[API] Add Enabled method to Tracer

CHANGELOG.md

@@ -21,6 +21,9 @@ Increment the:
 * [CMAKE] Bump cmake minimum required version to 3.14
   [#3349](https://github.com/open-telemetry/opentelemetry-cpp/pull/3349)
 
+* [API] Add Enabled method to Tracer
+  [#3357](https://github.com/open-telemetry/opentelemetry-cpp/pull/3357)
+
 ## [1.20 2025-04-01]
 
 * [BUILD] Update opentelemetry-proto version

api/include/opentelemetry/plugin/tracer.h

@@ -104,6 +104,10 @@ class Tracer final : public trace::Tracer, public std::enable_shared_from_this<T
     return nostd::shared_ptr<trace::Span>{new (std::nothrow) Span{this->shared_from_this(), span}};
   }
 
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  bool Enabled() const noexcept override { return true; }
+#endif
+
 #if OPENTELEMETRY_ABI_VERSION_NO == 1
 
   void ForceFlushWithMicroseconds(uint64_t timeout) noexcept override

api/include/opentelemetry/trace/noop.h

@@ -108,6 +108,10 @@ class OPENTELEMETRY_EXPORT NoopTracer final : public Tracer,
     return noop_span;
   }
 
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  bool Enabled() const noexcept override { return false; }
+#endif
+
 #if OPENTELEMETRY_ABI_VERSION_NO == 1
 
   void ForceFlushWithMicroseconds(uint64_t /*timeout*/) noexcept override {}

api/include/opentelemetry/trace/tracer.h

@@ -163,6 +163,18 @@ class Tracer
     }
   }
 
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  /**
+   * Reports if the tracer is enabled or not. A disabled tracer will not create spans.
+   *
+   * The instrumentation authors should call this method before creating a spans to
+   * potentially avoid performing computationally expensive operations for disabled tracers.
+   *
+   * @since ABI_VERSION 2
+   */
+  virtual bool Enabled() const noexcept = 0;
+#endif
+
 #if OPENTELEMETRY_ABI_VERSION_NO == 1
 
   /*

api/test/singleton/singleton_test.cc

@@ -285,6 +285,12 @@ class MyTracer : public trace::Tracer
     return result;
   }
 
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+
+  bool Enabled() const noexcept override { return true; }
+
+#endif
+
 #if OPENTELEMETRY_ABI_VERSION_NO == 1
 
   void ForceFlushWithMicroseconds(uint64_t /* timeout */) noexcept override {}

api/test/trace/noop_test.cc

@@ -70,6 +70,8 @@ TEST(NoopTest, UseNoopTracersAbiv2)
   s1->AddLink(target, {{"noop1", 1}});
 
   s1->AddLinks({{trace_api::SpanContext(false, false), {{"noop2", 2}}}});
+
+  EXPECT_FALSE(tracer->Enabled());
 }
 #endif /* OPENTELEMETRY_ABI_VERSION_NO >= 2 */
 

examples/plugin/plugin/tracer.cc

@@ -91,3 +91,10 @@ nostd::shared_ptr<trace::Span> Tracer::StartSpan(nostd::string_view name,
   return nostd::shared_ptr<trace::Span>{
       new (std::nothrow) Span{this->shared_from_this(), name, attributes, links, options}};
 }
+
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+bool Tracer::Enabled() const noexcept
+{
+  return true;
+}
+#endif

examples/plugin/plugin/tracer.h

@@ -26,6 +26,12 @@ class Tracer final : public opentelemetry::trace::Tracer,
       const opentelemetry::trace::SpanContextKeyValueIterable & /*links*/,
       const opentelemetry::trace::StartSpanOptions & /*options */) noexcept override;
 
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+
+  bool Enabled() const noexcept override;
+
+#endif
+
 #if OPENTELEMETRY_ABI_VERSION_NO == 1
 
   void ForceFlushWithMicroseconds(uint64_t /*timeout*/) noexcept override {}

exporters/etw/include/opentelemetry/exporters/etw/etw_tracer.h

@@ -590,6 +590,20 @@ class Tracer : public opentelemetry::trace::Tracer,
     return result;
   }
 
