge(nostd::string_view name,
+                                         void (*callback)(ObserverResult<long> &),
+                                         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 void CreateDoubleObservableGauge(nostd::string_view name,
+                                           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
@@ -137,17 +133,15 @@ class Meter
    * @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(
-      nostd::string_view name,
-      void (*callback)(ObserverResult<long> &),
-      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 void CreateLongObservableUpDownCounter(nostd::string_view name,
+                                                 void (*callback)(ObserverResult<long> &),
+                                                 nostd::string_view description = "",
+                                                 nostd::string_view unit        = "") noexcept = 0;
+
+  virtual void CreateDoubleObservableUpDownCounter(nostd::string_view name,
+                                                   void (*callback)(ObserverResult<double> &),
+                                                   nostd::string_view description = "",
+                                                   nostd::string_view unit = "") noexcept = 0;
 };
 }  // namespace metrics
 OPENTELEMETRY_END_NAMESPACE
diff --git a/api/include/opentelemetry/metrics/noop.h b/api/include/opentelemetry/metrics/noop.h
index 3332384ee2..0fbda060b9 100644
--- a/api/include/opentelemetry/metrics/noop.h
+++ b/api/include/opentelemetry/metrics/noop.h
@@ -137,25 +137,17 @@ class NoopMeter final : public Meter
     return nostd::shared_ptr<Counter<double>>{new NoopCounter<double>(name, description, unit)};
   }
 
-  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 CreateLongObservableCounter(nostd::string_view name,
+                                   void (*callback)(ObserverResult<long> &),
+                                   nostd::string_view description = "",
+                                   nostd::string_view unit        = "") 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)};
-  }
+  void CreateDoubleObservableCounter(nostd::string_view name,
+                                     void (*callback)(ObserverResult<double> &),
+                                     nostd::string_view description = "",
+                                     nostd::string_view unit        = "") noexcept override
+  {}
 
   nostd::shared_ptr<Histogram<long>> CreateLongHistogram(
       nostd::string_view name,
@@ -173,25 +165,17 @@ class NoopMeter final : public Meter
     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)};
-  }
+  void CreateLongObservableGauge(nostd::string_view name,
+                                 void (*callback)(ObserverResult<long> &),
+                                 nostd::string_view description = "",
+                                 nostd::string_view unit        = "") noexcept override
+  {}
 
-  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)};
-  }
+  void CreateDoubleObservableGauge(nostd::string_view name,
+                                   void (*callback)(ObserverResult<double> &),
+                                   nostd::string_view description = "",
+                                   nostd::string_view unit        = "") noexcept override
+  {}
 
   nostd::shared_ptr<UpDownCounter<long>> CreateLongUpDownCounter(
       nostd::string_view name,
@@ -211,25 +195,17 @@ class NoopMeter final : public Meter
         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)};
-  }
+  void CreateLongObservableUpDownCounter(nostd::string_view name,
+                                         void (*callback)(ObserverResult<long> &),
+                                         nostd::string_view description = "",
+                                         nostd::string_view unit        = "") noexcept override
+  {}
 
-  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)};
-  }
+  void CreateDoubleObservableUpDownCounter(nostd::string_view name,
+                                           void (*callback)(ObserverResult<double> &),
+                                           nostd::string_view description = "",
+                                           nostd::string_view unit        = "") noexcept override
+  {}
 };
 
 /**
diff --git a/sdk/include/opentelemetry/sdk/metrics/meter.h b/sdk/include/opentelemetry/sdk/metrics/meter.h
index 4a6ea26aeb..8e3295e1d3 100644
--- a/sdk/include/opentelemetry/sdk/metrics/meter.h
+++ b/sdk/include/opentelemetry/sdk/metrics/meter.h
@@ -8,6 +8,8 @@
 #  include "opentelemetry/sdk/instrumentationlibrary/instrumentation_library.h"
 #  include "opentelemetry/sdk/metrics/instruments.h"
 #  include "opentelemetry/sdk/metrics/meter_context.h"
+#  include "opentelemetry/sdk/metrics/state/async_metric_storage.h"
+
 #  include "opentelemetry/sdk/resource/resource.h"
 #  include "opentelemetry/version.h"
 
