Debugger: Failed to debug Xunit project when start debugging again

[GraceDong]

Environment data

dotnet --info output:

• OS Name: debain
• OS Version: 8
• OS Platform: Linux
• RID: debian.8-x64
• Base Path: /opt/dotnet/sdk/1.0.1

VS Code version: v1.11.2
C# Extension version: v1.9.0

Steps to reproduce

1. Open attached folder with VSCode.
   test-xunit.zip
2. Set a breakpoint at the line of 11 in UnitTest1.cs;
3. Debug test;
4. Debug test again

Expected behavior

Re-start debugging and the breakpoint should be hit again.

Actual behavior

Pop a error message as following:

Log: log.txt

[DustinCampbell]

@GraceDong: Any chance you could provide the OmniSharp log when this happens? You can get it by selecting View- >Output and then choosing "OmniSharp Log" from the top-right corner of the Output pane.

[DustinCampbell]

OK. I'm able to reproduce this on Debian 8. For me, it happens if perform the following task a few times in a row:

1. Click "debug test"
2. Hit breakpoint
3. Press stop to end the debugging session.

Eventually, the debugger seems to get into a weird state and the debugger events never fire. That leaves OmniSharp in a bad state, which results in the "Failed to start debugger: null" message.

Below is the content of the .NET Test Log output channel from a reproduction of the issue. Note that there were three successful runs and then the debugger didn't reported that it had started the debugging process on the fourth run.

Debugging method 'test_xunit.UnitTest1.Test1'.
Started debugging process #6102.
[xUnit.net 00:00:01.7993819]   Starting:    test-xunit
The active test run was aborted. Reason: Unable to communicate with test host process.
Debugging complete.

Debugging method 'test_xunit.UnitTest1.Test1'.
Started debugging process #6269.
[xUnit.net 00:00:01.7056933]   Starting:    test-xunit
The active test run was aborted. Reason: Unable to communicate with test host process.
Debugging complete.

Debugging method 'test_xunit.UnitTest1.Test1'.
Started debugging process #6407.
[xUnit.net 00:00:01.6709782]   Starting:    test-xunit
The active test run was aborted. Reason: Unable to communicate with test host process.
Debugging complete.

Debugging method 'test_xunit.UnitTest1.Test1'.
Debugging method 'test_xunit.UnitTest1.Test1'.

Here's an OmniSharp log at this point. Note that there are a few successful test debugging sessions and then it gets horked:

[info]: OmniSharp.DotNetTest.VSTestManager
        read: {"MessageType":"TestSession.Connected","Payload":null}
[info]: OmniSharp.DotNetTest.VSTestManager
        read: {"MessageType":"ProtocolVersion","Payload":1}
[info]: OmniSharp.DotNetTest.DebugSessionManager
        Debug session started.
[info]: OmniSharp.DotNetTest.DebugSessionManager
        Debug session ended.
[info]: OmniSharp.DotNetTest.VSTestManager
        read: {"MessageType":"TestSession.Connected","Payload":null}
[info]: OmniSharp.DotNetTest.VSTestManager
        read: {"MessageType":"ProtocolVersion","Payload":1}
[info]: OmniSharp.DotNetTest.DebugSessionManager
        Debug session started.
[info]: OmniSharp.DotNetTest.DebugSessionManager
        Debug session ended.
[info]: OmniSharp.DotNetTest.VSTestManager
        read: {"MessageType":"TestSession.Connected","Payload":null}
[info]: OmniSharp.DotNetTest.VSTestManager
        read: {"MessageType":"ProtocolVersion","Payload":1}
[info]: OmniSharp.DotNetTest.DebugSessionManager
        Debug session started.
[info]: OmniSharp.DotNetTest.DebugSessionManager
        Debug session ended.
[info]: OmniSharp.DotNetTest.VSTestManager
        read: {"MessageType":"TestSession.Connected","Payload":null}
[info]: OmniSharp.DotNetTest.VSTestManager
        read: {"MessageType":"ProtocolVersion","Payload":1}
[info]: OmniSharp.DotNetTest.DebugSessionManager
        Debug session started.
[info]: OmniSharp.DotNetTest.VSTestManager
        read: {"MessageType":"TestSession.Connected","Payload":null}
[info]: OmniSharp.DotNetTest.VSTestManager
        read: {"MessageType":"ProtocolVersion","Payload":1}
[fail]: OmniSharp.DotNetTest.DebugSessionManager
        Debug session not started.
[fail]: Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware
        An unhandled exception has occurred: Debug session already started.
System.InvalidOperationException: Debug session already started.
  at OmniSharp.DotNetTest.DebugSessionManager.VerifySession (System.Boolean isStarted) [0x00055] in <7124f501081e464b97067a98f0b0e806>:0 
  at OmniSharp.DotNetTest.DebugSessionManager.StartSession (OmniSharp.DotNetTest.TestManager testManager) [0x00011] in <7124f501081e464b97067a98f0b0e806>:0 
  at OmniSharp.DotNetTest.Services.DebugTestService.Handle (OmniSharp.DotNetTest.Models.DebugTestGetStartInfoRequest request) [0x0000d] in <7124f501081e464b97067a98f0b0e806>:0 
  at OmniSharp.Middleware.Endpoint.Exports.RequestHandlerExportHandler`2[TRequest,TResponse].Handle (TRequest request) [0x00000] in <30afbacdd97f44c59c542cdbc3e6fa9a>:0 
  at OmniSharp.Middleware.Endpoint.EndpointHandler`2+<HandleSingleRequest>d__18[TRequest,TResponse].MoveNext () [0x00092] in <30afbacdd97f44c59c542cdbc3e6fa9a>:0 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <12e050e5b3d34326a1b4e2e7624e75da>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0004e] in <12e050e5b3d34326a1b4e2e7624e75da>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in <12e050e5b3d34326a1b4e2e7624e75da>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in <12e050e5b3d34326a1b4e2e7624e75da>:0 
  at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in <12e050e5b3d34326a1b4e2e7624e75da>:0 
  at OmniSharp.Middleware.Endpoint.EndpointHandler`2+<Process>d__16[TRequest,TResponse].MoveNext () [0x0025e] in <30afbacdd97f44c59c542cdbc3e6fa9a>:0 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <12e050e5b3d34326a1b4e2e7624e75da>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0004e] in <12e050e5b3d34326a1b4e2e7624e75da>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in <12e050e5b3d34326a1b4e2e7624e75da>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in <12e050e5b3d34326a1b4e2e7624e75da>:0 
  at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in <12e050e5b3d34326a1b4e2e7624e75da>:0 
  at OmniSharp.Middleware.EndpointMiddleware+<Invoke>d__7.MoveNext () [0x000d8] in <30afbacdd97f44c59c542cdbc3e6fa9a>:0 
--- End of stack trace from previous location where exception was thrown ---
  at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in <12e050e5b3d34326a1b4e2e7624e75da>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0004e] in <12e050e5b3d34326a1b4e2e7624e75da>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in <12e050e5b3d34326a1b4e2e7624e75da>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in <12e050e5b3d34326a1b4e2e7624e75da>:0 
  at System.Runtime.CompilerServices.TaskAwaiter.GetResult () [0x00000] in <12e050e5b3d34326a1b4e2e7624e75da>:0 
  at Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware+<Invoke>d__6.MoveNext () [0x00080] in <54abb6e5c34d41e5b18eb3ce35092c5b>:0

[DustinCampbell]

Fixed with #1417.