Wait for lambdas before stopping loop task

src/platform/tests/TestPlatformMgr.cpp

@@ -23,7 +23,9 @@
  */
 
 #include <atomic>
+#include <condition_variable>
 #include <inttypes.h>
+#include <mutex>
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -42,6 +44,38 @@ using namespace chip::Logging;
 using namespace chip::Inet;
 using namespace chip::DeviceLayer;
 
+namespace {
+
+/**
+ * @brief Simple barrier implementation.
+ * We can use C++20 std::barrier once we support it.
+ */
+class Barrier
+{
+public:
+    explicit Barrier(size_t count) : mCount(count) {}
+
+    void arrive()
+    {
+        std::unique_lock<std::mutex> lock(mMutex);
+        mCount--;
+        mCond.notify_all();
+    }
+
+    void wait()
+    {
+        std::unique_lock<std::mutex> lock(mMutex);
+        mCond.wait(lock, [this] { return mCount == 0; });
+    }
+
+private:
+    std::mutex mMutex;
+    std::condition_variable mCond;
+    size_t mCount;
+};
+
+} // namespace
+
 // =================================
 //      Unit tests
 // =================================
@@ -67,12 +101,22 @@ static void TestPlatformMgr_BasicEventLoopTask(nlTestSuite * inSuite, void * inC
         err = PlatformMgr().StartEventLoopTask();
         NL_TEST_ASSERT(inSuite, err == CHIP_NO_ERROR);
 
+        Barrier sync(2);
+
         // Verify that the event loop will not exit until we tell it to by
         // scheduling few lambdas (for the test to pass, the event loop will
         // have to process more than one event).
-        DeviceLayer::SystemLayer().ScheduleLambda([&counterRun]() { counterRun++; });
+        DeviceLayer::SystemLayer().ScheduleLambda([&]() {
+            counterRun++;
+            sync.arrive();
+        });
         chip::test_utils::SleepMillis(10);
-        DeviceLayer::SystemLayer().ScheduleLambda([&counterRun]() { counterRun++; });
+        DeviceLayer::SystemLayer().ScheduleLambda([&]() {
+            counterRun++;
+            sync.arrive();
+        });
+
+        sync.wait();
 
         err = PlatformMgr().StopEventLoopTask();
         NL_TEST_ASSERT(inSuite, err == CHIP_NO_ERROR);