subprocess.kill('SIGINT') is not caught in child process

[croraf]

Main process index.js:

const childProcess = require('child_process');

console.log('started main');

const subprocess = childProcess.exec('node childProcess.js', (error, stdout, stderr) => {
    console.log('error from child process:', error);
    console.log('stdout from child process: .............');
    console.log(stdout);
    console.log(stderr);
    console.log('stdout from child process - end: .............');
});

console.log('last line main');

subprocess.kill('SIGINT');

setTimeout(() => {
    console.log('ended main');
}, 5000);

Child process childProcess.js:

const fs = require('fs');

console.log('child started');

process.on('SIGINT', () => {
    console.log('child ending');
    fs.writeFileSync('test1.txt', 'abc');
    process.exit();
});

fs.writeFileSync('test0.txt', 'abc');

setTimeout(() => {
    console.log('timeout ended');
}, 3000);

When I start node index.js in the terminal I get the following output:

started main
last line main
error from child process: { Error: Command failed: node childProcess.js

    at ChildProcess.exithandler (child_process.js:272:12)
    at ChildProcess.emit (events.js:127:13)
    at maybeClose (internal/child_process.js:933:16)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:220:5)
  killed: true,
  code: null,
  signal: 'SIGINT',
  cmd: 'node childProcess.js' }
stdout from child process: .............
child started
timeout ended


stdout from child process - end: .............
ended main

Meaning that SIGINT handler in child process is not triggered.

(Also text0.txt side-effect file gets created and text1.txt does not. I also tried without setTimeout in child, same thing. I managed to trigger SIGTERM in child by ending the child process in "system monitor" processes list.)

• Version: 9.6.1 and 10.10.0
• Platform: Ubuntu 16.04
• Subsystem: process, subprocess

[mscdex]

It works for me on v10.x. Make sure to use a node branch that is still supported (v9.x is not).

[croraf]

v8.11.4 is LTS, should I use that one, or v10?

[Trott]

v8.11.4 is LTS, should I use that one, or v10?

That's up to you. If in doubt, use LTS. Both are currently supported.

[targos]

I think it happens because subprocess.kill('SIGINT'); is called too early.

[croraf]

@Trott @mscdex I updated to node v10.10.0, and the problem still persists.

[croraf]

@targos But it says in the log above that child process exited with error, and that SIGINT was the cause of exit (error.signal above). It shows SIGTERM as a signal property of error if I use subprocess.kill('SIGTERM').

I also now tried to call subprocess.kill('SIGINT') after 1 second delay, doesn't resolve.

[targos]

I also now tried to call subprocess.kill('SIGINT') after 1 second delay, doesn't resolve.

I tried it and it fixed the error

[croraf]

@targos Completely the same error here. Which OS do you have and node version? And as I said above it throws the error in the childProcess.exec callback that SIGINT terminated the child process abruptly. So it seams that it does register that SIGINT was performed on the process, just the SIGINT handler does not catch it.

[targos]

I have Node 10.10.0 and Linux 4.17.12-200.fc28.x86_64.

With this patch:

--- a/index.js
+++ b/index.js
@@ -12,7 +12,9 @@ const subprocess = childProcess.execFile('node', ['childProcess.js'], (error, st

 console.log('last line main');

-subprocess.kill('SIGINT');
+setTimeout(() => {
+  subprocess.kill('SIGINT');
+}, 1000);

 setTimeout(() => {
     console.log('ended main');

I have this output:

started main
last line main
error from child process: null
stdout from child process: .............
child started
child ending


stdout from child process - end: .............
ended main

[croraf]

OK, you are using .execFile instead of .exec function for executing the child process. I now tried .execFile and that works. This is the difference.

Why is that so?

.execFile on the other hand does indeed send signal too early if delay is not set, as console.log from child and test0.txt side-effect dont happen, so the SIGINT handler is not setup at the time of the interrupt.

But in .exec the handler is setup in time, as the test0.txt side-effect happens.

[targos]

Ah yes, sorry. I switched to execFile to check if the behavior was different but I get the same results with exec.

The difference between execFile and exec as explained by the documentation:

The child_process.execFile() function is similar to child_process.exec() except that it does not spawn a shell by default. Rather, the specified executable file is spawned directly as a new process making it slightly more efficient than child_process.exec().

Since execFile is more efficient than exec, it's possible that the difference in timing makes the test behave differently on your machine.

[croraf]

In case I don't have delay (setTimeout), execFile is executed too fast so the handler doesn't set up in time, but in case of exec the SIGINT handler does set up in time as can be seen from child process' side-effects but for some reason it is not triggered.

In case you have 1-2 seconds timeout execFile works as the concurrency issue is solved, but exec does not. Timing difference shouldn't be an issue here because of introduced delay.

So there is some different bug in the operation of exec function that should be examined.

[croraf]

P.S. I now tried subprocess.kill('SIGINT') on execFile (that works on 10.10.0 node, and Ubuntu 16.04, using a delay as described above) on different environment Windows 7, node 8.9.1 and here process.on('SIGINT' ) handler does not work.

  at ChildProcess.exithandler (child_process.js:275:12)
   at emitTwo (events.js:126:13)
   at ChildProcess.emit (events.js:214:7)
   at maybeClose (internal/child_process.js:925:16)
   at Process.ChildProcess._handle.onexit (internal/child_process.js:209:5)
 killed: true,
 code: null,
 signal: 'SIGINT',
 cmd: 'node ./src/index.js' }

I haven't seen that this has been fixed in higher 8.9.x versions.

[croraf]

#22053

[bnoordhuis]

on different environment Windows 7, node 8.9.1 and here process.on('SIGINT' ) handler does not work

That's mentioned in the process.on(...) documentation:

Windows does not support sending signals, but Node.js offers some emulation [..] Sending SIGINT, SIGTERM, and SIGKILL cause the unconditional termination of the target process.

I'll close this out. It's working as expected and documented.