[fluentd] Add force_flush to fluentd exporters (open-telemetry#522)

Author: ThomsonTan

exporters/fluentd/CMakeLists.txt

@@ -133,16 +133,22 @@ if(OPENTELEMETRY_INSTALL)
 endif()
 
 if(BUILD_TESTING)
-  include(GoogleTest)
+  if(MAIN_PROJECT)
+    find_package(GTest CONFIG REQUIRED)
+  else()
+    if (NOT DEFINED GTEST_BOTH_LIBRARIES)
+      message(STATUS_FATAL, "Test is not enable.")
+    endif()
+  endif()
+  # include(GoogleTest)
   # build trace exporter tests
   add_executable(
     fluentd_recordable_trace_test test/trace/fluentd_recordable_test.cc
                                   test/trace/fluentd_baseline_test.cc)
 
   target_link_libraries(
     fluentd_recordable_trace_test
-    gtest
-    gtest_main
+    ${GTEST_BOTH_LIBRARIES}
     ${CMAKE_THREAD_LIBS_INIT}
     opentelemetry_common
     opentelemetry_trace
@@ -164,8 +170,7 @@ if(BUILD_TESTING)
 
   target_link_libraries(
     fluentd_recordable_logs_test
-    gtest
-    gtest_main
+    ${GTEST_BOTH_LIBRARIES}
     ${CMAKE_THREAD_LIBS_INIT}
     opentelemetry_common
     opentelemetry_logs

exporters/fluentd/include/opentelemetry/exporters/fluentd/log/fluentd_exporter.h

@@ -50,6 +50,12 @@ class FluentdExporter final : public logs_sdk::LogRecordExporter {
   Export(const nostd::span<std::unique_ptr<logs_sdk::Recordable>>
              &logs) noexcept override;
 
+  bool ForceFlush(
+      std::chrono::microseconds timeout = (std::chrono::microseconds::max)()) noexcept override
+  {
+        return true;
+  }
+
   /**
    * Shut down the exporter.
    * @param timeout an optional timeout, default to max.

exporters/fluentd/include/opentelemetry/exporters/fluentd/trace/fluentd_exporter.h

@@ -55,6 +55,12 @@ class FluentdExporter final : public trace_sdk::SpanExporter {
   Export(const nostd::span<std::unique_ptr<trace_sdk::Recordable>>
              &spans) noexcept override;
 
+  bool ForceFlush(
+      std::chrono::microseconds timeout = (std::chrono::microseconds::max)()) noexcept override
+  {
+        return true;
+  }
+
   /**
    * Shut down the exporter.
    * @param timeout an optional timeout, default to max.