Debugger doesn't work for processes which fork other processes

[medikoo]

I'm running:

$ node --inspect some-node-script.js

Where some-node-script.js uses plain child_process.fork (run with defaults mostly) calls to initialize few other processes internally. Right after that I receive message Unable to open devtools socket: address already in use:

$ node -v
v7.0.0
$ node --inspect some-node-script.js
Debugger listening on port 9229.
Warning: This is an experimental feature and could change at any time.
To start debugging, open the following URL in Chrome:
    chrome-devtools://devtools/remote/serve_file/@60cd6e859b9f557d2312f5bf532f6aec5f284980/inspector.html?experiments=true&v8only=true&ws=localhost:9229/edbce9e9-0a9d-4c24-8f2b-bcaaeb4a5965
Unable to open devtools socket: address already in use

Also forked process crashes so technically application doesn't run (I've skipped that part of a log to avoid not related noise).

Behavior is same in both latest Node.js v7 and v6 (Tested on OSX, both El Captain and Sierra, with latest Chrome on board)

Am I doing something wrong, or there's no support currently for multi-process Node.js apps?

I've found similar issue which states that this probably should just work, but gives no clue why it actually doesn't.

I'll be happy to provide simple test case if needed

[mscdex]

/cc @nodejs/v8-inspector

[bnoordhuis]

I've found similar issue which states that this probably should just work, but gives no clue why it actually doesn't.

child_process.fork() doesn't fix up execArgv, only cluster.fork() does. See #8495 (comment).

[medikoo]

child_process.fork() doesn't fix up execArgv, only cluster.fork() does. See #8495 (comment).

Thanks, that clearer now. Is there a plan to fix it for child_process.fork?

[medikoo]

After reading this comment I see that probably #5025 is meant to fix this issue

[bmeck]

with v8 landing RemoteExecutionContext, it should be possible for a debugger to work for multiple processes. I don't know if we are ready for that and it requires v8 version >=55 which isn't going to land on Node v6

[eugeneo]

V8 inspector protocol has support for the "subtargets" - we are currently
looking into leveraging that for the node processes that fork children.
#9630 updates the HTTP transport for the
inspector, now it should be able to track multiple "sessions" and also list
multiple targets.

Currently we are considering introducing a special "inspector" pipe from
the parent to a child so the child does not have to run the HTTP server.
All communications with the children will happen through the parent, parent
will also be able to list individual children.

Note that this work is in experimental stage and the design will likely
change a lot.

On Thu, Nov 17, 2016 at 1:21 PM Bradley Meck notifications@github.com
wrote:

with v8 landing RemoteExecutionContext, it should be possible for a
debugger to work for multiple processes. I don't know if we are ready for
that and it requires v8 version >=55 which isn't going to land on Node v6

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[Trott]

@eugeneo Should this remain open?

[eugeneo]

I believe it can be closed.