Fix AtomicSharedPtr for C++20

.github/workflows/ci.yml

@@ -19,6 +19,18 @@ jobs:
     - name: run tests
       run: ./ci/do_ci.sh cmake.test
 
+  cmake_test_cxx20:
+    name: CMake C++20 test
+    runs-on: ubuntu-20.04
+    steps:
+    - uses: actions/checkout@v2
+    - name: setup
+      run: |
+        sudo ./ci/setup_ci_environment.sh
+        sudo ./ci/setup_cmake.sh
+    - name: run tests
+      run: ./ci/do_ci.sh cmake.c++20.test
+
   plugin_test:
     name: Plugin -> CMake
     runs-on: ubuntu-latest

CMakeLists.txt

@@ -6,7 +6,9 @@ cmake_policy(SET CMP0057 NEW)
 
 project(opentelemetry-cpp)
 
-set(CMAKE_CXX_STANDARD 11)
+if(NOT DEFINED CMAKE_CXX_STANDARD)
+  set(CMAKE_CXX_STANDARD 11)
+endif()
 
 option(WITH_OTPROTOCOL
        "Whether to include the OpenTelemetry Protocol in the SDK" OFF)

ci/do_ci.sh

@@ -20,6 +20,16 @@ if [[ "$1" == "cmake.test" ]]; then
   make
   make test
   exit 0
+elif [[ "$1" == "cmake.c++20.test" ]]; then
+  cd "${BUILD_DIR}"
+  rm -rf *
+  cmake -DCMAKE_BUILD_TYPE=Debug  \
+        -DCMAKE_CXX_FLAGS="-Werror" \
+        -DCMAKE_CXX_STANDARD=20 \
+        "${SRC_DIR}"
+  make
+  make test
+  exit 0
 elif [[ "$1" == "cmake.exporter.otprotocol.test" ]]; then
   cd "${BUILD_DIR}"
   rm -rf *

ci/setup_cmake.sh

@@ -12,5 +12,5 @@ apt-get install --no-install-recommends --no-install-suggests -y \
 pushd /usr/src/gtest
 cmake CMakeLists.txt
 make
-cp *.a /usr/lib
+cp *.a /usr/lib || cp lib/*.a /usr/lib
 popd

sdk/include/opentelemetry/sdk/common/atomic_shared_ptr.h

@@ -11,28 +11,10 @@ namespace sdk
 /**
  * A wrapper to provide atomic shared pointers.
  *
- * This wrapper relies on std::atomic for C++20, a mutex for gcc 4.8, and
- * specializations of std::atomic_store and std::atomic_load for all other
- * instances.
+ * This wrapper relies on a mutex for gcc 4.8, and specializations of
+ * std::atomic_store and std::atomic_load for all other instances.
  */
-#if __cplusplus > 201703L
-template <class T>
-class AtomicSharedPtr
-{
-public:
-  explicit AtomicSharedPtr(std::shared_ptr<T> ptr) noexcept : ptr_{std::move(ptr)} {}
-
-  void store(const std::shared_ptr<T> &other) noexcept
-  {
-    ptr_.store(other, std::memory_order_release);
-  }
-
-  std::shared_ptr<T> load() const noexcept { return ptr_.load(std::memory_order_acquire); }
-
-private:
-  std::atomic<std::shared_ptr<T>> ptr_;
-};
-#elif (__GNUC__ == 4 && (__GNUC_MINOR__ >= 8))
+#if (__GNUC__ == 4 && (__GNUC_MINOR__ >= 8))
 template <class T>
 class AtomicSharedPtr
 {