I am working in node, as it happens via a visual studio code extension. I successfully create child processes and can terminate them on command. I am looking to run code when the process unexpectedly exits, this appears to be what the "exit" event is intended for, but I'm unclear on how to call it, this is the code I am working with, the process runs, but does not detect/log on exit, note that output.append is visual studio code specific version of console.log():
child = exec('mycommand', {cwd: path},
function (error, stdout, stderr) {
output.append('stdout: ' + stdout);
output.append('stderr: ' + stderr);
if (error !== null) {
output.append('exec error: ' + error);
}
});
child.stdout.on('data', function(data) {
output.append(data.toString());
});
Here's four things I have tried that do not work in logging on exit:
child.process.on('exit', function(code) {
output.append("Detected Crash");
});
child.on('exit', function(code) {
output.append("Detected Crash");
});
child.stdout.on('exit', function () {
output.append("Detected Crash");
});
child.stderr.on('exit', function () {
output.append("Detected Crash");
});
Looking at the node.js source code for the child process module, the .exec() method does this itself:
child.addListener('close', exithandler);
child.addListener('error', errorhandler);
And, I think .on() is a shortcut for .addListener(), so you could also do:
child.on('close', exithandler);
child.on('error', errorhandler);
Related
I am new to node.js and following some tutorials. In one of them, I execute the following code and expect to shutdown the terminal gracefully which is not the case
process.stdin.resume();
process.stdin.setEncoding('utf8');
process.stdin.on('data', function(chunk) {
process.stdout.write('Data! -> ' + chunk);
});
process.stdin.on('end', function() {
process.stderr.write('End!\n');
});
process.on('SIGTERM', function() {
process.stderr.write("Why are you trying to terminate me?!? :-)");
});
console.log("Node is running as process #" + process.pid);
It works fine, but when I issue, from another terminal the following
taskkill /PID 29884 /F
I don't get the function
process.on('SIGTERM', function()....
get executed.
I came across a thread here at
What is the Windows equivalent of process.on('SIGINT') in node.js?
I get the same behavior, killing the process just goes back to the command line
Then I tried to update the code I got from the thread with some code in order to reprint the Data I enter on the console, it is not getting there (I added rl.on("data", function(chunk))
(process.platform === "win32") {
var rl = require("readline").createInterface({
input: process.stdin,
output: process.stdout
});
rl.output.setEncoding('utf8');
console.log("Node is running as process #" + process.pid);
rl.on("data", function(chunk) {
this.output.write('Data! -> ' + chunk);
});
rl.on("SIGINT", function() {
process.emit("SIGINT");
});
};
process.on("SIGINT", function() {
//graceful shutdown
process.exit();
});
The
rl.on("data", function(chunk) {
this.output.write('Data! -> ' + chunk);
});
just sends back 'Data! -> ' string without the text I enter in the console as the case with the 1st code from the tutorial. What is missing?
Of course, In both cases
process.stderr.write("Why are you trying to terminate me?!? :-)");
is not getting executed
Thanks
I'm working on a Node.js app utilizing Electron. I need to access a executable in a certain directory and determine its output. The executable is a simple console application. I read the docs on Child Process and tried to use execFile. However, the callback function doesn't seem to execute.
Here's my code at the moment:
var exec = require('child_process').execFile
exec('E:/SteamLibrary/steamapps/common/GarrysMod/bin/gmad.exe', [], function(err, data) {
console.log(err);
console.log(data);
});
How could I go about fixing this?
Youre using windows so execFile() wouldnt work. It stated on docs.. for convenient I use docs example here with litle change.
const { spawn } = require('child_process');
const bat = spawn('C/steam/steam.exe');
bat.stdout.on('data', (data) => {
console.log(data.toString());
});
bat.stderr.on('data', (data) => {
console.log(data.toString());
});
bat.on('exit', (code) => {
console.log(`Child exited with code ${code}`);
});
I have a NodeJs application running in the following directory
First Application's Path '/users/user1/projects/sampleProject' which is running at 3000 port.