@@ -40,17 +42,16 @@ class Meter final : public opentelemetry::metrics::Meter
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept override;
 
-  nostd::shared_ptr<opentelemetry::metrics::ObservableCounter<long>> CreateLongObservableCounter(
+  void CreateLongObservableCounter(nostd::string_view name,
+                                   void (*callback)(opentelemetry::metrics::ObserverResult<long> &),
+                                   nostd::string_view description = "",
+                                   nostd::string_view unit        = "") noexcept override;
+
+  void CreateDoubleObservableCounter(
       nostd::string_view name,
-      void (*callback)(opentelemetry::metrics::ObserverResult<long> &),
+      void (*callback)(opentelemetry::metrics::ObserverResult<double> &),
       nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept override;
-
-  nostd::shared_ptr<opentelemetry::metrics::ObservableCounter<double>>
-  CreateDoubleObservableCounter(nostd::string_view name,
-                                void (*callback)(opentelemetry::metrics::ObserverResult<double> &),
-                                nostd::string_view description = "",
-                                nostd::string_view unit        = "1") noexcept override;
+      nostd::string_view unit        = "1") noexcept override;
 
   nostd::shared_ptr<opentelemetry::metrics::Histogram<long>> CreateLongHistogram(
       nostd::string_view name,
@@ -62,13 +63,12 @@ class Meter final : public opentelemetry::metrics::Meter
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept override;
 
-  nostd::shared_ptr<opentelemetry::metrics::ObservableGauge<long>> CreateLongObservableGauge(
-      nostd::string_view name,
-      void (*callback)(opentelemetry::metrics::ObserverResult<long> &),
-      nostd::string_view description = "",
-      nostd::string_view unit        = "") noexcept override;
+  void CreateLongObservableGauge(nostd::string_view name,
+                                 void (*callback)(opentelemetry::metrics::ObserverResult<long> &),
+                                 nostd::string_view description = "",
+                                 nostd::string_view unit        = "") noexcept override;
 
-  nostd::shared_ptr<opentelemetry::metrics::ObservableGauge<double>> CreateDoubleObservableGauge(
+  void CreateDoubleObservableGauge(
       nostd::string_view name,
       void (*callback)(opentelemetry::metrics::ObserverResult<double> &),
       nostd::string_view description = "",
@@ -84,15 +84,13 @@ class Meter final : public opentelemetry::metrics::Meter
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept override;
 
-  nostd::shared_ptr<opentelemetry::metrics::ObservableUpDownCounter<long>>
-  CreateLongObservableUpDownCounter(
+  void CreateLongObservableUpDownCounter(
       nostd::string_view name,
       void (*callback)(opentelemetry::metrics::ObserverResult<long> &),
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept override;
 
-  nostd::shared_ptr<opentelemetry::metrics::ObservableUpDownCounter<double>>
-  CreateDoubleObservableUpDownCounter(
+  void CreateDoubleObservableUpDownCounter(
       nostd::string_view name,
       void (*callback)(opentelemetry::metrics::ObserverResult<double> &),
       nostd::string_view description = "",
@@ -116,6 +114,25 @@ class Meter final : public opentelemetry::metrics::Meter
 
