C++ timer example

timer_main.cpp

#include <iostream>
#include <set>

extern "C" {
#include "unistd.h"
#include <sys/timerfd.h>
}

int main() {
    std::set<int> timerFds;

    fd_set readfds;
    FD_ZERO(&readfds);

    size_t n = 10;
    int maxFd = 0;
    for (size_t i = 1; i <= n; ++i) {
        int fd = timerfd_create(CLOCK_REALTIME, 0);
        maxFd = std::max(fd, maxFd);

        itimerspec spec;
        spec.it_value = { (long)i, 0 };
        spec.it_interval = { 0, 0 };
        timerfd_settime(fd, 0, &spec, nullptr);

        timerFds.emplace(fd);
    }

    timespec timeout = { 2, 0 };

    sleep(10);

    while (1) {
        for (const int& fd : timerFds) {
            FD_SET(fd, &readfds);
        }

        int availableFds = pselect(maxFd + 1, &readfds, nullptr, nullptr, &timeout, nullptr);
        std::cout << "Available file descriptors: " << availableFds << std::endl;

        if (availableFds > 0) {
            for (const int& fd : timerFds) {
                if (FD_ISSET(fd, &readfds)) {
                    std::cout << "Found file descriptor: " << fd << std::endl;

                    uint64_t val;
                    read(fd, &val, sizeof(val));
                    std::cout << "Read from file descriptor " << fd << ", value: " << val << std::endl;

                    itimerspec spec = { {0, 0}, {0, 0} };
                    timerfd_settime(fd, 0, &spec, nullptr);
                }
            }
        }
        else {
            break;
        }
    }

    return 0;
}