Allow attaching to a process without pausing the execution

[dlsniper]

Sorry, the issue was created too fast :D
Proper description:
Given the following app:

package main

import (
    "fmt"
    "net/http"
)

func handler(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintln(w, "hello")
}

func main() {

    handlers := http.NewServeMux()
    handlers.HandleFunc("/", handler)
    server := &http.Server{Addr: ":8889", Handler: handlers}

    server.ListenAndServe()
}

When I'm doing the following steps:

go build -gcflags "-N -l" -o demo demo.go
./demo &
dlv attach `pgrep demo`

I can observe a pause in execution until I send the continue command to the debugger.

While I do understand that it might be useful to have that functionality, say for example I want to hook up in a staging app that has traffic on it (sample traffic), attaching to its process and having it paused is not ideal (for example I want to set tracepoints rather that breakpoints).

Do you think it would be useful to have an attach --no-pause flag?

[derekparker]

I can't see the value of starting an actual debug session without pausing unless you're simply relying on providing an init file (to load breakpoints / tracepoints) and then want to immediately continue execution, which you could do by writing a continue command at the end of the init file.

You can already set tracepoints without stopping the program indefinitely with the trace subcommand, which takes a pid flag.

[luisgarciaalanis]

@derekparker I run the code in a docker container and remote debug. So for normal development its nice to auto run, then I could click the play button on VSCODE to attach, add a breakpoint and rerun to hit the breakpoint.

it would be quite convinient to be able to do this.

[luisgarciaalanis]

reflex -s -r '.go$' -- dlv --listen=:5432 debug --headless=true --init <(printf continue)
this does not auto continue :(

[aarzilli]

Closed by 9a21621

[dlsniper]

@aarzilli I read the changelog of the commit that closed this but I'm not sure how to use delve to do it (and I haven't tried it yet either). Is the original reported case possible now? Thank you.

[aarzilli]

--init <(echo continue) does it for normal instances (that don't have the --headless flag). For headless instances invoke dlv a second time like this: dlv --init <(echo "exit -c") connect ...

[gm42]

In case of --headless the --init gets ignored with the following message in output:

Warning: init file ignored

Thus a separate client connection is needed to start the process; this is not container friendly and some hack is needed to trigger the operation externally.

[hypnoce]

I'm not sure if this problem is solved, but in some scenarios it can be nice to start a go binary with delve without pausing the execution, like running java with suspend=n.
Do you see any value into this ?

[derekparker]

I'm going to reopen this as it technically is not fixed, we currently just support a workaround.

[briandealwis]

Having a no-suspend option is useful for debugging go-based microservices in containers.