Threading: Remove a level of indirection from Promise and Mailbox.

Makes using small copyable or POD objects in these more efficient, and if you want
to you can just put a pointer or smart pointer in there, which will
effectively do the same thing as the old setup.

Common/Thread/Channel.h

@@ -9,6 +9,7 @@
 // well as a simple blocking mailbox. Let's see if we get there.
 
 // Single item mailbox.
+// T is copyable. Often T will itself just be a pointer or smart pointer of some sort.
 template<class T>
 struct Mailbox {
 	Mailbox() : refcount_(1) {}
@@ -18,9 +19,9 @@ struct Mailbox {
 
 	std::mutex mutex_;
 	std::condition_variable condvar_;
-	T *data_ = nullptr;
+	T data_ = nullptr;
 
-	T *Wait() {
+	T Wait() {
 		std::unique_lock<std::mutex> lock(mutex_);
 		while (!data_) {
 			condvar_.wait(lock);
@@ -28,7 +29,7 @@ struct Mailbox {
 		return data_;
 	}
 
-	bool Poll(T **data) {
+	bool Poll(T *data) {
 		std::unique_lock<std::mutex> lock(mutex_);
 		if (data_) {
 			*data = data_;
@@ -38,7 +39,7 @@ struct Mailbox {
 		}
 	}
 
-	bool Send(T *data) {
+	bool Send(T data) {
 		std::unique_lock<std::mutex> lock(mutex_);
 		if (!data_) {
 			data_ = data;

Common/Thread/Promise.h

@@ -9,7 +9,7 @@
 template<class T>
 class PromiseTask : public Task {
 public:
-	PromiseTask(std::function<T *()> fun, Mailbox<T> *tx) : fun_(fun), tx_(tx) {
+	PromiseTask(std::function<T ()> fun, Mailbox<T> *tx) : fun_(fun), tx_(tx) {
 		tx_->AddRef();
 	}
 	~PromiseTask() {
@@ -17,11 +17,11 @@ public:
 	}
 
 	void Run() override {
-		T *value = fun_();
+		T value = fun_();
 		tx_->Send(value);
 	}
 
-	std::function<T *()> fun_;
+	std::function<T ()> fun_;
 	Mailbox<T> *tx_;
 };
 
@@ -32,7 +32,7 @@ public:
 template<class T>
 class Promise {
 public:
-	static Promise<T> *Spawn(ThreadManager *threadman, std::function<T *()> fun, TaskType taskType) {
+	static Promise<T> *Spawn(ThreadManager *threadman, std::function<T()> fun, TaskType taskType) {
 		Mailbox<T> *mailbox = new Mailbox<T>();
 
 		Promise<T> *promise = new Promise<T>();
@@ -50,8 +50,8 @@ public:
 		delete data_;
 	}
 
-	// Returns *T if the data is ready, nullptr if it's not.
-	T *Poll() {
+	// Returns T if the data is ready, nullptr if it's not.
+	T Poll() {
 		if (ready_) {
 			return data_;
 		} else {
@@ -66,7 +66,7 @@ public:
 		}
 	}
 
-	T *BlockUntilReady() {
+	T BlockUntilReady() {
 		if (ready_) {
 			return data_;
 		} else {
@@ -81,7 +81,7 @@ public:
 private:
 	Promise() {}
 
-	T *data_ = nullptr;
+	T data_ = nullptr;
 	bool ready_ = false;
 	Mailbox<T> *rx_;
 };

UI/MemStickScreen.cpp

@@ -645,7 +645,7 @@ UI::EventReturn ConfirmMemstickMoveScreen::OnConfirm(UI::EventParams &params) {
 	if (moveData_) {
 		progressReporter_.Set(iz->T("Starting move..."));
 
-		moveDataTask_ = Promise<MoveResult>::Spawn(&g_threadManager, [&]() -> MoveResult * {
+		moveDataTask_ = Promise<MoveResult *>::Spawn(&g_threadManager, [&]() -> MoveResult * {
 			Path moveSrc = g_Config.memStickDirectory;
 			Path moveDest = newMemstickFolder_;
 			if (moveSrc.GetFilename() != "PSP") {

UI/MemStickScreen.h

@@ -130,7 +130,7 @@ private:
 	ProgressReporter progressReporter_;
 	UI::TextView *progressView_ = nullptr;
 
-	Promise<MoveResult> *moveDataTask_ = nullptr;
+	Promise<MoveResult *> *moveDataTask_ = nullptr;
 
 	std::string error_;
 };

unittest/TestThreadManager.cpp

@@ -17,7 +17,7 @@ ResultObject *ResultProducer() {
 }
 
 bool TestMailbox() {
-	Mailbox<ResultObject> *mailbox = new Mailbox<ResultObject>();
+	Mailbox<ResultObject *> *mailbox = new Mailbox<ResultObject *>();
 	mailbox->Send(new ResultObject{ true });
 	ResultObject *data;
 	data = mailbox->Wait();
@@ -60,7 +60,7 @@ bool TestThreadManager() {
 	ThreadManager manager;
 	manager.Init(8, 1);
 
-	Promise<ResultObject> *object(Promise<ResultObject>::Spawn(&manager, &ResultProducer, TaskType::IO_BLOCKING));
+	Promise<ResultObject *> *object(Promise<ResultObject *>::Spawn(&manager, &ResultProducer, TaskType::IO_BLOCKING));
 
 	if (!TestParallelLoop(&manager)) {
 		return false;