usql update

usql/threadpool.h

@@ -0,0 +1,79 @@
+#include <thread>
+#include <mutex>
+#include <functional>
+#include <queue>
+#include <condition_variable>
+#include <vector>
+
+class thread_pool {
+public:
+	thread_pool(std::size_t size) : stop(false) {
+		for (std::size_t i = 0; i < size; ++i) {
+			workers.emplace_back([this] { spawn(); });
+		}
+	}
+
+	virtual ~thread_pool() {
+		if (!stop) join();
+	}
+
+	void post(std::function<void()> f) {
+		{
+			std::unique_lock<std::mutex> lock(mutex);
+			tasks.push(f);
+		}
+
+		condition.notify_one();
+	}
+
+	void join() {
+		{
+			std::unique_lock<std::mutex> lock(mutex);
+			stop = true;
+		}
+
+		condition.notify_all();
+
+		for (std::size_t i = 0; i < workers.size(); ++i) {
+			workers[i].join();
+		}
+	}
+
+private:
+	void spawn() {
+		std::function<void()> task;
+		
+		bool task_queue_empty = tasks.empty();
+		while (!stop || !task_queue_empty) {
+			bool task_valid = false;
+			{
+				std::unique_lock<std::mutex> lock(mutex);
+				condition.wait(lock, [this]() {
+					return (!tasks.empty()) || (tasks.empty() && stop);
+				});
+
+				if (!tasks.empty()) {
+					task = std::move(tasks.front());
+					tasks.pop();
+					task_valid = true;
+				} 
+				
+				task_queue_empty = tasks.empty();
+			}
+
+			if (task_valid) task();
+		}
+	}
+
+public:
+	std::vector<std::thread> workers;
+	std::queue<std::function<void()>> tasks;
+
+	std::mutex mutex;
+	std::condition_variable condition;
+	bool stop;
+};
+
+inline void dispatch(thread_pool &pool, std::function<void()> f) {
+	pool.post(f);
+}