   std::unique_ptr<WritableMetricStorage> RegisterMetricStorage(
       InstrumentDescriptor &instrument_descriptor);
+
+  template <class T>
+  void RegisterAsyncMetricStorage(InstrumentDescriptor &instrument_descriptor,
+                                  void (*callback)(opentelemetry::metrics::ObserverResult<T> &))
+  {
+    auto view_registry = meter_context_->GetViewRegistry();
+    auto success       = view_registry->FindViews(
+        instrument_descriptor, *instrumentation_library_,
+        [this, &instrument_descriptor, callback](const View &view) {
+          auto view_instr_desc         = instrument_descriptor;
+          view_instr_desc.name_        = view.GetName();
+          view_instr_desc.description_ = view.GetDescription();
+          auto storage                 = std::shared_ptr<AsyncMetricStorage<T>>(
+              new AsyncMetricStorage<T>(view_instr_desc, view.GetAggregationType(), callback,
+                                        &view.GetAttributesProcessor()));
+          storage_registry_[instrument_descriptor.name_] = storage;
+          return true;
+        });
+  }
 };
 }  // namespace metrics
 }  // namespace sdk
diff --git a/sdk/src/metrics/meter.cc b/sdk/src/metrics/meter.cc
index c0b0ce7a57..17250cc4a1 100644
--- a/sdk/src/metrics/meter.cc
+++ b/sdk/src/metrics/meter.cc
@@ -57,24 +57,28 @@ nostd::shared_ptr<metrics::Counter<double>> Meter::CreateDoubleCounter(
       new DoubleCounter(instrument_descriptor, std::move(storage))};
 }
 
-nostd::shared_ptr<metrics::ObservableCounter<long>> Meter::CreateLongObservableCounter(
-    nostd::string_view name,
-    void (*callback)(metrics::ObserverResult<long> &),
-    nostd::string_view description,
-    nostd::string_view unit) noexcept
+void Meter::CreateLongObservableCounter(nostd::string_view name,
+                                        void (*callback)(metrics::ObserverResult<long> &),
+                                        nostd::string_view description,
+                                        nostd::string_view unit) noexcept
 {
-  return nostd::shared_ptr<metrics::ObservableCounter<long>>{
-      new LongObservableCounter(name, callback, description, unit)};
+  InstrumentDescriptor instrument_descriptor = {
+      std::string{name.data(), name.size()}, std::string{description.data(), description.size()},
+      std::string{unit.data(), unit.size()}, InstrumentType::kObservableGauge,
+      InstrumentValueType::kLong};
+  RegisterAsyncMetricStorage<long>(instrument_descriptor, callback);
 }
 
-nostd::shared_ptr<metrics::ObservableCounter<double>> Meter::CreateDoubleObservableCounter(
-    nostd::string_view name,
-    void (*callback)(metrics::ObserverResult<double> &),
-    nostd::string_view description,
-    nostd::string_view unit) noexcept
+void Meter::CreateDoubleObservableCounter(nostd::string_view name,
+                                          void (*callback)(metrics::ObserverResult<double> &),
+                                          nostd::string_view description,
+                                          nostd::string_view unit) noexcept
 {
-  return nostd::shared_ptr<metrics::ObservableCounter<double>>{
-      new DoubleObservableCounter(name, callback, description, unit)};
+  InstrumentDescriptor instrument_descriptor = {
+      std::string{name.data(), name.size()}, std::string{description.data(), description.size()},
+      std::string{unit.data(), unit.size()}, InstrumentType::kObservableGauge,
+      InstrumentValueType::kDouble};
+  RegisterAsyncMetricStorage<double>(instrument_descriptor, callback);
 }
 
 nostd::shared_ptr<metrics::Histogram<long>> Meter::CreateLongHistogram(
@@ -105,24 +109,28 @@ nostd::shared_ptr<metrics::Histogram<double>> Meter::CreateDoubleHistogram(
       new DoubleHistogram(instrument_descriptor, std::move(storage))};
 }
 
