Just a quick example to demonstrate information passing between two thread without a mutex.

main.cpp

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


/*
 *   This program demonstrate that using one thread to write and another to read is ok to get ordered values from a queue. 
 *  
 *   One thread generate a ordered sequence of number, another consumes print the sequence
 *   the queue do its job to make sure the sequence order is correct.
 *
 *   To run this: 
 *       g++ main.cpp -o test -std=c++17 && ./test
 *       
 *   Running this will generate this: 
 *       getting: pushing stuff 0 queue size: 20 
 *       getting: pushing stuff 0 queue size: 30
 *       getting: pushing stuff 1 queue size: 40
 *       getting: pushing stuff 0 queue size: 51
 *       
 */

std::queue<std::string> my_queue;

void push_stuff_in(int num) {
    for (int i = 0; i < num; i++) {
        std::string m = "pushing stuff " + std::to_string(i);
        my_queue.push(m);
        std::this_thread::sleep_for(std::chrono::milliseconds(50));
    }
}

void get_stuff_out() {
    while (!my_queue.empty()) {
        auto entry = my_queue.front();
        std::cout << "getting: " << entry << " queue size: " << my_queue.size()
                  << std::endl;
        std::this_thread::sleep_for(std::chrono::milliseconds(600));
        my_queue.pop();
    }
}

int main() {
    std::thread t1{[]() {
        int cnt = 0;
        while (true) {
            cnt++;
            push_stuff_in(cnt);
        }
    }};

    std::thread t2{[]() {
        while (true) {
            get_stuff_out();
            std::this_thread::sleep_for(std::chrono::seconds(1));
        }
    }};

    t2.join();
    t1.join();

    return 0;
}