test_cv_ping_pong.cpp

#include <thread>
#include <mutex>
#include <condition_variable>
#include <stdio.h>

std::mutex mtx;
std::condition_variable cv;

// number of players
const int tot = 2;
// current turn
int turn = 0;
// moves done by each thread
int count[tot] = {};
// total moves
int tot_count = 0;
// total moves limit
const int limit = 100000;

void dump_status() {
    printf("turn: %d\ncount[0]: %d\ncount[1]: %d\ntot_count: %d\n", turn, count[0], count[1], tot_count);
}

template<typename FnT>
void wait_or_die(int id, std::condition_variable &cv, std::unique_lock<std::mutex> &lk, FnT fn) {
    const int timeout = 5;
    if(!cv.wait_for(lk, std::chrono::seconds(timeout), fn)) {
        printf("Wait expired in thread %d after %d seconds\nStatus dump:\n", id, timeout);
        dump_status();
        std::abort();
    }
}

void thread_fn(int id) {
    // initial sync - let in only who is at the right turn
    {
        std::unique_lock<std::mutex> lk(mtx);
        while(turn != id) wait_or_die(id, cv, lk, [] { return true; });
    }
    for(;;) {
        std::unique_lock<std::mutex> lk(mtx);
        // "I was here"
        count[id]++;
        tot_count++;
        // pass hand
        turn = (turn + 1) % tot;
        cv.notify_all();
        // quit at the end
        if(tot_count >= limit) break;
        // wait for my turn
        wait_or_die(id, cv, lk, [&] { return turn == id; });
    }
}

int main() {
    // play the game
    std::thread thr(thread_fn, 1);
    thread_fn(0);

    // wait for exit
    thr.join();

    // summary
    dump_status();
    return 0;
}