-nostd::shared_ptr<metrics::ObservableGauge<long>> Meter::CreateLongObservableGauge(
-    nostd::string_view name,
-    void (*callback)(metrics::ObserverResult<long> &),
-    nostd::string_view description,
-    nostd::string_view unit) noexcept
+void Meter::CreateLongObservableGauge(nostd::string_view name,
+                                      void (*callback)(metrics::ObserverResult<long> &),
+                                      nostd::string_view description,
+                                      nostd::string_view unit) noexcept
 {
-  return nostd::shared_ptr<metrics::ObservableGauge<long>>{
-      new LongObservableGauge(name, callback, description, unit)};
+  InstrumentDescriptor instrument_descriptor = {
+      std::string{name.data(), name.size()}, std::string{description.data(), description.size()},
+      std::string{unit.data(), unit.size()}, InstrumentType::kObservableGauge,
+      InstrumentValueType::kLong};
+  RegisterAsyncMetricStorage<long>(instrument_descriptor, callback);
 }
 
-nostd::shared_ptr<metrics::ObservableGauge<double>> Meter::CreateDoubleObservableGauge(
-    nostd::string_view name,
-    void (*callback)(metrics::ObserverResult<double> &),
-    nostd::string_view description,
-    nostd::string_view unit) noexcept
+void Meter::CreateDoubleObservableGauge(nostd::string_view name,
+                                        void (*callback)(metrics::ObserverResult<double> &),
+                                        nostd::string_view description,
+                                        nostd::string_view unit) noexcept
 {
-  return nostd::shared_ptr<metrics::ObservableGauge<double>>{
-      new DoubleObservableGauge(name, callback, description, unit)};
+  InstrumentDescriptor instrument_descriptor = {
+      std::string{name.data(), name.size()}, std::string{description.data(), description.size()},
+      std::string{unit.data(), unit.size()}, InstrumentType::kObservableGauge,
+      InstrumentValueType::kDouble};
+  RegisterAsyncMetricStorage<double>(instrument_descriptor, callback);
 }
 
 nostd::shared_ptr<metrics::UpDownCounter<long>> Meter::CreateLongUpDownCounter(
@@ -153,24 +161,28 @@ nostd::shared_ptr<metrics::UpDownCounter<double>> Meter::CreateDoubleUpDownCount
       new DoubleUpDownCounter(instrument_descriptor, std::move(storage))};
 }
 
-nostd::shared_ptr<metrics::ObservableUpDownCounter<long>> Meter::CreateLongObservableUpDownCounter(
-    nostd::string_view name,
-    void (*callback)(metrics::ObserverResult<long> &),
-    nostd::string_view description,
-    nostd::string_view unit) noexcept
+void Meter::CreateLongObservableUpDownCounter(nostd::string_view name,
+                                              void (*callback)(metrics::ObserverResult<long> &),
+                                              nostd::string_view description,
+                                              nostd::string_view unit) noexcept
 {
-  return nostd::shared_ptr<metrics::ObservableUpDownCounter<long>>{
-      new LongObservableUpDownCounter(name, callback, description, unit)};
+  InstrumentDescriptor instrument_descriptor = {
+      std::string{name.data(), name.size()}, std::string{description.data(), description.size()},
+      std::string{unit.data(), unit.size()}, InstrumentType::kObservableUpDownCounter,
+      InstrumentValueType::kLong};
+  RegisterAsyncMetricStorage<long>(instrument_descriptor, callback);
 }
 
-nostd::shared_ptr<metrics::ObservableUpDownCounter<double>>
-Meter::CreateDoubleObservableUpDownCounter(nostd::string_view name,
-                                           void (*callback)(metrics::ObserverResult<double> &),
-                                           nostd::string_view description,
-                                           nostd::string_view unit) noexcept
+void Meter::CreateDoubleObservableUpDownCounter(nostd::string_view name,
+                                                void (*callback)(metrics::ObserverResult<double> &),
+                                                nostd::string_view description,
+                                                nostd::string_view unit) noexcept
 {
-  return nostd::shared_ptr<metrics::ObservableUpDownCounter<double>>{
-      new DoubleObservableUpDownCounter(name, callback, description, unit)};
+  InstrumentDescriptor instrument_descriptor = {
+      std::string{name.data(), name.size()}, std::string{description.data(), description.size()},
+      std::string{unit.data(), unit.size()}, InstrumentType::kObservableUpDownCounter,
+      InstrumentValueType::kDouble};
+  RegisterAsyncMetricStorage<double>(instrument_descriptor, callback);
 }
 
 const sdk::instrumentationlibrary::InstrumentationLibrary *Meter::GetInstrumentationLibrary()

