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[flutter_tools] Fix deadlock in debug adapters when process exits early - #190931
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When launching a debug session, if the process exits before the debugger connects, the debug adapter would deadlock waiting for the debugger to initialize. This change sets `waitingForDebugger = true` before launching the process, and uses `Future.any` to wait for either `debuggerInitialized` or `debuggerInitializationFailedCompleter.future`. The completer is completed with an error when the session terminates, breaking the deadlock. Fixes flutter#190721
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This pull request updates the Flutter debug adapters to handle early session termination during debugger initialization by introducing a debuggerInitializationFailedCompleter and a waitingForDebugger flag, allowing the adapter to fail fast if the process exits early. The review feedback identifies a potential unhandled asynchronous exception if the completer is completed with an error before listeners are attached, and points out that the new public fields lack required documentation.
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| bool waitingForDebugger = false; | ||
| final Completer<void> debuggerInitializationFailedCompleter = Completer<void>(); |
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Issue: Potential Unhandled Asynchronous Exception & Missing Documentation
-
Unhandled Exception Risk: If
handleSessionTerminateis called whilelaunchAsProcessis running (wherewaitingForDebuggeristruebutFuture.anyhas not yet been awaited),debuggerInitializationFailedCompleter.completeErrorwill be called. Since there are no listeners ondebuggerInitializationFailedCompleter.futureat that moment, this will result in an unhandled asynchronous exception in Dart, which can crash the process or cause test flakiness.Adding a dummy error handler using
..future.catchError((Object _) {})at creation time safely prevents unhandled exceptions while still allowingFuture.anyto receive the error when it eventually listens to it. -
Missing Documentation: According to the Repository Style Guide (Line 62: "All public members should have documentation."), these new public fields should have
///doc comments explaining their purpose.
Here is the suggested improvement:
/// Whether the adapter is currently waiting for the debugger to initialize.
bool waitingForDebugger = false;
/// A completer that completes with an error if debugger initialization fails
/// (for example, if the session terminates early).
///
/// A dummy error handler is attached to the future to prevent unhandled
/// asynchronous exceptions if it completes before any listeners are active.
final Completer<void> debuggerInitializationFailedCompleter = Completer<void>()
..future.catchError((Object _) {});References
- All public members should have documentation. (link)
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Did the bot get smart?
I think it's right - flutter_test_adapter sets waitingForDebugger = true before an await, so if it happens before reading the Future.any(), there will be no listeners and this might be an unhandled error?
…initialization failure and document public members
DanTup
approved these changes
Aug 11, 2026
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autosubmit label was removed for flutter/flutter/190931, because - The status or check suite Dashboard Checks has failed. Please fix the issues identified (or deflake) before re-applying this label. |
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autosubmit label was removed for flutter/flutter/190931, because - The status or check suite Dashboard Checks has failed. Please fix the issues identified (or deflake) before re-applying this label. |
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…#12453) Manual roll Flutter from 27b098811f3b to c2437523d308 (179 revisions) Manual roll requested by tarrinneal@google.com flutter/flutter@27b0988...c243752 2026-08-12 matt.boetger@gmail.com Enable Gradle CI cache on all test targets that require android_sdk (flutter/flutter#190723) 2026-08-12 bkonyi@google.com [analysis] Reland "Added initial implementation of the flutter_analyzer_plugin (#175679)" (flutter/flutter#191022) 2026-08-12 matt.boetger@gmail.com Switch testing to gradle bin distribution type instead of all (flutter/flutter#190738) 2026-08-12 matt.boetger@gmail.com Convert Mockito instances in Kotlin to Mockk (flutter/flutter#189884) 2026-08-12 chingjun@google.com Report individual test results to LUCI ResultDB (flutter/flutter#190254) 2026-08-12 victorsanniay@gmail.com Toggleable reaction duration respects overrides (flutter/flutter#190857) 2026-08-12 engine-flutter-autoroll@skia.org Roll Skia from e00dbd7448c4 to fee7272f5bc2 (1 revision) (flutter/flutter#191007) 2026-08-12 30870216+gaaclarke@users.noreply.github.com Started caching text shadows by content. 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When launching a debug session, if the target process exited early (e.g., due to a startup error, non-existent target, or failure before the VM service connects), the debug adapter would deadlock waiting indefinitely for
debuggerInitializedto complete.This change:
waitingForDebuggerand adds adebuggerInitializationFailedCompleterinFlutterBaseDebugAdapter.debuggerInitializationFailedCompleterwith aDebugAdapterExceptioninhandleSessionTerminateifwaitingForDebuggeris active.FlutterTestDebugAdapter.launchImplandFlutterDebugAdapter._handleAppStarted, racesdebuggerInitializedagainstdebuggerInitializationFailedCompleter.futureviaFuture.any, allowing the adapter to fail fast and terminate cleanly without hanging.Fixes #190721
Pre-launch Checklist
///).