DebugAdapterException thread was not found during `flutter debug-adapter`

[christopherfujino]

Describe the bug

Flutter Beta 3.10.0-1.4.pre (with dds v2.7.9) was just released yesterday April 26. There is one crash with a DebugAdapterException:

DebugAdapterException: DebugAdapterException: Thread 107 was not found
at IsolateManager.resumeThread(isolate_manager.dart:263)
at IsolateManager._handlePause(isolate_manager.dart:479)
at <asynchronous gap>(async)
at IsolateManager.handleEvent(isolate_manager.dart:178)
at <asynchronous gap>(async)
at DartDebugAdapter.handleDebugEvent(dart.dart:2076)
at <asynchronous gap>(async)
at DartDebugAdapter._withErrorHandling(dart.dart:2417)
at <asynchronous gap>(async)

To Reproduce
flutter debug_adapter

Please complete the following information:

• Operating System and version: Windows [Version 10.0.22621.1631]
• VS Code version: unknown
• Dart extension version: unknown
• Dart/Flutter SDK version: Flutter 3.10.0-1.4.pre
• Target device (if the issue relates to Flutter debugging): Unknown

[DanTup]

Hmm, this one is a little odd. This error is thrown when we can't find a thread using an ID we assigned. As far as I can tell, the only way that happens is if we have already processed the IsolateExit event.

So I suspect here we got both an IsolatePause and an IsolateExit event, but maybe due to awaits, we finished processing the IsolateExit before we finished processing the pause. However, we shouldn't really get an IsolateExit if an isolate was paused, because we haven't unpaused it yet.

So like with one of the previous fixes, my feeling is that either:

• This is happening during shutdown, so the Isolate exited because the app was closing (and not that it was unpaused and finished)
• There are two debuggers attached, and the other one unpaused the isolate (and it exited) while we were trying to handle the pause

I'll add some handling for this anyway. We should probably keep knowledge of exited events around (similar to the VM keeping Sentinels) and that way we can be sure when we're just trying to process an exited isolate (in which case we can silently do nothing) as opposed to the client sent us a bogus thread ID and we want to fail the request.

[christopherfujino]

There are two debuggers attached, and the other one unpaused the isolate (and it exited) while we were trying to handle the pause

Is having multiple debuggers attached supported? Could we have a second debugger attaching somehow notify the first?

[DanTup]

It doesn't work properly today, but there are some new APIs each debugger can start using to help. For example when a new isolate starts (paused) we normally send our breakpoints and then unpause it. For multiple debuggers, they need to instead send their breakpoints and then tell DDS they are ready for it to be unpaused (and DDS will unpause it when all clients are ready).

It requires all of the connected debuggers use those new APIs though. Currently (as far as I know), none of legacy DAP, new DAP, IntelliJ or DevTools implement these APIs.

If you see a lot of these, then I suspect it's more likely a race during shutdown (or a restart) because I don't expect many people are attaching two debuggers. Hard to say for sure without a repo, but there's no reason not to change this code to treat exited isolates different to invalid IDs (currently it assumes any ID it can't find is invalid and it should throw), and then all calling code just needs to decide what to do when an isolate it wanted to interact with has since exited (most likely by just doing nothing).

I should be able to get a fix for this tomorrow. I don't know whether it makes most sense to try and CP immediately, or try to get a better idea of how often it's happening though?

[christopherfujino]

I should be able to get a fix for this tomorrow. I don't know whether it makes most sense to try and CP immediately, or try to get a better idea of how often it's happening though?

I think our options are either get a CP out ASAP or risk not enabling DAP on stable.

[DanTup]

I have a fix open at https://dart-review.googlesource.com/c/sdk/+/299640.

If we want to cherry-pick this, we need a DDS release that matches the 2.7.9 release + this fix, for ex:

git checkout facfcf0f92ed28173f4fad9a3d21a90409582367
git cherry-pick [hash of newly landed change]
pub publish --dry-run (etc.)

If we just publish from master we would get some refactoring from dart-lang/sdk@5ef021b that we probably don't want to risk including.

@bkonyi FYI

[christopherfujino]

If we just publish from master we would get some refactoring from dart-lang/sdk@5ef021b that we probably don't want to disk including.

Agreed, I don't believe a hotfix rolling DDS to latest will be approved.

[bkonyi]

I've published 2.7.10 based on facfcf0f92ed28173f4fad9a3d21a90409582367 with 14ab84ebb30f180f46acec3e1d9a59d680622530 cherry picked.

[DanTup]

@bkonyi thank you!

The bot has opened flutter/flutter#125801 to roll this into master, which will be the change to cherry-pick.

[christopherfujino]

Thanks @bkonyi & @DanTup, I'll work on ensuring this is merged to master and file the request to CP 2.7.10 to beta.