Listening to SIGUSR1 blocks debugger

[mlucool]

• Version: v8.9.4
• Platform: 3.10.0-693.17.1.el7.x86_64

I am not sure which is the correct behavior for an intercepted SIGUSR1, the documentation or the a test case. Can the code and/or documentation please be fixed?

process documentation says:

SIGUSR1 is reserved by Node.js to start the debugger. It's possible to install a listener but doing so will not stop the debugger from starting.

But a quick test shows that the debugger is not started.

Code:

let i = 0;
setInterval(() =>
        console.log(i++),
    1000);

process.on('SIGUSR1', () => console.log('Got SIGUSR1'))

If you send a SIGUSR1 only Got SIGUSR1 is printed. The typical Debugger listening on ws://127.0.0.1:9229/66fb119d-2443-4bdf-80b1-6386995ba253 is not printed. You can also verify that the debugger didn't start with with netstat -ap.

[targos]

@nodejs/v8-inspector

[bnoordhuis]

It depends on when the inspector is started. If it's activated at startup, then the JS code will override it. If it's activated later, it subsumes the JS listener.

I think right now it's always started early (require('inspector').open() uses a different mechanism) but it hasn't always been that way and it could change again in the future.

I'd use guarded language: "It's possible to install a listener but doing so might interfere with the debugger."

[willhayslett]

@bnoordhuis please let me know if the changes are okay or if additional edits are needed. Thanks.

[mlucool]

@bnoordhuis Do you expect this to always work/enable me to set the port at runtime?

process.on('SIGUSR1', () => {
    const port = myPortFinder();
    require('inspector').open(port);
});