asking for c++ design system, I asked to write c++ system that run 3 threads parallel and every thread print it's on charcter only, the order must be kept.
example : the print will be : abcabcabc .... , another question : about memory allocation, mutex, semaphore.

Question

asking for c++ design system, I asked to write c++ system that run 3 threads parallel  and every thread print it's on charcter only, the order must be kept. 
example : the print will be : abcabcabc .... , another question : about memory allocation, mutex, semaphore.

Sigiloso · Accepted Answer

create worker thread, create class has state, when reach the state it print the charcter. 
use one common mutex for the class .  save state and number of threads , it is the counter.  counter + = 1; counter = counter % num_threads;
this is to make sure it turn will not pass the number of threads. 
before destructions wait until all threads will finished the job.

the worker function example : 
void worker(std::stop_token st, int id, char ch)
{
    std::stop_callback callback(st, [this] {
        _cv.notify_all();
    });

while (true) {
        std::unique_lock lock(_mtx);

_cv.wait(lock, [&] {
            return _turn == id || st.stop_requested();
        });

if (st.stop_requested()) {
            std::cout << "worker id " << id << " stopped
";
            return;
        }

std::cout << "print " << ch << std::endl;

_turn = (_turn + 1) % _threadCount;
        _cv.notify_all();
    }
}

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