producer.cpp

#include <condition_variable>
#include <mutex>
#include <thread>
#include <iostream>
#include <queue>
#include <chrono>

using namespace std;

class Queue {
 public:
  int pop() {
    unique_lock<std::mutex> mlock(mutex);
    while (queue.empty()) {
      cond.wait(mlock);
    }
    int item = queue.front();
    queue.pop();
    cond.notify_one();
    return item;
  }

  void push(const int item) {
    unique_lock<std::mutex> mlock(mutex);
    while(queue.size() >= 4) {
      printf("full queue, waiting\n");
      cond.wait(mlock);
    }

    queue.push(item);
    mlock.unlock();
    cond.notify_one();
  }

  int size() {
    return queue.size();
  }

 private:
  std::queue<int> queue;
  std::mutex mutex;
  std::condition_variable cond;
};

int main() {
    Queue q12;
    Queue q13;
    Queue q24;
    Queue q34;

    std::thread t1([&]() {
      int counter = 0;
      while(true) {
        std::this_thread::sleep_for(std::chrono::milliseconds(500));
        q12.push(counter);
        printf("t1 sending %d (q12 size: %d)\n", counter, q12.size());
        counter += 1;

        std::this_thread::sleep_for(std::chrono::milliseconds(500));
        q13.push(counter);
        printf("t1 sending %d (q13 size: %d)\n", counter, q13.size());
        counter += 1;
      }
    });

    std::thread t2([&]() {
      while(true) {
        //std::this_thread::sleep_for(std::chrono::milliseconds(500));
        int a = q12.pop();
        printf("t2 received a=%d\n", a);

        //std::this_thread::sleep_for(std::chrono::milliseconds(500));
        int b = q12.pop();
        printf("t2 received b=%d\n", b);
        q24.push(a+b);
        printf("t2 sending %d (q24 size: %d)\n", a+b, q24.size());
      }
    });

    std::thread t3([&]() {
      while(true) {
        //std::this_thread::sleep_for(std::chrono::milliseconds(500));
        int x = q13.pop();
        printf("t3 received x=%d\n", x);

        //std::this_thread::sleep_for(std::chrono::milliseconds(500));
        q34.push(x*2);
        printf("t3 sending %d (q34 size: %d)\n", x*2, q34.size());
      }
    });

    std::thread t4([&]() {
      while(true) {
        //std::this_thread::sleep_for(std::chrono::milliseconds(500));
        int a = q24.pop();
        printf("t4 received a=%d\n", a);

        //std::this_thread::sleep_for(std::chrono::milliseconds(500));
        int b = q34.pop();
        printf("t4 received b=%d\n", b);
        printf("a+b=%d\n", a+b);
      }
    });

    t1.join();
    t2.join();
    t3.join();
    t4.join();
}