From af087dbd9ca9b93f7a75a0fd05879d221861e677 Mon Sep 17 00:00:00 2001
From: Lalit Kumar Bhasin <lalit_fin@yahoo.com>
Date: Tue, 10 May 2022 18:08:03 -0700
Subject: [PATCH 2/5] add example

---
 .../common/metrics_foo_library/foo_library.cc | 22 +++++++++++++++++++
 .../common/metrics_foo_library/foo_library.h  |  1 +
 2 files changed, 23 insertions(+)

diff --git a/examples/common/metrics_foo_library/foo_library.cc b/examples/common/metrics_foo_library/foo_library.cc
index cd15adad5b..6ee75c9417 100644
--- a/examples/common/metrics_foo_library/foo_library.cc
+++ b/examples/common/metrics_foo_library/foo_library.cc
@@ -13,6 +13,19 @@ namespace metrics_api = opentelemetry::metrics;
 
 namespace
 {
+
+class MeasurementFetcher
+{
+public:
+  static void Fetcher(opentelemetry::metrics::ObserverResult<long> &observer_result)
+  {
+    double val                                = (rand() % 700) + 1.1;
+    std::map<std::string, std::string> labels = get_random_attr();
+    auto labelkv = opentelemetry::common::KeyValueIterableView<decltype(labels)>{labels};
+    observer_result.Observe(val, labelkv);
+  }
+};
+
 std::map<std::string, std::string> get_random_attr()
 {
   static const std::vector<std::pair<std::string, std::string>> labels = {{"key1", "value1"},
@@ -23,6 +36,7 @@ std::map<std::string, std::string> get_random_attr()
   return std::map<std::string, std::string>{labels[rand() % (labels.size() - 1)],
                                             labels[rand() % (labels.size() - 1)]};
 }
+
 }  // namespace
 
 void foo_library::counter_example(const std::string &name)
@@ -40,6 +54,14 @@ void foo_library::counter_example(const std::string &name)
   }
 }
 
+void foo_library::observable_counter_example(const std::string &name)
+{
+  std::string counter_name                    = name + "_observable_counter";
+  auto provider                               = metrics_api::Provider::GetMeterProvider();
+  nostd::shared_ptr<metrics_api::Meter> meter = provider->GetMeter(name, "1.2.0");
+  auto double_observable_counter              = meter->CreateDoubleObservableCounter(counter_name);
+}
+
 void foo_library::histogram_example(const std::string &name)
 {
   std::string histogram_name                  = name + "_histogram";
diff --git a/examples/common/metrics_foo_library/foo_library.h b/examples/common/metrics_foo_library/foo_library.h
index 73cd30d2d5..19fd69a4c5 100644
--- a/examples/common/metrics_foo_library/foo_library.h
+++ b/examples/common/metrics_foo_library/foo_library.h
@@ -10,5 +10,6 @@ class foo_library
 public:
   static void counter_example(const std::string &name);
   static void histogram_example(const std::string &name);
+  static void guage_example(const std::string &name);
 };
 #endif

From 5db3275d0c98ee7ee66f6231de21a02bffdee248 Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Tue, 10 May 2022 20:53:54 -0700
Subject: [PATCH 3/5] fix example

