[C++知识库]C++ 线程安全的队列

无界队列

#include<queue>
#include<mutex>
#include<condition_variable>
#include<optional>
#include<cassert>
#include<thread>

template<typename T,typename Container = std::queue<T>>
class Queue	//无界队列
{
public:
	Queue() = default;
	~Queue() = default;

	//禁止拷贝和移动，编译器会自动delete
	/*Queue(const Queue&) = delete;
	Queue(Queue&&) = delete;
	Queue& operator=(const Queue&) = delete;
	Queue& operator=(Queue&&) = delete;*/


	void push(const T& val)
	{
		emplace(val);
	}

	void push(T&& val)
	{
		emplace(std::move(val));
	}
	
	template<typename...Args>
	void emplace(Args&&...args)
	{
		std::lock_guard lk{ mtx_ };
		q_.push(std::forward<Args>(args)...);
		cv_.notify_one();
	}

	T pop()//阻塞
	{
		std::unique_lock lk{ mtx_ };
		cv_.wait(lk, [this] {return !q_.empty(); });//如果队列不为空就继续执行，否则阻塞
		assert(!q_.empty());
		T ret{ std::move_if_noexcept(q_.front()) };
		q_.pop();
		return ret;
	}


	std::optional<T> try_pop()//非阻塞
	{
		std::unique_lock lk{ mtx_ };
		if (q_.empty())return {};
		std::optional<T> ret{ std::move_if_noexcept(q_.front()) };
		q_.pop();
		return ret;
	}
	bool empty()const
	{
		std::lock_guard lk{ mtx_ };
		return q_.empty();
	}
private:
	Container q_;
	mutable std::mutex mtx_;
	std::condition_variable cv_;
};

#include<iostream>
int main()
{
	Queue<int>q;
	std::thread t1(
		[&] {
			for (int i = 0; i < 100; ++i)
			{
				q.push(i);
			}
		});

	std::thread t2(
		[&] {
			for (int i = 0; i < 100; ++i)
			{
				//std::cout<<q.pop()<<" ";
				if (auto ret = q.try_pop())
				{
					std::cout << *ret<<" ";
				}
			}
		});
	t1.join();
	t2.join();
	return 0;
}

有界队列

#include<mutex>
#include<condition_variable>
#include<boost/circular_buffer.hpp>
#include<optional>

template<typename T>
class Queue
{
public:
	Queue(size_t capacity) :q_{ capacity }{}

	template<typename T>
	void push(T&& val)//阻塞
	{
		std::unique_lock lk{ mtx_ };
		not_full_.wait(lk, [this] {return !q_.full(); });
		assert(!q_.full());
		q_.push_back(std::move(std::forward<T>(val)));
		not_empty_.notify_one();
	}

	template<typename T>
	bool try_push(T&& val)//非阻塞
	{
		std::lock_guard lk{ mtx_ };
		if (q_.full())return false;
		q_.push_back(std::forward<T>(val));
		not_empty_.notify_one();
		return true;
	}

	T pop()//阻塞
	{
		std::unique_lock lk{ mtx_ };
		not_empty_.wait(lk, [this] {return !q_.empty(); });
		asert(!q_.empty());
		T ret{ std::move_if_noexcept(q_.front()) };
		q_.pop_front();
		not_full_.notify_one();
		return ret;

	}
	std::optional<T> try_pop()//非阻塞
	{
		std::lock_guard lk{ mtx_ };
		if (q_.empty())return {};
		std::optional<T> ret{ std::move_if_noexcept(q_.front()) };
		q_.pop_front();
		not_full_.notify_one();
		return ret;
	}

private:
	boost::circular_buffer<T>q_;
	std::mutex mtx_;
	std::condition_variable not_full_;
	std::condition_variable not_empty_;
};

#include<iostream>
int main()
{
	Queue<int>q(10);
	std::thread t1(
		[&] {
			for (int i = 0; i < 100; ++i)
			{
				q.push(i);
			}
		});

	std::thread t2(
		[&] {
			for (int i = 0; i < 100; ++i)
			{
				//std::cout<<q.pop()<<" ";
				if (auto ret = q.try_pop())
				{
					std::cout << *ret << " ";
				}
			}
		});
	t1.join();
	t2.join();
	return 0;
}