some more little fixes and improvements

src/benchmark/benchmark_ipc_channel.cpp

@@ -25,7 +25,7 @@ TEST_CASE("benchmark_ipc_channel")
 {
 	auto end_a_thread_b_p = make_test_ipc_channel([](IPCChannelEnd end_b) {
 		// echos back messages. stops if "" is sent
-		for (;;) {
+		while (true) {
 			end_b.recv();
 			end_b.send(end_b.getRecvData(), end_b.getRecvSize());
 			if (end_b.getRecvSize() == 0)

src/threading/ipc_channel.cpp

@@ -80,7 +80,7 @@ static bool wait(IPCChannelBuffer *buf, const struct timespec *timeout) noexcept
 		if (buf->futex.load(std::memory_order_acquire) == 1) {
 			// yes
 			// reset it. (relaxed ordering is sufficient, because the other thread
-			// does not need to see the side effects we did before writing 0)
+			// does not need to see the side effects we did before unposting)
 			buf->futex.store(0, std::memory_order_relaxed);
 			return true;
 		}
@@ -93,7 +93,7 @@ static bool wait(IPCChannelBuffer *buf, const struct timespec *timeout) noexcept
 	// wait with futex
 	while (true) {
 		// write 2 to show that we're futexing
-		if (buf->futex.exchange(2, std::memory_order_acq_rel) == 1) {
+		if (buf->futex.exchange(2, std::memory_order_acquire) == 1) {
 			// it was posted in the meantime
 			buf->futex.store(0, std::memory_order_relaxed);
 			return true;
@@ -113,7 +113,7 @@ static bool wait(IPCChannelBuffer *buf, const struct timespec *timeout) noexcept
 
 static void post(IPCChannelBuffer *buf) noexcept
 {
-	if (buf->futex.exchange(1, std::memory_order_acq_rel) == 2) {
+	if (buf->futex.exchange(1, std::memory_order_release) == 2) {
 		// 2 means reader needs to be notified
 		int s = futex(&buf->futex, FUTEX_WAKE, 1, nullptr, nullptr, 0);
 		if (s == -1) {
@@ -130,17 +130,18 @@ static void post(IPCChannelBuffer *buf) noexcept
 // returns false on timeout
 static bool wait(IPCChannelBuffer *buf, const struct timespec *timeout) noexcept
 {
-	bool timed_out = false;
 	pthread_mutex_lock(&buf->mutex);
-	if (!buf->posted) {
-		if (timeout)
-			timed_out = pthread_cond_timedwait(&buf->cond, &buf->mutex, timeout) == ETIMEDOUT;
-		else
+	while (!buf->posted) {
+		if (timeout) {
+			if (pthread_cond_timedwait(&buf->cond, &buf->mutex, timeout) == ETIMEDOUT)
+				return false;
+		} else {
 			pthread_cond_wait(&buf->cond, &buf->mutex);
 		}
+	}
 	buf->posted = false;
 	pthread_mutex_unlock(&buf->mutex);
-	return !timed_out;
+	return true;
 }
 
 static void post(IPCChannelBuffer *buf) noexcept
@@ -172,18 +173,19 @@ static bool wait_in(IPCChannelEnd::Dir *dir, u64 timeout_ms_abs)
 	struct timespec timeout;
 	struct timespec *timeoutp = nullptr;
 	if (timeout_ms_abs > 0) {
-		// Relative time
 		u64 tnow = porting::getTimeMs();
 		if (tnow > timeout_ms_abs)
 			return false;
 		u64 timeout_ms_rel = timeout_ms_abs - tnow;
 #if defined(IPC_CHANNEL_IMPLEMENTATION_LINUX_FUTEX)
+		// Relative time
 		timeout.tv_sec = 0;
 		timeout.tv_nsec = 0;
 #elif defined(IPC_CHANNEL_IMPLEMENTATION_POSIX)
 		// Absolute time, relative to cond_clockid
 		FATAL_ERROR_IF(clock_gettime(dir->buf_in->cond_clockid, &timeout) < 0,
 				"clock_gettime failed");
+		// prevent overflow
 		if (timeout.tv_nsec >= 1000'000'000L) {
 			timeout.tv_nsec -= 1000'000'000L;
 			timeout.tv_sec += 1;
@@ -339,6 +341,7 @@ bool IPCChannelEnd::recvWithTimeout(int timeout_ms) noexcept
 	if (size <= IPC_CHANNEL_MSG_SIZE) {
 		// small msg
 		// (m_large_recv.size() is always >= IPC_CHANNEL_MSG_SIZE)
+		if (size != 0)
 			memcpy(m_large_recv.data(), m_dir.buf_in->data, size);
 
