The following code example is taken from the book
The C++ Standard Library - A Tutorial and Reference, 2nd Edition
by Nicolai M. Josuttis, Addison Wesley Longman, 2012
Copyright © 2012 by Pearson Education, Inc. and Nicolai M. Josuttis
#include <condition_variable>
#include <mutex>
#include <future>
#include <thread>
#include <iostream>
#include <queue>
std::queue<int> queue;
std::mutex queueMutex;
std::condition_variable queueCondVar;
void provider (int val)
{
// push different values (val til val+5 with timeouts of val milliseconds into the queue
for (int i=0; i<6; ++i) {
{
std::lock_guard<std::mutex> lg(queueMutex);
queue.push(val+i);
} // release lock
queueCondVar.notify_one();
std::this_thread::sleep_for(std::chrono::milliseconds(val));
}
}
void consumer (int num)
{
// pop values if available (num identifies the consumer)
while (true) {
int val;
{
std::unique_lock<std::mutex> ul(queueMutex);
queueCondVar.wait(ul,[]{ return !queue.empty(); });
val = queue.front();
queue.pop();
} // release lock
std::cout << "consumer " << num << ": " << val << std::endl;
}
}
int main()
{
// start three providers for values 100+, 300+, and 500+
auto p1 = std::async(std::launch::async,provider,100);
auto p2 = std::async(std::launch::async,provider,300);
auto p3 = std::async(std::launch::async,provider,500);
// start two consumers printing the values
auto c1 = std::async(std::launch::async,consumer,1);
auto c2 = std::async(std::launch::async,consumer,2);
}