Add a generic worker thread pool job executor mechanism

src/worker_thread.h

@@ -0,0 +1,55 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD 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, version 2.
+ * OpenTTD 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 OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file worker_thread.h Worker thread pool utility. */
+
+#ifndef WORKER_THREAD_H
+#define WORKER_THREAD_H
+
+#include <queue>
+#include <mutex>
+#include <condition_variable>
+#if defined(__MINGW32__)
+#include "3rdparty/mingw-std-threads/mingw.mutex.h"
+#include "3rdparty/mingw-std-threads/mingw.condition_variable.h"
+#endif
+
+typedef void WorkerJobFunc(void *, void *, void *);
+
+struct WorkerThreadPool {
+private:
+	struct WorkerJob {
+		WorkerJobFunc *func;
+		void *data1;
+		void *data2;
+		void *data3;
+	};
+
+	uint workers = 0;
+	bool exit = false;
+	std::mutex lock;
+	std::queue<WorkerJob> jobs;
+	std::condition_variable empty_cv;
+	std::condition_variable done_cv;
+
+	static void Run(WorkerThreadPool *pool);
+
+public:
+
+	void Start(const char *thread_name, uint max_workers);
+	void Stop();
+	void EnqueueJob(WorkerJobFunc *func, void *data1 = nullptr, void *data2 = nullptr, void *data3 = nullptr);
+
+	~WorkerThreadPool()
+	{
+		this->Stop();
+	}
+};
+
+extern WorkerThreadPool _general_worker_pool;
+
+#endif /* WORKER_THREAD_H */