C++ 并发编程练习15 “最简单的线程池”

下面的代码展示了一个简单的线程池。

#include 
#include 
#include 
#include 
#include 
#include 
#include 

template
class thread_safe_queue
{
private:
	mutable std::mutex mut;
	std::queue data_queue;
	std::condition_variable data_cond;

public:
	thread_safe_queue() {};
	void push(T new_value)
	{
		std::lock_guard lk(mut);
		data_queue.push(std::move(new_value));
		data_cond.notify_one();
	}

	void wait_and_pop(T& value)
	{
		std::unique_lock lk(mut);
		data_cond.wait(lk, [this] {return !data_queue.empty(); });
		value = std::move(data_queue.front());
		data_queue.pop();

	}

	std::shared_ptr  wait_and_pop()
	{
		std::unique_lock lk(mut);
		data_cond.wait(lk, [this] {return !data_queue.empty(); });

		std::shared_ptr res(std::make_shared(std::move(data_queue.front())));
		data_queue.pop();
		return res;
	}

	bool try_pop(T& value)
	{
		std::lock_guard lk(mut);
		if (data_queue.empty())
			return false;

		value = std::move(data_queue.front());
		data_queue.pop();
		return true;
	}

	std::shared_ptr try_pop()
	{
		std::unique_lock lk(mut);
		if (data_queue.empty())
			return std::shared_ptr();

		std::shared_ptr res(std::make_shared(std::move(data_queue.front())));
		data_queue.pop();
		return res;
	}

	bool empty() const
	{
		std::lock_guard lk(mut);
		return data_queue.empty();
	}
};

class join_threads
{
	std::vector threads;
public:
	explicit join_threads(std::vector threads_)
		: threads(threads_)
	{};

	~join_threads()
	{
		for (unsigned long i = 0; i < threads.size(); ++i)
		{
			if (threads[i].joinable())
				threads[i].join();
		}
	};
};

class thread_pool
{
    std::atomic_bool done;
    thread_safe_queue > work_queue;
	std::vector threads;
	join_threads joiner;

	void woker_thread()
	{
		while (!done)
		{
			std::function task;
			if (work_queue.try_pop(task))
				task();
			else
				std::this_thread::yield();
		}
	}

public:
	thread_pool()
		:done(false)
		,joiner(threads)
	{
		unsigned const thread_count = std::thread::hardware_concurrency();
		try
		{
			for (unsigned i = 0; i < thread_count; ++i)
			{
				threads.push_back(std::thread(&thread_pool::woker_thread, this));
			}
		}
		catch (...)
		{
			done = true;
			throw;
		}
	}

	~thread_pool()
	{
		done = true;
	}

	template
	void submit(FunctionType f)
	{
		work_queue.push(std::function(f));
	}
};

int main()
{
    std::cout << "Hello World!\n";
}