Update on Deno Watch Mode Signal Issue.

Avatar photoByAdil

There is an issue in Deno where the signal handler doesn’t work in watch mode. I believe this happens because the Deno file watcher doesn’t send the INT signal to the worker, causing it to just stop instead. I’m confident about this now.

source 

 select! {
      _ = receiver_future => {},
      _ = deno_signals::ctrl_c() => {
        return Ok(()); // this line handled the INT signal and fulfilled select!
      },
      _ = restart_rx.recv() => {
        print_after_restart();
        continue;
      },
      success = operation_future => {...}

In the Deno code, the select! statement acts like JavaScript’s Promise.any. It completes as soon as the INT signal is ignored. The operation_future runs the user’s JavaScript or TypeScript files, but it doesn’t get a chance to activate the user-defined listener.

I also looked at how Node.js handles signals in watch mode. It sends the signal to the worker and waits for the worker to finish.

source 

async function killAndWait(signal = kKillSignal, force = false) {
  child?.removeAllListeners();
  if (!child) {
    return;
  }
  if ((child.killed || exited) && !force) {
    return;
  }
  const onExit = once(child, 'exit');
  child.kill(signal);
  const { 0: exitCode } = await onExit;
  return exitCode;
}

I plan to use a similar approach: send the signal to the worker to trigger the listener and then wait for it to complete.

Similar Posts