Update Nemirtingas overlay to latest.

overlay_experimental/System/ThreadPool.hpp

@@ -0,0 +1,164 @@
+/*
+ * Copyright (C) Nemirtingas
+ * This file is part of System.
+ *
+ * System is free software; you can redistribute it
+ * and/or modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * System 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with the System; if not, see
+ * <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <atomic>
+#include <condition_variable>
+#include <functional>
+#include <future>
+#include <memory>
+#include <mutex>
+#include <queue>
+#include <thread>
+#include <type_traits>
+#include <vector>
+
+namespace System {
+class ThreadPool
+{
+    using task_t = std::function<void()>;
+
+    std::atomic<bool> _StopWorkers;
+    std::atomic<std::size_t> _ActiveCount;
+
+    std::condition_variable _WorkerNotifier;
+    std::mutex _Mutex;
+
+    std::vector<std::thread> _Workers;
+    std::queue<task_t> _Tasks;
+
+public:
+    explicit ThreadPool():
+        _ActiveCount(0)
+    {
+    }
+
+    ~ThreadPool()
+    {
+        Join();
+    }
+
+    ThreadPool(ThreadPool const &) = delete;
+    ThreadPool(ThreadPool&&) = default;
+
+    ThreadPool&operator=(ThreadPool const &) = delete;
+    ThreadPool&operator=(ThreadPool&&) = default;
+
+    template <class Func, class... Args>
+    auto Push(Func &&fn, Args &&...args)
+    {
+        using return_type = typename std::result_of<Func(Args...)>::type;
+
+        auto task{ std::make_shared<std::packaged_task<return_type()>>(
+            std::bind(std::forward<Func>(fn), std::forward<Args>(args)...)
+        ) };
+
+        auto future{ task->get_future() };
+        {
+            std::lock_guard<std::mutex> lock(_Mutex);
+
+            _Tasks.emplace([task]()
+            {
+                (*task)();
+            });
+        }
+        
+        _WorkerNotifier.notify_one();
+        return future;
+    }
+
+    // Remove all pending tasks from the queue
+    void Clear()
+    {
+        std::lock_guard<std::mutex> lock(_Mutex);
+        _Tasks = {};
+    }
+
+    // Stops all previous and creates new worker threads.
+    void Start(std::size_t worker_count = std::thread::hardware_concurrency())
+    {
+        Join();
+
+        _StopWorkers = false;
+        for (std::size_t i = 0; i < worker_count; ++i)
+            _Workers.emplace_back(std::bind(&ThreadPool::_WorkerLoop, this));
+    }
+
+    // Wait all workers to finish
+    void Join()
+    {
+        _StopWorkers = true;
+        _WorkerNotifier.notify_all();
+
+        for (auto &thread : _Workers)
+        {
+            if (thread.joinable())
+                thread.join();
+        }
+
+        _Workers.clear();
+    }
+
+    std::size_t WorkerCount() const
+    {
+        return _Workers.size();
+    }
+
+    // Get the number of active workers
+    std::size_t ActiveCount() const
+    {
+        return _ActiveCount;
+    }
+
+private:
+    void _WorkerLoop()
+    {
+        while (true)
+        {
+            auto task{ _NextTask() };
+
+            if (task)
+            {
+                ++_ActiveCount;
+                task();
+                --_ActiveCount;
+            }
+            else if (_StopWorkers)
+            {
+                break;
+            }
+        }
+    }
+
+    task_t _NextTask()
+    {
+        std::unique_lock<std::mutex> lock{ _Mutex };
+
+        _WorkerNotifier.wait(lock, [this]() { return !_Tasks.empty() || _StopWorkers; });
+
+        if (_Tasks.empty())
+            return {};
+
+        auto task{ _Tasks.front() };
+        _Tasks.pop();
+        return task;
+    }
+};
+}