---
 .../common/metrics_foo_library/foo_library.cc | 27 ++++++++++---------
 .../common/metrics_foo_library/foo_library.h  |  2 +-
 2 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/examples/common/metrics_foo_library/foo_library.cc b/examples/common/metrics_foo_library/foo_library.cc
index 6ee75c9417..1c0cd59ba3 100644
--- a/examples/common/metrics_foo_library/foo_library.cc
+++ b/examples/common/metrics_foo_library/foo_library.cc
@@ -6,6 +6,8 @@
 #  include <chrono>
 #  include <map>
 #  include <thread>
+#  include <vector>
+#  include "opentelemetry/context/context.h"
 #  include "opentelemetry/metrics/provider.h"
 
 namespace nostd       = opentelemetry::nostd;
@@ -14,18 +16,6 @@ namespace metrics_api = opentelemetry::metrics;
 namespace
 {
 
-class MeasurementFetcher
-{
-public:
-  static void Fetcher(opentelemetry::metrics::ObserverResult<long> &observer_result)
-  {
-    double val                                = (rand() % 700) + 1.1;
-    std::map<std::string, std::string> labels = get_random_attr();
-    auto labelkv = opentelemetry::common::KeyValueIterableView<decltype(labels)>{labels};
-    observer_result.Observe(val, labelkv);
-  }
-};
-
 std::map<std::string, std::string> get_random_attr()
 {
   static const std::vector<std::pair<std::string, std::string>> labels = {{"key1", "value1"},
@@ -37,6 +27,17 @@ std::map<std::string, std::string> get_random_attr()
                                             labels[rand() % (labels.size() - 1)]};
 }
 
+class MeasurementFetcher
+{
+public:
+  static void Fetcher(opentelemetry::metrics::ObserverResult<double> &observer_result)
+  {
+    double val                                = (rand() % 700) + 1.1;
+    std::map<std::string, std::string> labels = get_random_attr();
+    auto labelkv = opentelemetry::common::KeyValueIterableView<decltype(labels)>{labels};
+    observer_result.Observe(val, labelkv);
+  }
+};
 }  // namespace
 
 void foo_library::counter_example(const std::string &name)
@@ -59,7 +60,7 @@ void foo_library::observable_counter_example(const std::string &name)
   std::string counter_name                    = name + "_observable_counter";
   auto provider                               = metrics_api::Provider::GetMeterProvider();
   nostd::shared_ptr<metrics_api::Meter> meter = provider->GetMeter(name, "1.2.0");
-  auto double_observable_counter              = meter->CreateDoubleObservableCounter(counter_name);
+  meter->CreateDoubleObservableCounter(counter_name, MeasurementFetcher::Fetcher);
 }
 
 void foo_library::histogram_example(const std::string &name)
diff --git a/examples/common/metrics_foo_library/foo_library.h b/examples/common/metrics_foo_library/foo_library.h
index 19fd69a4c5..2f84bcc34f 100644
--- a/examples/common/metrics_foo_library/foo_library.h
+++ b/examples/common/metrics_foo_library/foo_library.h
@@ -10,6 +10,6 @@ class foo_library
 public:
   static void counter_example(const std::string &name);
   static void histogram_example(const std::string &name);
-  static void guage_example(const std::string &name);
+  static void observable_counter_example(const std::string &name);
 };
 #endif

From 0f9172f7bd69c8d1679fe9082155465222f1e3d4 Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Tue, 10 May 2022 21:50:04 -0700
Subject: [PATCH 4/5] more changes

