Connecting to new app throws stream exception

[kenzieschmoll]

[ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: Bad state: Already cancelled
#0      StreamQueue._checkNotClosed (package:async/src/stream_queue.dart:521:20)
#1      StreamQueue.cancel (package:async/src/stream_queue.dart:390:5)
#2      DdsExtension.onEventWithHistory.<anonymous closure> (package:dds/vm_service_extensions.dart:94:20)
#3      _rootRun (dart:async/zone.dart:1420:47)
#4      _CustomZone.run (dart:async/zone.dart:1328:19)
#5      _FutureListener.handleWhenComplete (dart:async/future_impl.dart:203:18)
#6      Future._propagateToListeners.handleWhenCompleteCallback (dart:async/future_impl.dart:737:39)
#7      Future._propagateToListeners (dart:async/future_impl.dart:793:11)
#8      Future._addListener.<anonymous closure> (dart:async/future_impl.dart:466:9)
#9      _microtaskLoop (dart:async/schedule_microtask.dart:40:21)
#10     _startMicrotaskLoop (dart:async/schedule_microtask.dart:49:5)

CC @bkonyi - is there a certain way we are supposed to be handling / cancelling calls to onEventWithHistory?

[bkonyi]

Not that I know of. Is it possible that you're cancelling the returned stream more than once?

[kenzieschmoll]

We listen to the same stream in multiple places in DevTools - does each call to onEventWithHistory return the same stream or a new instance?

[kenzieschmoll]

In DevTools we call .cancel() on the StreamSubscription object we create with stream.listen - we never actually cancel the stream itself.

[kenzieschmoll]

This is the leading crash right now. 30k+ exceptions in the last 7 days.

[bkonyi]

Can you reproduce locally?

[kenzieschmoll]

Yeah. Repro steps are to connect DevTools to a flutter app, then connect to a new app (click device info in bottom right of DevTools -> connect to new app).

[kenzieschmoll]

We listen to the stream using our auto_dispose code in DevTools. We then cancel the stream subscription on app disconnect:

devtools/packages/devtools_app/lib/src/auto_dispose.dart

Line 43 in 201e683

subscription.cancel();

. This is the first call to cancel(), making the call to cancel in dds throw the exception: https://github.com/dart-lang/sdk/blob/master/pkg/dds/lib/vm_service_extensions.dart#L94.

Should we not be cancelling our own stream subscription in DevTools for the streams with history? This seems counter-intuitive to how regular streams are handled. Should dds be checking if streamEvents is closed before calling cancel?

[bkonyi]

Oh awesome! Thanks for the details. I'll take a closer look today or tomorrow.

[bkonyi]

Fixed in package:dds 2.1.3. We just need to bump the version in DevTools now.