(0 0 1 0) // (elements in queue 1, in queue 2, in queue 3, in queue 4)
(1 0 1 0)
(1 1 1 0)
(0 0 0 0)
(0 0 0 0)
(0 0 0 0)
(1 0 0 0)
(2 0 0 0)
(2 1 0 0)
(1 1 0 1)
(1 0 0 1)
(1 0 0 0)
(1 0 0 0)
(0 0 0 0)
(1 0 0 0)
...CTRL+c

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

using namespace std;

// modify this to modify the number of consumer threads
#define WORKERS_THREADS     4
// max size of each of four queues
#define MAX_QUEUE_SIZE      100
// debug
#define DEFAULTCOLOR        "33[0m"
#define RED                 "33[22;31m"
#define YELLOW              "33[1;33m"
#define GREEN               "33[0;0;32m"

class MultiQueue {
    public:
        void initThreadPool(void);
        void insert(int num);
        void remove(void);
        void insertPriorityQueue(int num);
        int removePriorityQueue(void);
        void printQueues(string what);
        int getQueue1Size(void);
        int getQueue2Size(void);
        int getQueue3Size(void);
        int getQueue4Size(void);
        int getPrioQueueSize(void);
    private:
        vector<thread> workers;

        queue<int>q1;
        queue<int>q2;
        queue<int>q3;
        queue<int>q4;

        priority_queue<int, vector<int>, greater<int>> prioq;

        // mutex for push/pop in priority queue
        mutex priority_queue_mutex;
        // 4 mutexes for each queue
        mutex m1, m2, m3, m4;
        // mutex for printing 4 queues size
        mutex print;

        // mutex for push/pop to priority_queue
        condition_variable prioq_cond;
        // 4 conds for consumer threads
        condition_variable w1, w2, w3, w4;
};

int MultiQueue::getQueue1Size() { return q1.size(); }

int MultiQueue::getQueue2Size() { return q2.size(); }

int MultiQueue::getQueue3Size() { return q3.size(); }

int MultiQueue::getQueue4Size() { return q4.size(); }

int MultiQueue::getPrioQueueSize() { return prioq.size(); }

void MultiQueue::initThreadPool(void) {
    for (int i=0; i<WORKERS_THREADS; i++) {
        workers.push_back(thread(&MultiQueue::remove, this));
        workers[i].detach();
    }
}

void MultiQueue::printQueues(string what) {
    lock_guard<mutex> l(print);
    if (what == "insert")
        cout << GREEN << '(' << getQueue1Size() << ' ' << getQueue2Size() << ' ' << getQueue3Size() << ' ' << getQueue4Size() << ')' << DEFAULTCOLOR << 'n' << flush;
    else
        cout << YELLOW << '(' << getQueue1Size() << ' ' << getQueue2Size() << ' ' << getQueue3Size() << ' ' << getQueue4Size() << ')' << DEFAULTCOLOR << 'n' << flush;
}

// called from producer thread to tell consumer threads
// what queues to pop() from
void MultiQueue::insertPriorityQueue(int num) {
    lock_guard<mutex> prio(priority_queue_mutex);
    prioq.push(num);
    prioq_cond.notify_one();
}

// called from consumer threads to see what queues
// have elements to pop() from
int MultiQueue::removePriorityQueue(void) {
    int ret = 0;
    unique_lock<mutex> prio(priority_queue_mutex);
    prioq_cond.wait(prio, [this] () { return getPrioQueueSize() > 0; });
    ret = prioq.top();
    prioq.pop();
    return ret;
}

// producer thread
void MultiQueue::insert(int num) {
    switch(num) {
        case 1: {
            unique_lock<mutex> locker(m1);
            w1.wait(locker, [this] () { return getQueue1Size() < MAX_QUEUE_SIZE; });
            q1.push(num);
            break;
        }
        case 2: {
            unique_lock<mutex> locker(m2);
            w2.wait(locker, [this] () { return getQueue2Size() < MAX_QUEUE_SIZE; });
            q2.push(num);
            break;
        }
        case 3: {
            unique_lock<mutex> locker(m3);
            w3.wait(locker, [this] () { return getQueue3Size() < MAX_QUEUE_SIZE; });
            q3.push(num);
            break;
        }
        case 4: {
            unique_lock<mutex> locker(m4);
            w4.wait(locker, [this] () { return getQueue4Size() < MAX_QUEUE_SIZE; });
            q4.push(num);
            break;
        }
        default: {
            cout << "number not 1, 2, 3 nor 4: " << num << 'n' << flush;
            break;
        }
    }
    printQueues("insert");
    insertPriorityQueue(num);
}

void MultiQueue::remove(void) {
    int which_queue = 0;
    while (true) {
        which_queue = removePriorityQueue();
        switch (which_queue) {
            case 1: {
                lock_guard<mutex> lock(m1);
                int ret = q1.front();
                q1.pop();
                printQueues("remove");
                break;
            }
            case 2: {
                lock_guard<mutex> lock(m2);
                int ret = q2.front();
                q2.pop();
                printQueues("remove");
                break;
            }
            case 3: {
                lock_guard<mutex> lock(m3);
                int ret = q3.front();
                q3.pop();
                printQueues("remove");
                break;
            }
            case 4: {
                lock_guard<mutex> lock(m4);
                int ret = q4.front();
                q4.pop();
                printQueues("remove");
                break;
            }
            default: {
                break;
            }
        }
    }
}

int main(void) {
    int random_num = 0;

    MultiQueue mq;
    mq.initThreadPool();

    default_random_engine eng((random_device())());
    uniform_int_distribution<int> idis(1, 4);
    while (true) {
        random_num = idis(eng);
        mq.insert(random_num);
    }

    return 0;
}