std::condition_variable 条件变量

std::condition_variable 条件变量

void wait( std::unique_lock<std::mutex>& lock ); #1
template< class Predicate >
void wait( std::unique_lock<std::mutex>& lock, Predicate stop_waiting ); #2

例1 ：

#include <iostream>
#include <string>
#include <thread>
#include <mutex>
#include <condition_variable>

std::mutex m;
std::condition_variable cv;
std::string data;
bool ready = false;
bool processed = false;

void worker_thread()
{
	std::unique_lock lk(m);
	cv.wait(lk, [] { return ready; });

	std::cout << "Worker thread is processing data\n";
	data += " after processing";

	processed = true;
	std::cout << "Worker thread signals data processing completed\n";

	lk.unlock();
	cv.notify_one();
}

int main()
{
	std::thread worker(worker_thread);

	data = "Example data";
	{
		std::lock_guard lk(m);
		ready = true;
		std::cout << "main() signals data ready for processing\n";
	}
	cv.notify_one();

	{
		std::unique_lock lk(m);
		cv.wait(lk, [] { return processed; });
	}
	std::cout << "Back in main(), data = " << data << '\n';

	worker.join();
}