Spawn and kill a process in node.js
Javascriptnode.jsJavascript Problem Overview
I'm trying to spawn a process in javascript, and kill it after some time (for testing purposes).
In the end, the process will be a infinite loop that I need to restart with different arguments at specified time, so I thought that spawning the process and killing it was the best way to do this.
My test code is:
var spawn=require('child_process').spawn
, child=null;
child=spawn('omxplayer', ['test.mp4'], function(){console.log('end');}, {timeout:6000});
console.log('Timeout');
setTimeout(function(){
console.log('kill');
child.kill();
}, 1200);
child.stdout.on('data', function(data){
console.log('stdout:'+data);
});
child.stderr.on('data', function(data){
console.log('stderr:'+data);
});
child.stdin.on('data', function(data){
console.log('stdin:'+data);
});
The result is:
#~$ node test.js
Timeout
kill
But I still need to send ctrl+C to end the program. What am I missing?
On Raspbian, node 0.10.17, omxplayer is a binary (video player).
I tried:
- Added
chmod +x
to the app. - Launched as root.
- Paused stdin of the child process. Using all terminate-related signal in the kill command.
I also launched a ps
command while the app was running:
2145 bash
2174 node
2175 omxplayer
2176 omxplayer.bin
2177 ps
So omxplayer is a wrapper, who don t kill it's child process when it end, is there any way to get the pid of the wrapped process?
Still biting dust, tried this:
spawn('kill', ['-QUIT', '-$(ps opgid= '+child.pid+')']);
Which I thought would kill all children of omxplayer, I don t know if using spawn like that is wrong or if it's the code that doesn't work.
The last edit I made was the good answer, but had to be edited a bit.
I created a sh file (with execute right) like this:
PID=$1
PGID=$(ps opgid= "$PID")
kill -QUIT -"$PGID"
Which I start like this:
execF('kill.sh', [child.pid], function(){
console.log('killed');
});
Instead of child.kill
.
I'm not sure if it s the best way to do, nor if the code is clean, but it does work.
I'll accept any answer which make it in a cleaner way or, even better, without having to execute a file.
Javascript Solutions
Solution 1 - Javascript
Refer to this discussion
Once you start listening for data on stdin, node will wait for the input on stdin until it is told not to. When either user presses ctrl-d (meaning end of input) or the program calls stdin.pause(), node stops waiting on stdin.
A node program does not exit unless it has nothing to do or wait for. Whats happening is, it is waiting on stdin and therefore never exits.
Try changing your setTimeout callback to
console.log('kill');
child.stdin.pause();
child.kill();
I hope that should work.
Solution 2 - Javascript
There is a really neat npm package called tree-kill
which does this very easily and effectively. It kills the child process, and all child processes that child may have started.
var kill = require('tree-kill');
const spawn = require('child_process').spawn;
var scriptArgs = ['myScript.sh', 'arg1', 'arg2', 'youGetThePoint'];
var child = spawn('sh', scriptArgs);
// some code to identify when you want to kill the process. Could be
// a button on the client-side??
button.on('someEvent', function(){
// where the killing happens
kill(child.pid);
});
Solution 3 - Javascript
I've had exactly the same issue as you with omxplayer and the solution in this blog post worked for me.
var psTree = require('ps-tree');
var kill = function (pid, signal, callback) {
signal = signal || 'SIGKILL';
callback = callback || function () {};
var killTree = true;
if(killTree) {
psTree(pid, function (err, children) {
[pid].concat(
children.map(function (p) {
return p.PID;
})
).forEach(function (tpid) {
try { process.kill(tpid, signal) }
catch (ex) { }
});
callback();
});
} else {
try { process.kill(pid, signal) }
catch (ex) { }
callback();
}
};
// elsewhere in code
kill(child.pid);
Solution 4 - Javascript
Why don't you just send the 'q' value in the stdin pipe ? It kill the omxplayer process.
Solution 5 - Javascript
You've spawned a child process which was successfully killed. However, your main thread is still executing, which is why you have to press Ctrl+C.
Solution 6 - Javascript
Finally, I found how to do it without script:
exec('pkill omxplayer', function(err, stdout, stderr){
if (stdout){console.log('stdout:'+stdout);}
if (stderr){console.log('stderr:'+stderr);}
if (err){throw err;}
//...
}
Solution 7 - Javascript
Try to use child_process.execFile()
method from here.
> The child_process.execFile() function is similar to > child_process.exec() except that it does not spawn a shell. Rather, > the specified executable file is spawned directly as a new process > making it slightly more efficient than child_process.exec().
It works in my case.
Solution 8 - Javascript
You must specify the signal:
child.kill('SIGKILL')
https://nodejs.org/api/child_process.html#child_process_subprocess_kill_signal
Solution 9 - Javascript
In node:16
I was required to destroy()
(pause()
i not enough) the std
channels before sending kill()
. Like this:
cmd.stdout.destroy();
cmd.stderr.destroy();
cmd.kill('SIGINT');