---
 .../common/metrics_foo_library/foo_library.cc |  6 +++++-
 examples/metrics_simple/metrics_ostream.cc    | 19 +++++++++++++++++++
 sdk/include/opentelemetry/sdk/metrics/meter.h |  2 ++
 sdk/src/metrics/meter.cc                      |  4 ++--
 4 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/examples/common/metrics_foo_library/foo_library.cc b/examples/common/metrics_foo_library/foo_library.cc
index 1c0cd59ba3..79e0cbc5ab 100644
--- a/examples/common/metrics_foo_library/foo_library.cc
+++ b/examples/common/metrics_foo_library/foo_library.cc
@@ -35,7 +35,7 @@ class MeasurementFetcher
     double val                                = (rand() % 700) + 1.1;
     std::map<std::string, std::string> labels = get_random_attr();
     auto labelkv = opentelemetry::common::KeyValueIterableView<decltype(labels)>{labels};
-    observer_result.Observe(val, labelkv);
+    observer_result.Observe(val /*, labelkv*/);
   }
 };
 }  // namespace
@@ -61,6 +61,10 @@ void foo_library::observable_counter_example(const std::string &name)
   auto provider                               = metrics_api::Provider::GetMeterProvider();
   nostd::shared_ptr<metrics_api::Meter> meter = provider->GetMeter(name, "1.2.0");
   meter->CreateDoubleObservableCounter(counter_name, MeasurementFetcher::Fetcher);
+  while (true)
+  {
+    std::this_thread::sleep_for(std::chrono::milliseconds(500));
+  }
 }
 
 void foo_library::histogram_example(const std::string &name)
diff --git a/examples/metrics_simple/metrics_ostream.cc b/examples/metrics_simple/metrics_ostream.cc
index ebb8b34b8a..585856f91f 100644
--- a/examples/metrics_simple/metrics_ostream.cc
+++ b/examples/metrics_simple/metrics_ostream.cc
@@ -54,6 +54,18 @@ void initMetrics(const std::string &name)
       new metric_sdk::View{name, "description", metric_sdk::AggregationType::kSum}};
   p->AddView(std::move(instrument_selector), std::move(meter_selector), std::move(sum_view));
 
+  // observable counter view
+  std::string observable_counter_name = name + "_observable_counter";
+  std::unique_ptr<metric_sdk::InstrumentSelector> observable_instrument_selector{
+      new metric_sdk::InstrumentSelector(metric_sdk::InstrumentType::kObservableCounter,
+                                         observable_counter_name)};
+  std::unique_ptr<metric_sdk::MeterSelector> observable_meter_selector{
+      new metric_sdk::MeterSelector(name, version, schema)};
+  std::unique_ptr<metric_sdk::View> observable_sum_view{
+      new metric_sdk::View{name, "description", metric_sdk::AggregationType::kSum}};
+  p->AddView(std::move(observable_instrument_selector), std::move(observable_meter_selector),
+             std::move(observable_sum_view));
+
   // histogram view
   std::string histogram_name = name + "_histogram";
   std::unique_ptr<metric_sdk::InstrumentSelector> histogram_instrument_selector{
@@ -83,6 +95,10 @@ int main(int argc, char **argv)
   {
     foo_library::counter_example(name);
   }
+  else if (example_type == "observable_counter")
+  {
+    foo_library::observable_counter_example(name);
+  }
   else if (example_type == "histogram")
   {
     foo_library::histogram_example(name);
@@ -90,8 +106,11 @@ int main(int argc, char **argv)
   else
   {
     std::thread counter_example{&foo_library::counter_example, name};
+    std::thread observable_counter_example{&foo_library::observable_counter_example, name};
     std::thread histogram_example{&foo_library::histogram_example, name};
+
     counter_example.join();
+    observable_counter_example.join();
     histogram_example.join();
   }
 }
diff --git a/sdk/include/opentelemetry/sdk/metrics/meter.h b/sdk/include/opentelemetry/sdk/metrics/meter.h
index 8e3295e1d3..d9b2825d13 100644
--- a/sdk/include/opentelemetry/sdk/metrics/meter.h
+++ b/sdk/include/opentelemetry/sdk/metrics/meter.h
@@ -119,10 +119,12 @@ class Meter final : public opentelemetry::metrics::Meter
   void RegisterAsyncMetricStorage(InstrumentDescriptor &instrument_descriptor,
                                   void (*callback)(opentelemetry::metrics::ObserverResult<T> &))
   {
+    std::cout << "---LALIT--Register async\n";
     auto view_registry = meter_context_->GetViewRegistry();
     auto success       = view_registry->FindViews(
         instrument_descriptor, *instrumentation_library_,
         [this, &instrument_descriptor, callback](const View &view) {
+          std::cout << "--LALIT  Found view\n";
           auto view_instr_desc         = instrument_descriptor;
           view_instr_desc.name_        = view.GetName();
           view_instr_desc.description_ = view.GetDescription();
diff --git a/sdk/src/metrics/meter.cc b/sdk/src/metrics/meter.cc
index 9fe4429253..30725bdccf 100644
--- a/sdk/src/metrics/meter.cc
+++ b/sdk/src/metrics/meter.cc
@@ -64,7 +64,7 @@ void Meter::CreateLongObservableCounter(nostd::string_view name,
 {
   InstrumentDescriptor instrument_descriptor = {
       std::string{name.data(), name.size()}, std::string{description.data(), description.size()},
-      std::string{unit.data(), unit.size()}, InstrumentType::kObservableGauge,
+      std::string{unit.data(), unit.size()}, InstrumentType::kObservableCounter,
       InstrumentValueType::kLong};
   RegisterAsyncMetricStorage<long>(instrument_descriptor, callback);
 }
@@ -76,7 +76,7 @@ void Meter::CreateDoubleObservableCounter(nostd::string_view name,
 {
   InstrumentDescriptor instrument_descriptor = {
       std::string{name.data(), name.size()}, std::string{description.data(), description.size()},
-      std::string{unit.data(), unit.size()}, InstrumentType::kObservableGauge,
+      std::string{unit.data(), unit.size()}, InstrumentType::kObservableCounter,
       InstrumentValueType::kDouble};
   RegisterAsyncMetricStorage<double>(instrument_descriptor, callback);
 }

