I am learning nodejs, and checked some examples about sending signals to child process, just as following codes, it is said "SIGINT" handler in child should be response, while I did not get any output.

// parent.js
var spawn = require('child_process').spawn;
var child = spawn('node', ['child.js']);

child.stdout.on('data', function(data) {
  console.log('data from child: ' + data);
});

child.kill('SIGINT');


// child.js
console.log('child calling');
process.on('SIGINT', function() {
  console.log('Received SIGINT signal');
});

When I am typing

node parent.js

Why there is no output? even the "child calling" output in the child.js?

Hope anyone help me? Thanks.

In addition, I am not clear when the child.js is executed, at the time the execution of statement? Hope anyone can give a detail explanation? Thanks.

var child = spawn('node', ['child.js']);

I am learning nodejs, and checked some examples about sending signals to child process, just as following codes, it is said "SIGINT" handler in child should be response, while I did not get any output.

// parent.js
var spawn = require('child_process').spawn;
var child = spawn('node', ['child.js']);

child.stdout.on('data', function(data) {
  console.log('data from child: ' + data);
});

child.kill('SIGINT');


// child.js
console.log('child calling');
process.on('SIGINT', function() {
  console.log('Received SIGINT signal');
});

When I am typing

node parent.js

Why there is no output? even the "child calling" output in the child.js?

Hope anyone help me? Thanks.

In addition, I am not clear when the child.js is executed, at the time the execution of statement? Hope anyone can give a detail explanation? Thanks.

var child = spawn('node', ['child.js']);

• javascript
• node.js

1 Answer 1

The first problem is that you spawn a child process and then immediately send it SIGINT. Since the child process (probably) hasn't run at all yet, it hasn't registered for that signal and thus is killed by it. The easiest way to get this working is to just put it in a setTimeout:

setTimeout(function() {
  child.kill('SIGINT');
}, 100);

Now you'll see

data from child: child calling

and then it will exit. But you're expecting the SIGINT message. The problem this time is that the child process logs, registers for the signal, and then is done. node.js will end if it finishes and isn't waiting on anything else. Things it will wait on includes open sockets, setTimeouts, etc. You need it to be doing something, though. As a simple test, you can just add to child.js:

setInterval(function() {
  console.log('hey!');
}, 1000);

Or something like that. Then you'll see the output you're expecting.