Node child forks can't use the debugger

[romainbessugesmeusy]

Hi Jos,

It looks like I can't use node debugger while spawning child processes, because each worker try to use the same port. Example:

Debugger listening on 127.0.0.1:51884
Error: listen EADDRINUSE 127.0.0.1:51884
    at Object.exports._errnoException (util.js:1023:11)
    at exports._exceptionWithHostPort (util.js:1046:20)
    at Agent.Server._listen2 (net.js:1261:14)
    at listen (net.js:1297:10)
    at doListening (net.js:1396:7)
    at _combinedTickCallback (internal/process/next_tick.js:77:11)
    at process._tickCallback (internal/process/next_tick.js:98:9)

It seems that child forks have to be created with the --debugger={port}. My first guess would be to change this line (WorkerHandler.js:79):

    this.worker = node.require('child_process').fork(this.script);

What do you think?

Thanks again for your work, cheers from France

[romainbessugesmeusy]

I think it's interesting to mention this discussion on the IntelliJ / WebStorm board

https://intellij-support.jetbrains.com/hc/en-us/community/posts/206193339-Debugging-node-child-processes

[josdejong]

Thanks for reporting Romain!

It seems that child forks have to be created with the --debugger={port}

Wouldn't that always run the childs in debug mode, also if you just want to run in production?

[romainbessugesmeusy]

Yeah I fear you're right. Furthermore I haven't found yet how to attach a remote debugger to child process inside Webstorm... Maybe this could be passed when creating the pool, as a secondary argument.

var workerpool = require('workerpool');

// create a worker pool using an external worker script
var pool = workerpool.pool(__dirname + '/myWorker.js', {
   node: {
       childProcessExecArgs: (childIndex) => return '--debugger=' + (53027 + childIndex)
   }
});

[josdejong]

hm that's odd. I can hardly believe we're the first stumbling upon this problem.

Maybe we could check whether the --debugger option is in the arguments of the main process, and only then add it in the childProcessExecArgs with a unique port. Or is that what you mean?

From the thead you mentioned I understand that it should be enough to pass an argument --debug-brk which will let node.js automatically pick a free port.

Oh, it could be simplified in the following way (forgot to mention it in the first place):

var childProc= fork('./public/LG/lg.js',{execArgv: ['--debug-brk']})

In that case node automatically finds a free port.

@romainbessugesmeusy would you be interested in doing some experimenting with this to find a working solution for workerpool?

[romainbessugesmeusy]

Yeah I'll look into that 👌

[josdejong]

👍

[josdejong]

@romainbessugesmeusy did you already found some time to look into the debugging issue?

[josdejong]

This issue should have been fixed now in v2.2.1 (see #21)