[WIP] Synchronous Gauge

api/include/opentelemetry/metrics/meter.h

@@ -21,6 +21,9 @@ class Histogram;
 template <typename T>
 class UpDownCounter;
 
+template <typename T>
+class Gauge;
+
 class ObservableInstrument;
 
 /**
@@ -91,6 +94,27 @@ class Meter
       nostd::string_view description = "",
       nostd::string_view unit        = "") noexcept = 0;
 
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  /**
+   * Creates a Gauge with the passed characteristics and returns a
+   * unique_ptr to that Gauge
+   *  @since ABI_VERSION 2
+   *
+   * @param name the name of the new Gauge.
+   * @param description a brief description of what the Gauge is used for.
+   * @param unit the unit of metric values following https://unitsofmeasure.org/ucum.html.
+   */
+  virtual nostd::unique_ptr<Gauge<uint64_t>> CreateInt64Gauge(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept = 0;
+
+  virtual nostd::unique_ptr<Gauge<double>> CreateDoubleGauge(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept = 0;
+#endif
+
   /**
    * Creates a Asynchronouse (Observable) Gauge with the passed characteristics and returns a
    * shared_ptr to that Observable Gauge

api/include/opentelemetry/metrics/noop.h

@@ -44,6 +44,13 @@ class NoopHistogram : public Histogram<T>
               const common::KeyValueIterable & /* attributes */,
               const context::Context & /* context */) noexcept override
   {}
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  void Record(T /*value*/,
+              const opentelemetry::common::KeyValueIterable & /*attributes*/) noexcept override
+  {}
+
+  void Record(T /*value*/) noexcept override {}
+#endif
 };
 
 template <class T>
@@ -64,6 +71,23 @@ class NoopUpDownCounter : public UpDownCounter<T>
   {}
 };
 
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+
+template <class T>
+class NoopGauge : public Gauge<T>
+{
+public:
+  NoopGauge(nostd::string_view /* name */,
+            nostd::string_view /* description */,
+            nostd::string_view /* unit */) noexcept
+  {}
+  void Record(T /* value */,
+              const common::KeyValueIterable * /* attributes */,
+              const context::Context * /* context */) noexcept override
+  {}
+};
+#endif
+
 class NoopObservableInstrument : public ObservableInstrument
 {
 public:
@@ -133,6 +157,25 @@ class NoopMeter final : public Meter
     return nostd::unique_ptr<Histogram<double>>{new NoopHistogram<double>(name, description, unit)};
   }
 
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+
+  nostd::unique_ptr<Gauge<uint64_t>> CreateInt64Gauge(
+      nostd::string_view name,
+      nostd::string_view description = "",
+      nostd::string_view unit        = "") noexcept override
+  {
+    return nostd::unique_ptr<Gauge<uint64_t>>(new NoopGauge<uint64_t>(name, description, unit));
+  }
+
+  nostd::unique_ptr<Gauge<double>> CreateDoubleGauge(nostd::string_view name,
+                                                     nostd::string_view description = "",
+                                                     nostd::string_view unit = "") noexcept override
+  {
+    return nostd::unique_ptr<Gauge<double>>(new NoopGauge<double>(name, description, unit));
+  }
+
+#endif
+
   nostd::shared_ptr<ObservableInstrument> CreateInt64ObservableGauge(
       nostd::string_view name,
       nostd::string_view description = "",