eclipse-theia/theia

Clicking "Continue" in debugger doesn't return to Running state

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#7,691 opened on Apr 29, 2020

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Description

I'm debugging an issue when running Flutter apps - when I resume from a breakpoint, the debugger UI often immediately goes back to the "paused" state so it looks like it has hit the breakpoint a second time when it hasn't.

I recorded the DAP traffic when this happens, and noticed there are stackTraceRequests also being sent immediately after resuming:


// Clicked Continue in debug side bar
[12:43:30 PM]: DAP-REQ: continueRequest: {"threadId":0}
[12:43:30 PM]: DAP-RESP: {"seq":0,"type":"response","request_seq":22,"command":"continue","success":true,"body":{"allThreadsContinued":false}}
// Debugger asks for stack traces, even though we're no longer paused
[12:43:31 PM]: DAP-REQ: stackTraceRequest: {"startFrame":0,"levels":1,"threadId":0}
[12:43:31 PM]: DAP-RESP: {"seq":0,"type":"response","request_seq":23,"command":"stackTrace","success":true,"body":{"stackFrames":[{"id":17,"source":{"name":"package:gitpod_flutter_web/main.dart","path":"/workspace/gitpod-flutter-web/lib/main.dart","sourceReference":0,"adapterData":{"type":"@Script","id":"353","uri":"package:gitpod_flutter_web/main.dart"}},"line":56,"column":7,"name":"<closure>"}],"totalFrames":15}}
[12:43:31 PM]: DAP-REQ: stackTraceRequest: {"startFrame":1,"levels":19,"threadId":0}
[12:43:31 PM]: DAP-RESP: {"seq":0,"type":"response","request_seq":24,"command":"stackTrace","success":false,"message":"-32603 Bad state: Invalid null response from service\n#0      VmServerConnection._delegateRequest (package:vm_service/src/vm_service.dart:1475:9)\n<asynchronous suspension>\n#1      _rootRunUnary (dart:async/zone.dart:1192:38)\n#2      _CustomZone.runUnary (dart:async/zone.dart:1085:19)\n#3      _CustomZone.runUnaryGuarded (dart:async/zone.dart:987:7)\n#4      _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:339:11)\n#5      _BufferingStreamSubscription._add (dart:async/stream_impl.dart:266:7)\n#6      _ForwardingStreamSubscription._add (dart:async/stream_pipe.dart:134:11)\n#7      _MapStream._handleData (dart:async/stream_pipe.dart:234:10)\n#8      _ForwardingStreamSubscription._handleData (dart:async/stream_pipe.dart:166:13)\n#9      _rootRunUnary (dart:async/zone.dart:1192:38)\n#10     _CustomZone.runUnary (dart:async/zone.dart:1085:19)\n#11     _CustomZone.runUnaryGuarded (dart:async/zone.dart:987:7)\n#12     _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:339:11)\n#13     _BufferingStreamSubscription._add (dart:async/stream_impl.dart:266:7)\n#14     _SyncStreamControllerDispatch._sendData (dart:async/stream_controller.dart:779:19)\n#15     _StreamController._add (dart:async/stream_controller.dart:655:7)\n#16     _StreamController.add (dart:async/stream_controller.dart:597:5)\n#17     new WebSocketImpl.fromSocket.<anonymous closure> (package:web_socket_channel/src/copy/web_socket_impl.dart:719:21)\n#18     _rootRunUnary (dart:async/zone.dart:1192:38)\n#19     _CustomZone.runUnary (dart:async/zone.dart:1085:19)\n#20     _CustomZone.runUnaryGuarded (dart:async/zone.dart:987:7)\n#21     _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:339:11)\n#22     _BufferingStreamSubscription._add (dart:async/stream_impl.dart:266:7)\n#23     _SinkTransformerStreamSubscription._add (dart:async/stream_transformers.dart:7…
[12:43:31 PM]: DAP-REQ: scopesRequest: {"frameId":17}
[12:43:31 PM]: DAP-RESP: {"seq":0,"type":"response","request_seq":25,"command":"scopes","success":true,"body":{"scopes":[{"name":"Locals","variablesReference":18,"expensive":false}]}}
[12:44:29 PM]: DAP-REQ: stackTraceRequest: {"startFrame":0,"levels":1,"threadId":0}
[12:44:29 PM]: DAP-RESP: {"seq":0,"type":"response","request_seq":26,"command":"stackTrace","success":false,"message":"No thread with id 0"}
[12:44:29 PM]: DAP-REQ: stackTraceRequest: {"startFrame":0,"levels":19,"threadId":0}
[12:44:29 PM]: DAP-RESP: {"seq":0,"type":"response","request_seq":27,"command":"stackTrace","success":false,"message":"No thread with id 0"}

I don't know whether the stackTraceRequests are causing the UI to go back to looking like it's paused, or whether the debugger thinks it's not paused which is why it's sending stackTraceRequests, but this seems unexpected.

Contributor guide

Tech stack
typescript
Domain
frontendtooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Debug Adapter Protocol (DAP)Asynchronous programmingTypeScript
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
25
Research direction
Investigate the debugger's DAP client implementation to understand why stackTraceRequests are sent after a continue response. Look at the handling of continue responses and the state machine that tracks paused/running state. The logs show that after continue response, stackTraceRequests are sent, which may cause the UI to revert to paused. Check the adapter code in theia/packages/debug/src/browser/debug frontend application.ts or similar. Ensure that after a continue request, any pending or subsequent stackTrace requests are ignored until the next breakpoint.