CODEWITHSUNDEEP
node.jschild-process
user655321
user655321

Reputation: 1732

Two processes created by child_process.exec

I'm writing a pretty simple music server for my Raspberry Pi that will play MP#s on-demand. I can successfully launch an instance of mpg123 using child_process.exec(), but the PID of this new process differs from the process actually decoding the music. This is important to me because I want to track the process in the event of a user wanting to stop the job (child.kill()). I'm executing as follows:

var child = child_process.exec('mpg123 "' + filename + '"');
console.log(JSON.stringify({pid: child.pid});

This outputs {"pid":9444}, and music starts playing. However, when I check ps aux | grep mpg123, I see two different processes:

pi        9444  0.0  0.1   1760   504 pts/1    S+   18:55   0:00 /bin/sh -c mpg123 "/home/pi/test.mp3"
pi        9445 11.0  0.6  14840  3112 pts/1    S+   18:55   0:00 mpg123 /home/pi/test.mp3

This latter process, 9445, is what's actually playing my mp3. If I hang onto child and .kill() upon request, the first job is killed but the second lingers, making the kill ineffective.

Is there a different way to create a process that avoids this, or some better way to kill it? I'd rather not have to track everything (eg, the command I used to create it) and try to track down the 'correct' one based on that (eg, ps aux | grep <filename>).

Upvotes: 0

Views: 1265

Answers (1)

user655321
user655321

Reputation: 1732

According to this page, child_process.execFile(cmd, [args]) will spawn a new subshell, which is the pid of the .exec'd process. The subshell then created my instance of mpg123, which is the process I wanted to kill. Instead, I use:

var child = child_process.execFile('mpg123', [filename]); // note filename isn't enquoted

And when I want to kill it, I can simply:

child.kill(); // works

Upvotes: 1

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