monitor-fd-test.cc

#include <thread>
#include <mutex>
#include <iostream>
extern "C" {
  #include <poll.h>
  #include <unistd.h>
}

std::mutex stdio_mutex;

static void monitor_thread(int fd) {
  struct pollfd fds[1];
  fds[0].fd = fd;
  fds[0].events = 0;
  poll(fds, 1, -1);
  {
    std::lock_guard<std::mutex> guard(stdio_mutex);
    std::cerr << "Poll returned: " << fds[0].revents << '\n';
  }
}

int main(int argc, char ** argv) {
  int pipe_fds[2];
  if (pipe(pipe_fds) == -1)
    return 1;
  std::thread t(monitor_thread, pipe_fds[0]);
  {
    std::lock_guard<std::mutex> guard(stdio_mutex);
    std::cerr << "Thread forked\n";
  }
  close(pipe_fds[1]);
  sleep(10);
  {
    std::lock_guard<std::mutex> guard(stdio_mutex);
    std::cerr << "FD closed\n";
  }
  t.join();
  return 0;
}