producer-consumer in C++11

gistfile1.cpp

#include <thread>
#include <iostream>
#include <queue>

std::mutex mx;
std::condition_variable cv;
std::queue<int> q;

bool finished = false;

void producer(int n) {
	for(int i=0; i<n; ++i) {
		{
			std::lock_guard<std::mutex> lk(mx);
			q.push(i);
			std::cout << "pushing " << i << std::endl;
		}
		cv.notify_all();
	}
	{
		std::lock_guard<std::mutex> lk(mx);
		finished = true;
	}
	cv.notify_all();
}

void consumer() {
	while (true) {
		std::unique_lock<std::mutex> lk(mx);
		cv.wait(lk, []{ return finished || !q.empty(); });
		while (!q.empty()) {
			std::cout << "consuming " << q.front() << std::endl;
			q.pop();
		}
		if (finished) break;
	}
}

int main() {
	std::thread t1(producer, 10);
	std::thread t2(consumer);
	t1.join();
	t2.join();
	std::cout << "finished!" << std::endl;
}

thanks for your contribution :).but thread switching is very poor.is it correct??

Hi folk!
You are missing

#include <mutex>
#include <condition_variable> 

for the example to work seamlessly.
Regards ;)

Hello All,

Could you please explain me line no 30 ( cv.wait(lk, []{ return finished || !q.empty(); }); ) and how does condition variable knows which threads are using it and how it notifies other thread, or if you could explain me condition variable usage in this program?

Thanks,
Amit

If you quit line 14:

std::lock_guard<std::mutex> lk(mx);

the producer don't wait to consumer finishes.

How producer will come to know that consumer has done its job in case consumer is scheduled for long time? This situation may arise as below

1. producer thread scheduled at first and all the data pushed to queue.
2. consumer thread is working and consumed all the data but still running.