condition_variable/example8.cpp

// condition_variable::notify_one
#include <iostream>           // std::cout
#include <thread>             // std::thread
#include <mutex>              // std::mutex, std::unique_lock
#include <condition_variable> // std::condition_variable

std::mutex mtx;
std::condition_variable produce,consume;

int cargo = 0;     // shared value by producers and consumers

void consumer () {
 std::unique_lock<std::mutex> lck(mtx);
 while (cargo==0) consume.wait(lck);
 std::cout << cargo << '\n';
 cargo=0;
 produce.notify_one();
}

void producer (int id) {
 std::unique_lock<std::mutex> lck(mtx);
 while (cargo!=0) produce.wait(lck);
 cargo = id;
 consume.notify_one();
}

int main ()
{
 std::thread consumers[10],producers[10];
 // spawn 10 consumers and 10 producers:
 for (int i=0; i<10; ++i) {
   consumers[i] = std::thread(consumer);
   producers[i] = std::thread(producer,i+1);
 }

 // join them back:
 for (int i=0; i<10; ++i) {
   producers[i].join();
   consumers[i].join();
 }

 return 0;
}