Fix header only api singletons (#1520)

CHANGELOG.md

@@ -19,6 +19,7 @@ Increment the:
 * [METRICS EXPORTER] Add `OtlpGrpcMetricExporterFactory` and `OtlpHttpMetricExporterFactory`.
   [#1606](https://github.com/open-telemetry/opentelemetry-cpp/pull/1606)
 * [METRICS EXPORTER] Add `OtlpGrpcClient` [#1606](https://github.com/open-telemetry/opentelemetry-cpp/pull/1606)
+* [BUILD] Fix header only api singletons [#1604](https://github.com/open-telemetry/opentelemetry-cpp/pull/1604)
 
 ## [1.6.0] 2022-08-15
 

api/include/opentelemetry/_metrics/provider.h

@@ -7,6 +7,7 @@
 
 #  include "opentelemetry/_metrics/meter_provider.h"
 #  include "opentelemetry/_metrics/noop.h"
+#  include "opentelemetry/common/macros.h"
 #  include "opentelemetry/common/spin_lock_mutex.h"
 #  include "opentelemetry/nostd/shared_ptr.h"
 
@@ -41,13 +42,13 @@ class Provider
   }
 
 private:
-  static nostd::shared_ptr<MeterProvider> &GetProvider() noexcept
+  OPENTELEMETRY_API_SINGLETON static nostd::shared_ptr<MeterProvider> &GetProvider() noexcept
   {
     static nostd::shared_ptr<MeterProvider> provider(new NoopMeterProvider);
     return provider;
   }
 
-  static common::SpinLockMutex &GetLock() noexcept
+  OPENTELEMETRY_API_SINGLETON static common::SpinLockMutex &GetLock() noexcept
   {
     static common::SpinLockMutex lock;
     return lock;

api/include/opentelemetry/baggage/baggage.h

@@ -6,6 +6,7 @@
 #include <cctype>
 
 #include "opentelemetry/common/kv_properties.h"
+#include "opentelemetry/common/macros.h"
 #include "opentelemetry/nostd/shared_ptr.h"
 #include "opentelemetry/nostd/string_view.h"
 #include "opentelemetry/version.h"
@@ -34,7 +35,7 @@ class Baggage
       : kv_properties_(new opentelemetry::common::KeyValueProperties(keys_and_values))
   {}
 
-  static nostd::shared_ptr<Baggage> GetDefault()
+  OPENTELEMETRY_API_SINGLETON static nostd::shared_ptr<Baggage> GetDefault()
   {
     static nostd::shared_ptr<Baggage> baggage{new Baggage()};
     return baggage;

api/include/opentelemetry/common/macros.h

@@ -89,3 +89,86 @@
 #else
 #  define OPENTELEMETRY_DEPRECATED_MESSAGE(msg)
 #endif
+
+/* clang-format off */
+
+/**
+  @page HEADER_ONLY_SINGLETON Header only singleton.
+
+  @section ELF_SINGLETON
+
+  For clang and gcc, the desired coding pattern is as follows.
+
+  @verbatim
+  class Foo
+  {
+    // (a)
+    __attribute__((visibility("default")))
+    // (b)
+    T& get_singleton()
+    {
+      // (c)
+      static T singleton;
+      return singleton;
+    }
+  };
+  @endverbatim
+
+  (a) is needed when the code is build with
+  @code -fvisibility="hidden" @endcode
+  to ensure that all instances of (b) are visible to the linker.
+
+  What is duplicated in the binary is @em code, in (b).
+
+  The linker will make sure only one instance
+  of all the (b) methods is used.
+
+  (c) is a singleton implemented inside a method.
+
+  This is very desirable, because:
+
+  - the C++ compiler guarantees that construction
+    of the variable (c) is thread safe.
+
+  - constructors for (c) singletons are executed in code path order,
+    or not at all if the singleton is never used.
+
+  @section OTHER_SINGLETON
+
+  For other platforms, header only singletons are not supported at this
+point.
+
+  @section CODING_PATTERN
+
+  The coding pattern to use in the source code is as follows
+
+  @verbatim
+  class Foo
+  {
+    OPENTELEMETRY_API_SINGLETON
+    T& get_singleton()
+    {
+      static T singleton;
+      return singleton;
+    }
+  };
+  @endverbatim
+*/
+
+/* clang-format on */
+
+#if defined(__clang__)
+
+#  define OPENTELEMETRY_API_SINGLETON __attribute__((visibility("default")))
+
+#elif defined(__GNUC__)
+
+#  define OPENTELEMETRY_API_SINGLETON __attribute__((visibility("default")))
+
+#else
+
+/* Add support for other compilers here. */
+
+#  define OPENTELEMETRY_API_SINGLETON
+
+#endif