 	} else {
@@ -360,6 +363,7 @@ bool IPCChannelEnd::recvWithTimeout(int timeout_ms) noexcept
 			if (!wait_in(&m_dir, timeout_ms_abs))
 				return false;
 		} while (size > IPC_CHANNEL_MSG_SIZE);
+		if (size != 0)
 			memcpy(recv_data, m_dir.buf_in->data, size);
 	}
 	return true;
@@ -382,18 +386,15 @@ std::pair<IPCChannelEnd, std::thread> make_test_ipc_channel(
 #endif
 	}();
 
-	auto resources_first = std::make_unique<IPCChannelResourcesSingleProcess>();
-	resources_first->setFirst(resource_data);
-
-	IPCChannelEnd end_a = IPCChannelEnd::makeA(std::move(resources_first));
-
 	std::thread thread_b([=] {
-		auto resources_second = std::make_unique<IPCChannelResourcesSingleProcess>();
-		resources_second->setSecond(resource_data);
+		auto resources_second = IPCChannelResourcesSingleProcess::makeSecond(resource_data);
 		IPCChannelEnd end_b = IPCChannelEnd::makeB(std::move(resources_second));
 
 		fun(std::move(end_b));
 	});
 
+	auto resources_first = IPCChannelResourcesSingleProcess::makeFirst(resource_data);
+	IPCChannelEnd end_a = IPCChannelEnd::makeA(std::move(resources_first));
+
 	return {std::move(end_a), std::move(thread_b)};
 }

src/threading/ipc_channel.h

@@ -56,7 +56,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 	* other posix: uses posix mutex and condition variable
 */
 
-#define IPC_CHANNEL_MSG_SIZE 0x2000U
+constexpr size_t IPC_CHANNEL_MSG_SIZE = 0x2000;
 
 struct IPCChannelBuffer
 {
@@ -83,6 +83,7 @@ struct IPCChannelBuffer
 	u8 data[IPC_CHANNEL_MSG_SIZE] = {};
 
 	IPCChannelBuffer();
+	DISABLE_CLASS_COPY(IPCChannelBuffer)
 	~IPCChannelBuffer(); // Note: only destruct once, i.e. in one process
 };
 
@@ -96,18 +97,8 @@ struct IPCChannelShared
 	IPCChannelBuffer b{};
 };
 
-struct IPCChannelDirection
-{
-	IPCChannelBuffer *buf_in;
-	IPCChannelBuffer *buf_out;
-#if defined(IPC_CHANNEL_IMPLEMENTATION_WIN32)
-	HANDLE sem_in;
-	HANDLE sem_out;
-#endif
-};
-
-// Each end holds this. One is A, one is B.
-// Implementors of this struct decide how to allocate buffers (i.e. malloc or mmap).
+// Interface for managing the shared resources.
+// Implementors decide whether to use malloc or mmap.
 struct IPCChannelResources
 {
 	// new struct, because the win32 #if is annoying
@@ -123,6 +114,15 @@ struct IPCChannelResources
 
 	Data data;
 
+	IPCChannelResources() = default;
+	DISABLE_CLASS_COPY(IPCChannelResources)
+
+	// Child should call cleanup().
+	// (Parent destructor can not do this, because when it's called the child is
+	// already dead.)
+	virtual ~IPCChannelResources() = default;
+
+protected:
 	// Used for previously unmanaged data_ (move semantics)
 	void setFirst(Data data_)
 	{
@@ -160,14 +160,6 @@ struct IPCChannelResources
 			cleanupNotLast();
 		}
 	}
-
-	IPCChannelResources() = default;
-	DISABLE_CLASS_COPY(IPCChannelResources)
-
-	// Child should call cleanup().
-	// (Parent destructor can not do this, because when it's called the child is
-	// already dead.)
-	virtual ~IPCChannelResources() = default;
 };
 
 class IPCChannelEnd
@@ -184,13 +176,15 @@ public:
 #endif
 	};
 