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  /**
+   * Reports if the tracer is enabled or not. A disabled tracer will not create spans.
+   * Note: The etw_tracer currently does not accept a TracerConfig and can therefore not be disabled
+   * based on the instrumentation scope.
+   *
+   * The instrumentation authors should call this method before creating a spans to
+   * potentially avoid performing computationally expensive operations for disabled tracers.
+   *
+   * @since ABI_VERSION 2
+   */
+  virtual bool Enabled() const noexcept { return true; }
+#endif
+
 #if OPENTELEMETRY_ABI_VERSION_NO == 1
   /**
    * @brief Force flush data to Tracer, spending up to given amount of microseconds to flush.

sdk/include/opentelemetry/sdk/trace/tracer.h

@@ -71,6 +71,8 @@ class Tracer final : public opentelemetry::trace::Tracer,
   }
 
   void CloseWithMicroseconds(uint64_t timeout) noexcept;
+
+  bool Enabled() const noexcept override;
 #else
   /* Exposed in the API in ABI version 1, but does not belong to the API */
   void ForceFlushWithMicroseconds(uint64_t timeout) noexcept override;

sdk/src/trace/tracer.cc

@@ -163,6 +163,13 @@ nostd::shared_ptr<opentelemetry::trace::Span> Tracer::StartSpan(
   }
 }
 
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+bool Tracer::Enabled() const noexcept
+{
+  return tracer_config_.IsEnabled();
+}
+#endif
+
 void Tracer::ForceFlushWithMicroseconds(uint64_t timeout) noexcept
 {
   if (context_)

sdk/test/trace/tracer_test.cc

@@ -508,6 +508,11 @@ TEST(Tracer, StartSpanWithDisabledConfig)
       std::make_shared<opentelemetry::trace::NoopTracer>();
   auto noop_span = noop_tracer->StartSpan("noop");
   EXPECT_TRUE(span.get() == noop_span.get());
+
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  EXPECT_FALSE(noop_tracer->Enabled());
+  EXPECT_FALSE(tracer->Enabled());
+#endif
 }
 
 TEST(Tracer, StartSpanWithEnabledConfig)
@@ -524,6 +529,11 @@ TEST(Tracer, StartSpanWithEnabledConfig)
       std::make_shared<opentelemetry::trace::NoopTracer>();
   auto noop_span = noop_tracer->StartSpan("noop");
   EXPECT_FALSE(span.get() == noop_span.get());
+
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  EXPECT_FALSE(noop_tracer->Enabled());
+  EXPECT_TRUE(tracer->Enabled());
+#endif
 }
 
 TEST(Tracer, StartSpanWithCustomConfig)
@@ -567,6 +577,14 @@ TEST(Tracer, StartSpanWithCustomConfig)
                  new RandomIdGenerator(), custom_configurator, std::move(bar_scope));
   auto span_bar_scope = tracer_bar_scope->StartSpan("span 1");
   EXPECT_FALSE(span_bar_scope == noop_span);
+
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  EXPECT_FALSE(noop_tracer->Enabled());
+  EXPECT_FALSE(tracer_default_scope->Enabled());
+  EXPECT_FALSE(tracer_foo_scope->Enabled());
+  EXPECT_TRUE(tracer_foo_scope_with_version->Enabled());
+  EXPECT_TRUE(tracer_bar_scope->Enabled());
+#endif
 }
 
 TEST(Tracer, StartSpanWithCustomConfigDifferingConditionOrder)
@@ -608,6 +626,11 @@ TEST(Tracer, StartSpanWithCustomConfigDifferingConditionOrder)
   // evaluating other condition
   const auto span_foo_scope_with_version_2 = tracer_foo_scope_with_version_2->StartSpan("span 1");
   EXPECT_TRUE(span_foo_scope_with_version_2 == noop_span);
+
+#if OPENTELEMETRY_ABI_VERSION_NO >= 2
+  EXPECT_TRUE(tracer_foo_scope_with_version_1->Enabled());
+  EXPECT_FALSE(tracer_foo_scope_with_version_2->Enabled());
+#endif
 }
 
 TEST(Tracer, SpanSetLinks)