How can I restart a Node.js child process

Question

I'm trying to restart a certain child_process by the name of serverSpawnProcess. I can get it to stop, but I can't start it again.

serverSpawnProcess.stdin.write('stop\n');
serverSpawnProcess = null;
setTimeout(function() {
  serverSpawnProcess = spawn('java', [
    '-Xmx512M',
    '-Xms512M',
    '-jar',
    'server_files/minecraft_server.jar',
    'nogui'
  ]);
  response.send('r');
}, 10000);

is how I thought I'd go about it, but it only stops the server, it won't spawn it again. Node.js 5.3.0 if that helps.

EDIT For the sake of anyone else looking for how to do this, I ended up putting the spawn into a function, which I call like so

serverSpawnProcess.on("close", function() {
    response.send('r2');
    // Wait for process to exit, then run again

    startServer();
 });

Have you taken a look at the [error](https://nodejs.org/api/child_process.html#child_process_event_error) event from the newly spawned process? What does that say? — Ross, Dec 21 '15 at 17:45

camwhite · Answer 1 · 2019-02-14T01:55:30.467

The way in which I have accomplished this is as follows. Say I have a camCmd which allows me to run a DSLR camera as my webcam, but it crashes periodically. The goal is to restart it automatically without disrupting the stream. The code below does exactly that.

const { spawn } = require('child_process')

const camCmd = `gphoto2 --stdout --capture-movie | \
  ffmpeg -i - -vcodec rawvideo -pix_fmt yuv420p \
  -loglevel error -f v4l2 /dev/video1`

const respawn = spawned => {
  spawned.on('close', () => {
    respawn(spawn(camCmd, { shell: true }))
  })
}
respawn(spawn(camCmd, { shell: true }))

Very simply it's a recursive function with an argument of whatever you're spawning. Which, once closed calls itself with the newly spawned arg.

score 1 · Accepted Answer · edited May 23 '17 at 12:07

So my guess is after 10 seconds timeout your minecraft server is still running (according to docs it saves some data to disk and stuff) and when you try to run another instance it fails due to port still being used.

Try it like this:

serverSpawnProcess.stdin.write('stop\n');
serverSpawnProcess.on("close", function() {
    // Wait for process to exit, then run again

    serverSpawnProcess = spawn('java', [
        '-Xmx512M',
        '-Xms512M',
        '-jar',
        'server_files/minecraft_server.jar',
        'nogui'
    ]);
});

Also as https://stackoverflow.com/users/1139700/ross suggests, add a listener to error event so you know exactly what your problem is.

serverSpawnProcess.on("error", function(err) {
    // ugh, something went wrong
    console.log("Server error:", err);
});

score 0 · Answer 3 · answered Dec 21 '15 at 18:45

Under what conditions are you trying to restart it? When it errors out, or on a specific condition? If the former, check out: http://schier.co/blog/2013/01/06/restarting-workers-in-a-nodejs-cluster.html

I was able to set up my server to auto-restart on errors by nesting my server in the following method, modified from the link above:

var cluster = require('cluster');

if (cluster.isMaster) {
    cluster.fork();

    cluster.on('exit', function(deadWorker, code, signal) {
        // Restart the worker
        var worker = cluster.fork();

        // Note the process IDs
        var newPID = worker.process.pid;
        var oldPID = deadWorker.process.pid;

        // Log the event
        console.log('worker '+oldPID+' died.');
        console.log('worker '+newPID+' born.');
    });
} else {
  // server code is initialized here
}

I'm trying to restart it when I call an express `get` request to `/restartserver`, but I'll keep this answer in mind for later implementation. — gmemstr, Dec 21 '15 at 18:47

score 0 · Answer 4 · answered Dec 22 '15 at 04:04

  var serverSpawnProcess = spawn('java', [
    '-Xmx512M',
    '-Xms512M',
    '-jar',
    'server_files/minecraft_server.jar',
    'nogui'
  ]);

serverSpawnProcess.on('exit', function (code)
{
    console.log("exit here with code: ", code);
});
serverSpawnProcess.stdout.on('data', function (data) {
    console.log('stdout: ' + data);
});

serverSpawnProcess.stderr.on('data', function (data) {
    console.log('stderr: ' + data);
});

How can I restart a Node.js child process

4 Answers4