Shouldn't the ProviderContainer.dispose() be asynchronous?

[dluksza]

What actually happens when ProviderContainer.dispose() is called and one of the onDispose callbacks is asynchronous?

I guess, since dispose is not asynchronous, it won't wait for the async disposal callback to finish. Most of the disposable things are actually asynchronous, like canceling stream subscription, closing stream controller, or websocket connection.

Not waiting for the disposal callbacks may theoretically lead to some resources being not fully disposed, or some events (in case of streams) being partially processed, or not processed at all. This is probably less concerning in the case of Flutter app, but it's more of an issue for command-line tools or server applications.

Would it be possible to make dispose asynchronous so that we can wait for all of the disposing callbacks to finish before we exit the app?

[rrousselGit]

This is a non-issue. Whether dispose is asynchronous or not, the Dart VM will still wait for all async operations to complete before quitting the app.

So awaiting ProviderContainer.dispose serves no purpose

[dluksza]

I'm implementing graceful exit on SIGINT to my command-line app and in this context, it seems that I need to await or something.

My signal handler looks like:

ProcessSignal.sigint.watch().listen((event) {
  container.dispose();
  exit(0);
});

I need to call exit(0), because otherwise, the process will hang forever. But this also means that DartVM won't wait for async operations to complete. It will just bailout. This is what I also see in my logs, some of the asynchronous disposal callbacks do not finish. If I add a Future.delayed(Duration(milliseconds: 500)) between dispose and exit then everything is disposed correctly.

In this use case having something to await on, before exiting the app would solve the issue.

[dluksza]

Out of curiosity, I've added await container.pump() between dispose() and exit(0) and this seems to wait until everything is properly disposed.

[rrousselGit]

pump is not doing what you want. It's not awaiting for dispose to complete. Rather it seems that your dispose functions complete really fast

[dluksza]

Well, they are not that fast to finish within dispose, but at least right now fast enough to finish within pump.

Anyway, would be good to have something to await for full disposal reliably, as you say the pump is just a coincidence.