#include <iostream>
#include <vector>
#include <thread>
#include <functional>
#include <chrono>
#include <mutex>
std::mutex mtx;    // LINE-1
 
class MessageQueue {
private:
    int total_elems;
    int n;
public:
    MessageQueue() : total_elems(0) {}
 
    void enqueue(int num_elems) {
        std::lock_guard<std::mutex> lock(mtx);    // LINE-2
        n = num_elems;
        int delay = (int)((double)std::rand() / (double)(RAND_MAX) * 10);
        std::this_thread::sleep_for(std::chrono::milliseconds(delay));
        total_elems += n;
    }
 
    void dequeue(int num_elems) {
        std::lock_guard<std::mutex> lock(mtx);    // LINE-3
        n = num_elems;
        int delay = (int)((double)std::rand() / (double)(RAND_MAX) * 10);
        std::this_thread::sleep_for(std::chrono::milliseconds(delay));
        total_elems -= n;
    }
 
    int getElemsCount() {
        return total_elems;
    }
};
 

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