Method launchTimer

src/windows/libwinio.cpp:348–391

Try<Nothing> EventLoop::launchTimer(
    const Duration& duration, const lambda::function<void()>& callback)
{
  // Create a non-inheritable, manual reset, unnamed timer.
  HANDLE timer = ::CreateWaitableTimerW(nullptr, true, nullptr);
  if (timer == nullptr) {
    return WindowsError();
  }

  // If you give a positive value, then the timer call interprets it as
  // absolute time. A negative value is interpretted as relative time.
  // 0 is run immediately. The resolution is in 100ns.
  LARGE_INTEGER time_elapsed;
  time_elapsed.QuadPart = -duration.ns() / 100;

  TimerOverlapped* overlapped =
    new TimerOverlapped{timer, time_elapsed, callback};

  // We don't actually set the timer here since APCs only execute in the same
  // thread that called the async function. So, we queue the function call to
  // the IOCP so the event loop thread can queue the APC.
  //
  // NOTE: `::PostQueuedCompletionStatus` does not process the second to fourth
  // arguments, so you can give anything for them. Specifically, the overlapped
  // parameter doesn't need to point to a `OVERLAPPED` structure. See
  // https://msdn.microsoft.com/en-us/library/windows/desktop/aa365458(v=vs.85).aspx // NOLINT(whitespace/line_length)
  const BOOL success = ::PostQueuedCompletionStatus(
      iocp_handle_.get(),
      0,
      KEY_TIMER,
      reinterpret_cast<OVERLAPPED*>(overlapped));

  if (!success) {
    // Failing `PostQueuedCompletionStatus` means we have to clean the
    // memory here, since the APC won't execute.
    WindowsError error;
    delete overlapped;
    ::CloseHandle(timer);
    return error;
  }

  // The APC callback will clean up the memory and handle, so we can return.
  return Nothing();
}


// NOTE: The following functions use `int_fd` instead of the native Win32