Node child process, channel closed on process.send

Question

Inside my worker file I listen for a data callback. someLib is node-serialport.

process.on('message', function(msg) {
    someLib.on('data', function(data){
        console.log('some data');
        process.send(data);
    });
});

This prints

some data
Error: channel closed

But

process.on('message', function(msg) {
    process.send('foobar');
});

works fine. It is strange but sometimes the first code example works, so the channel closed error appears randomly.

From http://nodejs.org/api/child_process.html#child_process_event_error I get the info that the error is triggered when

Sending a message to the child process failed for whatever reason.

What is "whatever reason"? Any ideas?

Emaemaciate

Answer 1

The problem was that forked child processes were not closed correctly when parent was killed. This resulted in multiple ghost processes that caused the channel closed error.

I hooked into the SIGHUP and killed them gracefully. Now everything works.

Emaemaciate

Answer 2

You need to specify the event type, since with process.send(data) you're just sending an object.

Frobisher

What type? According to nodejs.org/api/… there does not need to be a type – Emaemaciate

Yes, but in your code you're registering an event listener every time a message is received. I think you want to call a function there. So instead of someLib... just call the function directly like process.send(data). Or you can do something what is just below where you've pointed me. – Frobisher

Sry you misunderstood me, someLib.on is called once, my code was just a short version. I edited my question. – Emaemaciate

Ok, now it makes sense. I guess the problem is in the someLib somewhere. – Frobisher

Must be, would like to find out. – Emaemaciate