api/include/opentelemetry/context/propagation/global_propagator.h

@@ -8,6 +8,7 @@
 #include "opentelemetry/context/propagation/noop_propagator.h"
 #include "opentelemetry/context/propagation/text_map_propagator.h"
 
+#include "opentelemetry/common/macros.h"
 #include "opentelemetry/common/spin_lock_mutex.h"
 #include "opentelemetry/nostd/shared_ptr.h"
 
@@ -37,13 +38,13 @@ class GlobalTextMapPropagator
   }
 
 private:
-  static nostd::shared_ptr<TextMapPropagator> &GetPropagator() noexcept
+  OPENTELEMETRY_API_SINGLETON static nostd::shared_ptr<TextMapPropagator> &GetPropagator() noexcept
   {
     static nostd::shared_ptr<TextMapPropagator> propagator(new NoOpPropagator());
     return propagator;
   }
 
-  static common::SpinLockMutex &GetLock() noexcept
+  OPENTELEMETRY_API_SINGLETON static common::SpinLockMutex &GetLock() noexcept
   {
     static common::SpinLockMutex lock;
     return lock;
@@ -52,4 +53,4 @@ class GlobalTextMapPropagator
 
 }  // namespace propagation
 }  // namespace context
-OPENTELEMETRY_END_NAMESPACE
+OPENTELEMETRY_END_NAMESPACE

api/include/opentelemetry/context/runtime_context.h

@@ -3,6 +3,7 @@
 
 #pragma once
 
+#include "opentelemetry/common/macros.h"
 #include "opentelemetry/context/context.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
@@ -166,7 +167,7 @@ class RuntimeContext
     return GetStorage();
   }
 
-  static nostd::shared_ptr<RuntimeContextStorage> &GetStorage() noexcept
+  OPENTELEMETRY_API_SINGLETON static nostd::shared_ptr<RuntimeContextStorage> &GetStorage() noexcept
   {
     static nostd::shared_ptr<RuntimeContextStorage> context(GetDefaultStorage());
     return context;
@@ -315,7 +316,7 @@ class ThreadLocalContextStorage : public RuntimeContextStorage
     Context *base_;
   };
 
-  Stack &GetStack()
+  OPENTELEMETRY_API_SINGLETON Stack &GetStack()
   {
     static thread_local Stack stack_ = Stack();
     return stack_;

api/include/opentelemetry/logs/provider.h

@@ -6,6 +6,7 @@
 
 #  include <mutex>
 
+#  include "opentelemetry/common/macros.h"
 #  include "opentelemetry/common/spin_lock_mutex.h"
 #  include "opentelemetry/logs/logger_provider.h"
 #  include "opentelemetry/logs/noop.h"
@@ -42,13 +43,13 @@ class Provider
   }
 
 private:
-  static nostd::shared_ptr<LoggerProvider> &GetProvider() noexcept
+  OPENTELEMETRY_API_SINGLETON static nostd::shared_ptr<LoggerProvider> &GetProvider() noexcept
   {
     static nostd::shared_ptr<LoggerProvider> provider(new NoopLoggerProvider);
     return provider;
   }
 
