pass an out pointer to capture function return result

Author: Alami-Amine

src/lib/support/LambdaBridge.h

@@ -28,47 +28,41 @@ class LambdaBridge
 public:
     // Use initialize instead of constructor because this class has to be trivial
     template <typename Lambda>
-    void Initialize(const Lambda & lambda)
+    void Initialize(const Lambda & lambda, CHIP_ERROR * Error_Value = nullptr)
     {
+        // LambdaBridge accepts either Lambdas without arguments or those with `CHIP_ERROR *` as argument.
+        mpError = Error_Value;
+
         // memcpy is used to move the lambda into the event queue, so it must be trivially copyable
         static_assert(std::is_trivially_copyable<Lambda>::value, "lambda must be trivially copyable");
         static_assert(sizeof(Lambda) <= CHIP_CONFIG_LAMBDA_EVENT_SIZE, "lambda too large");
         static_assert(CHIP_CONFIG_LAMBDA_EVENT_ALIGN % alignof(Lambda) == 0, "lambda align too large");
 
         // Implicit cast a capture-less lambda into a raw function pointer.
-        if constexpr (std::is_same_v<decltype(lambda()), void>)
-        {
-            mLambdaVoidProxy = [](const LambdaStorage & body) { (*reinterpret_cast<const Lambda *>(&body))(); };
-        }
-        else if constexpr (std::is_same_v<decltype(lambda()), CHIP_ERROR>)
-        {
-            mLambdaProxy = [](const LambdaStorage & body) { return (*reinterpret_cast<const Lambda *>(&body))(); };
-        }
+        mLambdaProxy = [](const LambdaStorage & body, CHIP_ERROR * apError) {
+            // Check if lambda has CHIP_ERROR * as argument, if not, call it without arguments
+            if constexpr (std::is_invocable<Lambda, CHIP_ERROR *>::value)
+            {
+                // Call the lambda with CHIP_ERROR* argument
+                (*reinterpret_cast<const Lambda *>(&body))(apError);
+            }
+            else
+            {
+                // Call the lambda with no arguments
+                (*reinterpret_cast<const Lambda *>(&body))();
+            }
+        };
 
         ::memcpy(&mLambdaBody, &lambda, sizeof(Lambda));
     }
 
-    void operator()() const
-    {
-        if (mLambdaVoidProxy != nullptr)
-        {
-            mLambdaVoidProxy(mLambdaBody);
-        }
-    }
-    CHIP_ERROR CallLambdaWithErrorReturn() const
-    {
-        if (mLambdaProxy != nullptr)
-        {
-            return mLambdaProxy(mLambdaBody);
-        }
-        return CHIP_ERROR_INTERNAL; // Return an error if the proxy is not for CHIP_ERROR
-    }
+    void operator()() const { mLambdaProxy(mLambdaBody, mpError); }
 
 private:
     using LambdaStorage = std::aligned_storage_t<CHIP_CONFIG_LAMBDA_EVENT_SIZE, CHIP_CONFIG_LAMBDA_EVENT_ALIGN>;
-    void (*mLambdaVoidProxy)(const LambdaStorage & body);
-    CHIP_ERROR (*mLambdaProxy)(const LambdaStorage & body);
+    void (*mLambdaProxy)(const LambdaStorage & body, CHIP_ERROR * mpError);
     LambdaStorage mLambdaBody;
+    CHIP_ERROR * mpError;
 };
 
 static_assert(std::is_trivial<LambdaBridge>::value, "LambdaBridge is not trivial");

src/platform/Linux/PlatformManagerImpl.cpp

@@ -281,7 +281,7 @@ void PlatformManagerImpl::_Shutdown()
 }
 
 #if CHIP_DEVICE_CONFIG_WITH_GLIB_MAIN_LOOP
-CHIP_ERROR PlatformManagerImpl::_GLibMatterContextInvokeSync(LambdaBridge && bridge)
+void PlatformManagerImpl::_GLibMatterContextInvokeSync(LambdaBridge && bridge)
 {
     // Because of TSAN false positives, we need to use a mutex to synchronize access to all members of
     // the GLibMatterContextInvokeData object (including constructor and destructor). This is a temporary
@@ -301,22 +301,18 @@ CHIP_ERROR PlatformManagerImpl::_GLibMatterContextInvokeSync(LambdaBridge && bri
             std::unique_lock<std::mutex> lock_(PlatformMgrImpl().mGLibMainLoopCallbackIndirectionMutex);
 
             lock_.unlock();
-            auto result = data->bridge.CallLambdaWithErrorReturn();
+            data->bridge();
             lock_.lock();
 
-            data->mDone       = true;
-            data->mFuncResult = result;
+            data->mDone = true;
             data->mDoneCond.notify_one();
 
             return G_SOURCE_REMOVE;
         },
         &invokeData, nullptr);
 
     lock.lock();
-
     invokeData.mDoneCond.wait(lock, [&invokeData]() { return invokeData.mDone; });
-
-    return invokeData.mFuncResult;
 }
 #endif // CHIP_DEVICE_CONFIG_WITH_GLIB_MAIN_LOOP
 

src/platform/Linux/PlatformManagerImpl.h

@@ -69,11 +69,16 @@ class PlatformManagerImpl final : public PlatformManager, public Internal::Gener
     template <typename T>
     CHIP_ERROR GLibMatterContextInvokeSync(CHIP_ERROR (*func)(T *), T * userData)
     {
-        auto lambda = [func, userData]() -> CHIP_ERROR { return func(userData); };
+        CHIP_ERROR LambdaErrorReturn;
+        
+        // wrapping the function pointer and userData into a Lambda, to be stored and passed as a LambdaBridge
+        auto lambda = [func, userData](CHIP_ERROR * apErrorReturn) { *apErrorReturn = func(userData); };
 
         LambdaBridge bridge;
-        bridge.Initialize(lambda);
-        return _GLibMatterContextInvokeSync(std::move(bridge));
+        bridge.Initialize(lambda, &LambdaErrorReturn);
+        _GLibMatterContextInvokeSync(std::move(bridge));
+
+        return LambdaErrorReturn;
     }
 
     unsigned int GLibMatterContextAttachSource(GSource * source)
@@ -107,7 +112,6 @@ class PlatformManagerImpl final : public PlatformManager, public Internal::Gener
     struct GLibMatterContextInvokeData
     {
         LambdaBridge bridge;
-        CHIP_ERROR mFuncResult;
         // Sync primitives to wait for the function to be executed
         std::condition_variable mDoneCond;
         bool mDone = false;
@@ -116,10 +120,13 @@ class PlatformManagerImpl final : public PlatformManager, public Internal::Gener
     /**
      * @brief Invoke a function on the Matter GLib context.
      *
-     * @note This function does not provide type safety for the user data. Please,
-     *       use the GLibMatterContextInvokeSync() template function instead.
+     * @param[in] bridge a LambdaBridge object that holds the lambda to be invoked within the GLib context.
+     *
+     * @note This function moves the LambdaBridge into the GLib context for invocation.
+     *       The LambdaBridge is created and initialised in GLibMatterContextInvokeSync().
+     *       use the GLibMatterContextInvokeSync() template function instead of this one.
      */
-    CHIP_ERROR _GLibMatterContextInvokeSync(LambdaBridge && bridge);
+    void _GLibMatterContextInvokeSync(LambdaBridge && bridge);
 
     // XXX: Mutex for guarding access to glib main event loop callback indirection
     //      synchronization primitives. This is a workaround to suppress TSAN warnings.