#include <cerrno>
#include <cstring>
#include <iostream>

#include <poll.h>
#include <stdint.h>
#include <time.h>

using std::endl;

//============================================================================
// :: Helpers

namespace
{
  // An RAII helper to measure the time blocked in poll()
  class Timer
  {
  public:
    // Remember our "start" time.
    Timer()
    {
      if (::clock_gettime(CLOCK_MONOTONIC, &m_start) == -1) {
        const int error = errno;
        std::cout
          << "Unable to initialize start time; elapsed time "
          " cannot be calculated: " << std::strerror(error) << endl;

        // Reset the seconds of our start time. We will use this to signify
        // that the time was not set correctly, since 0 would mean we have gone
        // back in time!
        m_start.tv_sec = 0;
      }
    }

    // Calculate how long it has been since we were constructed.
    ~Timer()
    {
      if (m_start.tv_sec == 0) {
        // Something went wrong during construction.  Don't do anything.
        return;
      }

      struct ::timespec end;
      if (::clock_gettime(CLOCK_MONOTONIC, &end) == -1) {
        const int error = errno;
        std::cout
          << ": Unable to initialize end time; elapsed time "
          " cannot be calculated: " << std::strerror(error) << endl;
        return;
      }

      // Calculate the amount of time elapsed in milliseconds. This will never
      // be used to calculate large times so don't worry about overflow here.
      uint64_t elapsedTime
        = (end.tv_sec * 1000 + end.tv_nsec / 1000000)
        - (m_start.tv_sec * 1000 + m_start.tv_nsec / 1000000);

      std::cout << "Elapsed time: " << elapsedTime << " ms" << endl;
    }

  private:
    // The time we were constructed.
    struct ::timespec m_start;
  };
}

//============================================================================
// :: Entry Point

int main()
{
  // A timer to determine how long we actually blocked in the call below.
  const Timer timer;

  // Block for a half second.  Ignore the number of file descriptors that have
  // revents set.  We aren't monitoring any fds.
  ::poll(NULL, 0, 500);

  return 0;
}