From e365432644bc1a31b10a8ce11f38a86aacc9c96d Mon Sep 17 00:00:00 2001
From: Lalit <labhas@microsoft.com>
Date: Tue, 10 May 2022 21:53:59 -0700
Subject: [PATCH 5/5] fix format

---
 sdk/include/opentelemetry/sdk/metrics/meter.h | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/sdk/include/opentelemetry/sdk/metrics/meter.h b/sdk/include/opentelemetry/sdk/metrics/meter.h
index d9b2825d13..9d9595f660 100644
--- a/sdk/include/opentelemetry/sdk/metrics/meter.h
+++ b/sdk/include/opentelemetry/sdk/metrics/meter.h
@@ -51,7 +51,7 @@ class Meter final : public opentelemetry::metrics::Meter
       nostd::string_view name,
       void (*callback)(opentelemetry::metrics::ObserverResult<double> &),
       nostd::string_view description = "",
-      nostd::string_view unit        = "1") noexcept override;
+      nostd::string_view unit        = "") noexcept override;
 
   nostd::shared_ptr<opentelemetry::metrics::Histogram<long>> CreateLongHistogram(
       nostd::string_view name,
@@ -119,12 +119,10 @@ class Meter final : public opentelemetry::metrics::Meter
   void RegisterAsyncMetricStorage(InstrumentDescriptor &instrument_descriptor,
                                   void (*callback)(opentelemetry::metrics::ObserverResult<T> &))
   {
-    std::cout << "---LALIT--Register async\n";
     auto view_registry = meter_context_->GetViewRegistry();
     auto success       = view_registry->FindViews(
         instrument_descriptor, *instrumentation_library_,
         [this, &instrument_descriptor, callback](const View &view) {
-          std::cout << "--LALIT  Found view\n";
           auto view_instr_desc         = instrument_descriptor;
           view_instr_desc.name_        = view.GetName();
           view_instr_desc.description_ = view.GetDescription();