Pause command doesn't work

[renannprado]

After starting a debug session, if you hit pause button, nothing happens.
This is important if you want to add breakpoints after running the application.
I was debugging the plugin and saw that pauseRequest was never called. So I wonder whether this is a bug in this plugin or in the whole vscode.

[renannprado]

@ramya-rao-a is this an issue with the plugin or with vscode?
if it is a problem with the plugin, maybe I can try to help fix it

[ramya-rao-a]

I dont have a proper repro for this. Can you share a sample code with repro steps?

cc @roblourens

[renannprado]

So here are the steps to reproduce:

1. start the debugging session with no breakpoints
2. try to put a breakpoint (it won't work, the requests to create the breakpoint get stuck in delve)
   2.1. the only way to make the breakpoint to be created in that case would be if we send Halt to delve by clicking in pause button
3. click in the pause button and nothing happens...

Sample program

package main

import (
	"fmt"
	"sync"
	"time"
)

func main() {
	wg := &sync.WaitGroup{}

	wg.Add(1)

	go func() {
		for {
			fmt.Println("I'll just take a nap for a second... ZZZzz....")
			time.Sleep(time.Second)
		}
	}()

	wg.Wait()
}

[ramya-rao-a]

Thanks for the steps @renannprado

cc @roblourens

[roblourens]

When debugging starts, vscode sends a ThreadsRequest. goDebug.ts sends a ListGoroutines request to Delve, but Delve never responds. So then when you click Pause, vscode doesn't know which thread to pause, and never sends the pause request over. I suppose we need to figure out whether we're caling ListGoroutines at a bad time, whether it's a Delve bug, or if we should just add a timeout for it.

[roblourens]

And as for setting the bp after launch, I don't know whether it should be possible to set a BP when Go is in a loop like that. I can't do it with Delve at least.

[renannprado]

@roblourens yes, it is possible (will later update with an asciinema session to show)
the only way to set a breakpoint in this case would be to use the command Halt (using the pause button in vscode), then everything is paused on the process and you are free to set the breakpoints

[muravjov]

Hi, I searched why I cannot set breakpoints as verified in VSCode while the program is running (after continue) and found out that you cannot set breakpoints in delve until you stop/halt debuggee program via delve.

That is, if you try to set a breakpoint in vscode while the debuggee program runs, the request to delve CreateBreakpoint hangs forever (till debugging session' end) and even F6 (Pause) will not work.
Workaround: before setting breakpoint you hit F6 (Pause), then set breakpoint, then Continue (F5) and everything is ok.

So I suggest to make start/stop requests to delve for every breakpoint being set if debuggee is running. That is, to call pauseRequest()/continueRequest() in setBreakPointsRequest() , see at

https://github.com/Microsoft/vscode-go/blob/master/src/debugAdapter/goDebug.ts#L530

---

I've checked out Goland, https://www.jetbrains.com/go/ , and found out that they do just stop/start in such situations. Here is the log from delve (patched by me) under Goland control, showing that delve was started and stopped only for setting breakpoint:

2018/01/27 23:44:22 server.go:265: rpc command: RPCServer.Command, version 2
2018/01/27 23:44:22 server.go:292: rpc command, is sync: false
2018/01/27 23:44:22 debugger.go:490: Debugger.Command: start
2018/01/27 23:44:22 debugger.go:498: halting
2018/01/27 23:44:23 debugger.go:562: Debugger.Command: stop
2018/01/27 23:44:23 debugger.go:562: Debugger.Command: stop
2018/01/27 23:44:23 server.go:265: rpc command: RPCServer.CreateBreakpoint, version 2
2018/01/27 23:44:23 server.go:292: rpc command, is sync: true
2018/01/27 23:44:23 debugger.go:284: CreateBreakpoint: 1
2018/01/27 23:44:23 debugger.go:303: CreateBreakpoint: 2
2018/01/27 23:44:23 debugger.go:328: CreateBreakpoint: 3
2018/01/27 23:44:23 debugger.go:339: CreateBreakpoint: 4
2018/01/27 23:44:23 debugger.go:348: created breakpoint: &api.Breakpoint{ID:1, Name:"", Addr:0x8b8188, File:"/home/ilya/opt/programming/g-core/balancer/src/balancer/master.go", Line:95, FunctionName:"balancer.SendCommandTo", Cond:"", Tracepoint:false, Goroutine:false, Stacktrace:0, Variables:[]string(nil), LoadArgs:(*api.LoadConfig)(nil), LoadLocals:(*api.LoadConfig)(nil), HitCount:map[string]uint64{}, TotalHitCount:0x0}
2018/01/27 23:44:23 server.go:265: rpc command: RPCServer.Command, version 2
2018/01/27 23:44:23 server.go:292: rpc command, is sync: false
2018/01/27 23:44:23 debugger.go:490: Debugger.Command: start
2018/01/27 23:44:23 debugger.go:509: continuing

Also, I've checked https://github.com/derekparker/delve sources and found out why one should not request CreateBreakpoint command while debuggee is working: every command except halt (= Pause in vscode) try to lock processMutex before performing its action, but if it is already locked (while debuggee runs) so the request hangs forever:

// CreateBreakpoint creates a breakpoint.
func (d *Debugger) CreateBreakpoint(requestedBp *api.Breakpoint) (*api.Breakpoint, error) {
	d.processMutex.Lock()
	defer d.processMutex.Unlock()
...

See at https://github.com/derekparker/delve/blob/master/service/debugger/debugger.go#L284

[muravjov]

I am not so good with TypeScript and those promises so I cannot make PR for my suggestion myself, the right way. Please help me with that.

[ramya-rao-a]

@muravjov Thanks for the investigation!

So I suggest to make start/stop requests to delve for every breakpoint being set if debuggee is running. That is, to call pauseRequest()/continueRequest() in setBreakPointsRequest()

This would work assuming that pauseRequest() itself works as expected and halts delve.
As @renannprado and @roblourens has discussed above, that doesnt seem to be happening.
Are you able to pause the program and then set breakpoints?