+	// Unusable empty end
 	IPCChannelEnd() = default;
 
+	// Construct end A or end B from resources
 	static IPCChannelEnd makeA(std::unique_ptr<IPCChannelResources> resources);
 	static IPCChannelEnd makeB(std::unique_ptr<IPCChannelResources> resources);
 
-	// Note: timeouts may be for receiving any response, not a whole message.
-	// If send, recv, or exchange return false (=timeout), stop using the channel.
+	// Note: Timeouts may be for receiving any response, not a whole message.
+	// Therefore, if a timeout occurs, stop using the channel.
 
 	// Returns false on timeout
 	[[nodiscard]]
@@ -276,6 +270,20 @@ struct IPCChannelResourcesSingleProcess final : public IPCChannelResources
 	}
 
 	~IPCChannelResourcesSingleProcess() override { cleanup(); }
+
+	static std::unique_ptr<IPCChannelResourcesSingleProcess> makeFirst(Data data)
+	{
+		auto ret = std::make_unique<IPCChannelResourcesSingleProcess>();
+		ret->setFirst(data);
+		return ret;
+	}
+
+	static std::unique_ptr<IPCChannelResourcesSingleProcess> makeSecond(Data data)
+	{
+		auto ret = std::make_unique<IPCChannelResourcesSingleProcess>();
+		ret->setSecond(data);
+		return ret;
+	}
 };
 
 // For testing

src/unittest/test_threading.cpp

@@ -235,7 +235,7 @@ void TestThreading::testIPCChannel()
 {
 	auto [end_a, thread_b] = make_test_ipc_channel([](IPCChannelEnd end_b) {
 		// echos back messages. stops if "" is sent
-		for (;;) {
+		while (true) {
 			UASSERT(end_b.recvWithTimeout(-1));
 			UASSERT(end_b.sendWithTimeout(end_b.getRecvData(), end_b.getRecvSize(), -1));
 			if (end_b.getRecvSize() == 0)
@@ -243,20 +243,29 @@ void TestThreading::testIPCChannel()
 		}
 	});
 
-	u8 buf[20000] = {};
-	for (int i = sizeof(buf); i > 0; i -= 100) {
-		buf[i - 1] = 123;
-		UASSERT(end_a.exchangeWithTimeout(buf, i, -1));
+	u8 buf1[20000] = {};
+	for (int i = sizeof(buf1); i > 0; i -= 100) {
+		buf1[i - 1] = 123;
+		UASSERT(end_a.exchangeWithTimeout(buf1, i, -1));
 		UASSERTEQ(int, end_a.getRecvSize(), i);
 		UASSERTEQ(int, reinterpret_cast<const u8 *>(end_a.getRecvData())[i - 1], 123);
 	}
 
+	u8 buf2[IPC_CHANNEL_MSG_SIZE * 3 + 10];
+	end_a.exchange(buf2, IPC_CHANNEL_MSG_SIZE * 3 + 10);
+	end_a.exchange(buf2, IPC_CHANNEL_MSG_SIZE * 3);
+	end_a.exchange(buf2, IPC_CHANNEL_MSG_SIZE);
+	end_a.exchange(buf2, IPC_CHANNEL_MSG_SIZE * 2);
+	end_a.exchange(buf2, IPC_CHANNEL_MSG_SIZE - 1);
+	end_a.exchange(buf2, IPC_CHANNEL_MSG_SIZE + 1);
+	end_a.exchange(buf2, 1);
+
 	// stop thread_b
-	UASSERT(end_a.exchangeWithTimeout(buf, 0, -1));
+	UASSERT(end_a.exchangeWithTimeout(nullptr, 0, -1));
 	UASSERTEQ(int, end_a.getRecvSize(), 0);
 
 	thread_b.join();
 
 	// other side dead ==> should time out
-	UASSERT(!end_a.exchangeWithTimeout(buf, 0, 200));
+	UASSERT(!end_a.exchangeWithTimeout(nullptr, 0, 200));
 }