win32: Add ComWorker to run all COM function on same thread

meson.build

@@ -322,6 +322,7 @@ sources = [
 if is_windows
   sources += [
     'src/win32/Win32Main.cxx',
+    'src/win32/ComWorker.cxx',
   ]
 endif
 

src/win32/ComWorker.cxx

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2020 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+#include "ComWorker.hxx"
+#include "Log.hxx"
+#include "thread/Name.hxx"
+#include "util/Domain.hxx"
+#include "win32/Com.hxx"
+
+namespace {
+static constexpr Domain com_worker_domain("com_worker");
+}
+
+Mutex COMWorker::mutex;
+unsigned int COMWorker::reference_count = 0;
+std::optional<COMWorker::COMWorkerThread> COMWorker::thread;
+
+void COMWorker::COMWorkerThread::Work() noexcept {
+	FormatDebug(com_worker_domain, "Working thread started");
+	SetThreadName("COM Worker");
+	COM com{true};
+	while (true) {
+		if (!running_flag.test_and_set()) {
+			FormatDebug(com_worker_domain, "Working thread ended");
+			return;
+		}
+		while (!spsc_buffer.empty()) {
+			std::function<void()> function;
+			spsc_buffer.pop(function);
+			function();
+		}
+		event.Wait(200);
+	}
+}

src/win32/ComWorker.hxx

@@ -0,0 +1,110 @@
+/*
+ * Copyright 2020 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_WIN32_COM_WORKER_HXX
+#define MPD_WIN32_COM_WORKER_HXX
+
+#include <boost/lockfree/spsc_queue.hpp>
+#include <condition_variable>
+#include <mutex>
+#include <optional>
+
+#include "thread/Future.hxx"
+#include "thread/Mutex.hxx"
+#include "thread/Thread.hxx"
+#include "win32/WinEvent.hxx"
+#include <objbase.h>
+#include <windows.h>
+
+// Worker thread for all COM operation
+class COMWorker {
+private:
+	class COMWorkerThread : public Thread {
+	public:
+		COMWorkerThread() : Thread{BIND_THIS_METHOD(Work)} {}
+
+	private:
+		friend class COMWorker;
+		void Work() noexcept;
+		void Finish() noexcept {
+			running_flag.clear();
+			event.Set();
+		}
+		void Push(const std::function<void()> &function) {
+			spsc_buffer.push(function);
+			event.Set();
+		}
+
+		boost::lockfree::spsc_queue<std::function<void()>> spsc_buffer{32};
+		std::atomic_flag running_flag = true;
+		WinEvent event{};
+	};
+
+public:
+	static void Aquire() {
+		std::unique_lock locker(mutex);
+		if (reference_count == 0) {
+			thread.emplace();
+			thread->Start();
+		}
+		++reference_count;
+	}
+	static void Release() noexcept {
+		std::unique_lock locker(mutex);
+		--reference_count;
+		if (reference_count == 0) {
+			thread->Finish();
+			thread->Join();
+			thread.reset();
+		}
+	}
+
+	template <typename Function, typename... Args>
+	static auto Async(Function &&function, Args &&...args) {
+		using R = std::invoke_result_t<std::decay_t<Function>,
+					       std::decay_t<Args>...>;
+		auto promise = std::make_shared<Promise<R>>();
+		auto future = promise->get_future();
+		thread->Push([function = std::forward<Function>(function),
+			      args = std::make_tuple(std::forward<Args>(args)...),
+			      promise = std::move(promise)]() mutable {
+			try {
+				if constexpr (std::is_void_v<R>) {
+					std::apply(std::forward<Function>(function),
+						   std::move(args));
+					promise->set_value();
+				} else {
+					promise->set_value(std::apply(
+						std::forward<Function>(function),
+						std::move(args)));
+				}
+			} catch (...) {
+				promise->set_exception(std::current_exception());
+			}
+		});
+		return future;
+	}
+
+private:
+	static Mutex mutex;
+	static unsigned int reference_count;
+	static std::optional<COMWorkerThread> thread;
+};
+
+#endif