-  static common::SpinLockMutex &GetLock() noexcept
+  OPENTELEMETRY_API_SINGLETON static common::SpinLockMutex &GetLock() noexcept
   {
     static common::SpinLockMutex lock;
     return lock;

api/include/opentelemetry/metrics/provider.h

@@ -6,6 +6,7 @@
 
 #  include <mutex>
 
+#  include "opentelemetry/common/macros.h"
 #  include "opentelemetry/common/spin_lock_mutex.h"
 #  include "opentelemetry/metrics/meter_provider.h"
 #  include "opentelemetry/metrics/noop.h"
@@ -42,13 +43,13 @@ class Provider
   }
 
 private:
-  static nostd::shared_ptr<MeterProvider> &GetProvider() noexcept
+  OPENTELEMETRY_API_SINGLETON static nostd::shared_ptr<MeterProvider> &GetProvider() noexcept
   {
     static nostd::shared_ptr<MeterProvider> provider(new NoopMeterProvider);
     return provider;
   }
 
-  static common::SpinLockMutex &GetLock() noexcept
+  OPENTELEMETRY_API_SINGLETON static common::SpinLockMutex &GetLock() noexcept
   {
     static common::SpinLockMutex lock;
     return lock;
@@ -57,4 +58,4 @@ class Provider
 
 }  // namespace metrics
 OPENTELEMETRY_END_NAMESPACE
-#endif
+#endif

api/include/opentelemetry/trace/provider.h

@@ -5,6 +5,7 @@
 
 #include <mutex>
 
+#include "opentelemetry/common/macros.h"
 #include "opentelemetry/common/spin_lock_mutex.h"
 #include "opentelemetry/nostd/shared_ptr.h"
 #include "opentelemetry/trace/noop.h"
@@ -41,13 +42,13 @@ class Provider
   }
 
 private:
-  static nostd::shared_ptr<TracerProvider> &GetProvider() noexcept
+  OPENTELEMETRY_API_SINGLETON static nostd::shared_ptr<TracerProvider> &GetProvider() noexcept
   {
     static nostd::shared_ptr<TracerProvider> provider(new NoopTracerProvider);
     return provider;
   }
 
-  static common::SpinLockMutex &GetLock() noexcept
+  OPENTELEMETRY_API_SINGLETON static common::SpinLockMutex &GetLock() noexcept
   {
     static common::SpinLockMutex lock;
     return lock;

api/include/opentelemetry/trace/trace_state.h

@@ -15,6 +15,7 @@
 #endif
 
 #include "opentelemetry/common/kv_properties.h"
+#include "opentelemetry/common/macros.h"
 #include "opentelemetry/nostd/shared_ptr.h"
 #include "opentelemetry/nostd/span.h"
 #include "opentelemetry/nostd/string_view.h"
@@ -41,7 +42,7 @@ class TraceState
   static constexpr auto kKeyValueSeparator = '=';
   static constexpr auto kMembersSeparator  = ',';
 
-  static nostd::shared_ptr<TraceState> GetDefault()
+  OPENTELEMETRY_API_SINGLETON static nostd::shared_ptr<TraceState> GetDefault()
   {
     static nostd::shared_ptr<TraceState> ts{new TraceState()};
     return ts;
@@ -316,5 +317,6 @@ class TraceState
   // Store entries in a C-style array to avoid using std::array or std::vector.
   nostd::unique_ptr<opentelemetry::common::KeyValueProperties> kv_properties_;
 };
+
 }  // namespace trace
 OPENTELEMETRY_END_NAMESPACE

api/test/CMakeLists.txt

@@ -13,3 +13,4 @@ if(WITH_LOGS_PREVIEW)
 endif()
 add_subdirectory(common)
 add_subdirectory(baggage)
+add_subdirectory(singleton)