debug: evaluating an expression while target is running blocks delve and the debug session

[polinasok]

Steps to reproduce:

1. Program

func main() {
	for i := 0; true; i++ {
		fmt.Println("================== i", i)
		time.Sleep(2 * time.Second)
	}
}

2. Launch debug session with "stopOnEntry":true
3. Click "Continue" (F5)
4. Evaluate any expression via Debug Console (e.g. 2+2)
5. Try to pause - it will not work

Log shows:

From client: continue({"threadId":1})
ContinueRequest
To client: {"seq":0,"type":"response","request_seq":9,"command":"continue","success":true}
ContinueResponse
2020-10-09T08:27:52-07:00 debug layer=rpc (async 13) <- RPCServer.Command(api.DebuggerCommand{"name":"continue","ReturnInfoLoadConfig":null})
2020-10-09T08:27:52-07:00 debug layer=debugger continuing
================== i 0
================== i 1
================== i 2
2+2
From client: evaluate({"expression":"2+2","context":"repl"})
EvaluateRequest
2020-10-09T08:28:03-07:00 debug layer=rpc <- RPCServer.Eval(rpc2.EvalIn{"Scope":{"GoroutineID":-1,"Frame":0,"DeferredCall":0},"Expr":"2+2","Cfg":{"FollowPointers":true,"MaxVariableRecurse":1,"MaxStringLen":64,"MaxArrayValues":64,"MaxStructFields":-1}}) <===== BLOCKING
================== i 3
================== i 4
From client: pause({"threadId":1})
PauseRequest
To client: {"seq":0,"type":"response","request_seq":11,"command":"pause","success":true}
PauseResponse <=============== NOT WORKING
================== i 5
================== i 6
From client: pause({"threadId":1})
PauseRequest
To client: {"seq":0,"type":"response","request_seq":12,"command":"pause","success":true}
PauseResponse  <=============== NOT WORKING
From client: disconnect({"restart":false})
DisconnectRequest
HaltRequest  <=============== BLOCKED
================== i 7
Killing debug process manually as we could not halt delve in time
killing debugee (pid: 32107)...
DisconnectRequest to parent
To client: {"seq":0,"type":"response","request_seq":13,"command":"disconnect","success":true}
DisconnectResponse

A call to getDebugState can be used before a call to delve is made to determine if it is running. In that case we can return an error that evaluation of expression is only supported when stopped.

[polinasok]

This has been addressed in the new dlv-dap adapter. The pause PR is still pending, but testing this with just disconnect, it is clear that delve is not blocked after getting an expression when running.

================== i 0
================== i 1
2+2
Unable to process `evaluate`: debuggee is running
================== i 2
Detaching and terminating target process
dlv dap (45444) exited with code: 0

With logging on:

8:39:22-07:00 debug layer=debugger continuing
================== i 0
================== i 1
================== i 2
2+2
2021-05-13T18:39:26-07:00 debug layer=dap [<- from client]{"seq":11,"type":"request","command":"evaluate","arguments":{"expression":"2+2","context":"repl","format":{}}}
2021-05-13T18:39:26-07:00 debug layer=dap Unable to process `evaluate`: debuggee is running
2021-05-13T18:39:26-07:00 debug layer=dap [-> to client]{"seq":0,"type":"response","request_seq":11,"success":false,"command":"evaluate","message":"Unable to process `evaluate`","body":{"error":{"id":4000,"format":"Unable to process `evaluate`: debuggee is running"}}}
Unable to process `evaluate`: debuggee is running
2021-05-13T18:39:28-07:00 debug layer=dap [<- from client]{"seq":12,"type":"request","command":"disconnect","arguments":{"terminateDebuggee":true}}
2021-05-13T18:39:28-07:00 debug layer=debugger halting
2021-05-13T18:39:28-07:00 debug layer=dap "continue" command stopped - reason "manual"
2021-05-13T18:39:28-07:00 debug layer=dap [-> to client]{"seq":0,"type":"event","event":"stopped","body":{"reason":"pause","allThreadsStopped":true}}
Detaching and terminating target process
2021-05-13T18:39:28-07:00 debug layer=dap [-> to client]{"seq":0,"type":"event","event":"output","body":{"category":"console","output":"Detaching and terminating target process\n","source":{}}}
2021-05-13T18:39:28-07:00 debug layer=debugger detaching
2021-05-13T18:39:28-07:00 debug layer=dap [-> to client]{"seq":0,"type":"response","request_seq":12,"success":true,"command":"disconnect"}
2021-05-13T18:39:28-07:00 debug layer=dap DAP server stopping...
2021-05-13T18:39:28-07:00 debug layer=dap DAP server stopped
dlv dap (42672) exited with code: 0