System.NullReferenceException when continuing after adding breakpoint.

Bug type: Debugger

Describe the bug

• OS and Version: Linux (arm64 and x86_64), gdb 9.2 (NOTE: does not reproduce on macOS with lldb)
• VS Code Version: vimspector
• C/C++ Extension Version: 1.9.7
• Other extensions you installed (and if the issue persists after disabling them): N/A
• A clear and concise description of what the bug is.

After upgrading vimspector to 1.9.7 vscode-cpptools I’m getting regression test failures. The first one I have diagnosed as a MIEngine exception.

To Reproduce

There appears to be timing involved because manual steps do not reproduce, however my automated tests fail reliably. The test in question does this:

1. Open this file: https://github.com/puremourning/vimspector/blob/master/tests/testdata/cpp/simple/simple.cpp
2. Start debugging with stopAtEntry true
3. Execution pauses at line 15
4. Set a breakpoint at line 16 and ensure it goes ‘VERIFIED’
5. Delete the breakpoint
6. add it again
7. Continue execution
8. Expect a stopped event on line 16.

However on both linux x86_64 and linux arm64, I get the following Unable to continue. Operation failed with error code 0x80004004 preceded by ERROR: Internal error in MIEngine. Exception of type 'System.NullReferenceException' was thrown.

2022-03-26 14:09:32,834 - DEBUG - Sending Message: {"command": "setBreakpoints", "arguments": {"source": {"name": "simple.cpp", "path": "/home/dev/vimspector/tests/testdata/cpp/simple/simple.cpp"}, "breakpoints": [{"line": 16}], "sourceModified": false}, "seq": 18, "type": "request"}
2022-03-26 14:09:32,834 - DEBUG - Sending Message: {"command": "setFunctionBreakpoints", "arguments": {"breakpoints": []}, "seq": 19, "type": "request"}
2022-03-26 14:09:32,835 - DEBUG - Sending Message: {"command": "setExceptionBreakpoints", "arguments": {"filters": []}, "seq": 20, "type": "request"}
2022-03-26 14:09:32,847 - DEBUG - Message received: {'type': 'response', 'request_seq': 18, 'success': True, 'command': 'setBreakpoints', 'body': {'breakpoints': [{'id': 2, 'verified': True, 'line': 16, 'BoundBreakpoints': []}]}, 'seq': 41}
2022-03-26 14:09:32,847 - DEBUG - Message received: {'type': 'event', 'event': 'breakpoint', 'body': {'reason': 'changed', 'breakpoint': {'id': 2, 'verified': True, 'line': 16, 'BoundBreakpoints': []}}, 'seq': 42}
2022-03-26 14:09:32,848 - DEBUG - Message received: {'type': 'response', 'request_seq': 19, 'success': True, 'command': 'setFunctionBreakpoints', 'body': {'breakpoints': []}, 'seq': 43}
2022-03-26 14:09:32,848 - DEBUG - Message received: {'type': 'response', 'request_seq': 20, 'success': True, 'command': 'setExceptionBreakpoints', 'body': {}, 'seq': 44}
2022-03-26 14:09:32,849 - DEBUG - Sending Message: {"command": "continue", "arguments": {"threadId": 416}, "seq": 21, "type": "request"}
2022-03-26 14:09:32,884 - DEBUG - Message received: {'type': 'event', 'event': 'output', 'body': {'category': 'stderr', 'output': "ERROR: Internal error in MIEngine. Exception of type 'System.NullReferenceException' was thrown.\r\n\r\n   at Microsoft.MIDebugEngine.DebuggedProcess.Execute(DebuggedThread thread)\n   at Microsoft.MIDebugEngine.WorkerThread.TrySetOperationInternal(Delegate op)\n   at Microsoft.MIDebugEngine.WorkerThread.SetOperationInternal(Delegate op)\n   at Microsoft.MIDebugEngine.WorkerThread.RunOperation(AsyncOperation op)\n   at Microsoft.MIDebugEngine.AD7Engine.Continue(IDebugThread2 pThread)\n"}, 'seq': 45}
2022-03-26 14:09:32,887 - DEBUG - Message received: {'type': 'response', 'request_seq': 21, 'success': False, 'command': 'continue', 'message': 'Unable to continue. Operation failed with error code 0x80004004.', 'body': {}, 'seq': 46}
2022-03-26 14:09:32,888 - ERROR - Request failed (unhandled): Unable to continue. Operation failed with error code 0x80004004.

the configuration being used is captured in the initialise and launch requests:

2022-03-26 14:09:21,136 - DEBUG - Sending Message: {"command": "initialize", "arguments": {"adapterID": "cppdbg", "clientID": "vimspector", "clientName": "vimspector", "linesStartAt1": true, "columnsStartAt1": true, "locale": "en_GB", "pathFormat": "path", "supportsVariableType": true, "supp
ortsVariablePaging": false, "supportsRunInTerminalRequest": true, "supportsMemoryReferences": true}, "seq": 0, "type": "request"}
2022-03-26 14:09:21,791 - DEBUG - Message received: {'type': 'response', 'request_seq': 0, 'success': True, 'command': 'initialize', 'body': {'supportsConfigurationDoneRequest': True, 'supportsFunctionBreakpoints': True, 'supportsConditionalBreakpoints': True, 'supportsEvaluateForHovers': Tr
ue, 'exceptionBreakpointFilters': [{'filter': 'all', 'label': 'All C++ Exceptions', 'default': False, 'supportsCondition': True, 'conditionDescription': 'std::out_of_range,std::invalid_argument'}], 'supportsSetVariable': True, 'supportsGotoTargetsRequest': True, 'supportsCompletionsRequest':
 True, 'completionTriggerCharacters': [], 'supportsModulesRequest': True, 'supportedChecksumAlgorithms': [], 'supportsValueFormattingOptions': True, 'supportsLogPoints': True, 'supportsDataBreakpoints': True, 'supportsReadMemoryRequest': True, 'supportsDisassembleRequest': True, 'supportsCli
pboardContext': True, 'supportsSteppingGranularity': True, 'supportsInstructionBreakpoints': True, 'supportsExceptionFilterOptions': True}, 'seq': 1}
2022-03-26 14:09:21,791 - DEBUG - Sending Message: {"command": "launch", "arguments": {"args": [], "cwd": "/home/dev/vimspector/tests/testdata/cpp/simple", "environment": [], "type": "cppdbg", "targetArchitecture": "x86_64", "request": "launch", "program": "/home/dev/vimspector/tests/testdat
a/cpp/simple/simple", "externalConsole": false, "stopAtEntry": true, "stopOnEntry": true, "MIMode": "gdb", "name": "test"}, "seq": 1, "type": "request"}

Additional context

Gist of the full vimspector log which includes DAP trace with the engine Logging is here: https://gist.github.com/puremourning/f52268564824edbdf6779307ce1b88b0

[puremourning]

Great. Thanks for looking into it.

[WardenGnaw]

@puremourning Thanks for reporting this issue! Looks like a lucky timing issue that was caught by your tests.