Exceptions starting DDS can't be caught without running in a zone about sdk HOT 6 OPEN

@derekxu16 can you take a look when you have a chance?

from sdk.

Possibly related to this (but if not I can file another issue), the call to DartDevelopmentService.startDartDevelopmentService never completes when trying to connect to another instance of DDS when it's run in a zone (which is the only workaround I have for the above).

This code will never print 2, 3 or 4 (when run in debug mode such that it already has a DDS instance) :

import 'dart:async';
import 'dart:developer';

import 'package:dds/dds.dart';

Future<void> main() async {
  try {
    final serviceInfo = await Service.getInfo();

    // Try to connect DDS to an existing version in a zone to handle errors.
    final dds = await runZonedGuarded(
      () => DartDevelopmentService.startDartDevelopmentService(
          serviceInfo.serverUri!),
      (error, stack) {
        print('1: Failed to start DDS: $error');
      },
    );
    print('2: Done!');
  } catch (e) {
    print('3: Error: $e');
  }
  print('4: Done!');
}

This makes it a bit messy to spawn DDS in DAP, because we'd have to use a Zone, and then also a completer to continue when either an error occurs or startDartDevelopmentService completes (and then we need to ensure that if two errors occur in the handler, or an error occurs and it returns, we don't try to complete the completer twice).

from sdk.

Possibly related to this (but if not I can file another issue)

This issue felt familiar, so I did some digging and found this: flutter/flutter#141821

Basically, this is just the behavior of zones, which is kind of gross.

from sdk.

Ah, thanks for the info, that explains what I see. I handled this by using a completer in https://dart-review.googlesource.com/c/sdk/+/366662 but that's also quite gross, so if we could eliminate the need for a zone (the original issue here) we can remove than and just have the original simple try/catch :-)

from sdk.

@bkonyi, so is our goal here to make exceptions thrown when starting DDS catchable? This webSocketBuilder call currently doesn't run in a Zone with an error handler:

So I think that if we want to make exceptions thrown when starting DDS catchable, we have to wrap that webSocketBuilder call with a Completer + runZonedGuarded similarly to what @DanTup did in his CL.

from sdk.

Yeah, basically we just don't want unhandled asynchronous exceptions to leak out of DDS. If it makes sense to throw (e.g., if remoteVmServiceWsUri points to a VM service that doesn't exist) we should throw synchronously. If it makes sense to swallow an exception (e.g., the VM service connection disappears, which indicates we DDS should shutdown), we should do that and shutdown gracefully.

from sdk.