Second Application's Path '/users/user1/demoProjects/demo1' which is going to run at 5000 port on triggering the router function from first application.
The second NodeJs application is not yet started(It will run at port 5000). It need to run independently on hitting a router function in the first NodeJs Application which is running on port 3000 ie(http://localhost:3000/server/startServer). I'm new to NodeJs child processes, Kindly correct me if i'm wrong. And suggest me a right way to do it. Thanks
Start another node application using node.js?
I have tried it like below
// First NodeJs application
import { exec } from "child_process";
router.get('/startServer', async (req, res, next) => {
console.log("Initiated request")
let startServerInstance = 'cd "/users/user1/demoProjects/demo1" && npm run dev'; // path for the second NodeJs application
console.log("Server instance path => " + startServerInstance)
try {
// exec from child process, Spawns a shell then executes the command within that shell
let child = exec(startServerInstance, function (err, stdout, stderr) {
if (err) throw err;
else {
console.log("result ")
res.json({
status: 'success'
});
}
});
} catch (error) {
res.json({
status: 'error',
message: error
});
}
});
The above code executes the command and triggered the second application to run in background but it doesn't return anything. Either error or success result.
You need to use stout and stderror to check other server logs. Also your code is not correct. If you use if without {} it will not go to else statement. That is why you don't see 'result' text in console.
import {
exec
} from "child_process";
router.get('/startServer', async (req, res, next) => {
console.log("Initiated request")
let startServerInstance = 'cd "/users/user1/demoProjects/demo1" && npm run dev'; // path for the second NodeJs application
console.log("Server instance path => " + startServerInstance)
try {
// exec from child process, Spawns a shell then executes the command within that shell
let child = exec(startServerInstance, function(err) {
if (err) throw err;
console.log("Server started");
});
child.stdout.on('data', (data) => {
// this is new server output
console.log(data.toString());
});
child.stderr.on('data', (data) => {
// this is new server error output
console.log(data.toString());
});
res.json({
status: 'success'
});
} catch (error) {
res.json({
status: 'error',
message: error
});
}
});
Child process callback is only called once the process terminates. If the process keeps running, callback is not triggered.
Explained here - https://nodejs.org/docs/latest-v10.x/api/child_process.html#child_process_child_process_exec_command_options_callback
I'm looking to build a project based on node that will have a few different websocket connections, I'm fine with the code itself for what I want to do but can't seem to get my head around how to start the websocket modules (code already written and moved to a file named ws.js) to run from the main server.js file.
I have tried spawning as a child process but just get
Error: spawn ws.js ENOENT
I have removed all other code from each file to prevent hidden errors, content of the files are below.
Server.js
var child = require('child_process').spawn('node', ['ws.js']);
child.stdout.on('data', function (data) {
console.log('stdout: ' + data);
});
child.stderr.on('data', function (data) {
console.log('stderr: ' + data);
});
child.on('exit', function (code) {
console.log('child process exited with code ' + code);
});
setTimeout(function() {
child.stdin.write('echo %PATH%');
}, 2000);
ws.js
const Gdax = require('gdax');
const publicClient = new Gdax.PublicClient();
const websocket = new Gdax.WebsocketClient(['BTC-USD', 'ETH-USD']);
websocket.on('message', data => {
/* work with data */
console.log("data received");
});
websocket.on('error', err => {
/* handle error */
});
websocket.on('close', () => {
/* ... */
});
EDIT --------------------------
Thanks for the response below from Elliot server.js now runs without error however the ws.js child never writes to the console so is either not running or failing silently. Any help is appreciated on getting this working.
Cheers
For the console logs, you have to keep in mind that a child process is a new process and does not share a console. You can make it work with spawn(), however, since you are using a child process to execute a nodeJs file, I recommend using child_process.fork() instead of spawn. It is similar to spawn but is specifically used for other nodeJs processes. The benefit is that it makes it much easier for the two processes to communicate.
With that in mind, you can make the following updates:
Server.js:
var child = require('child_process').fork('./ws.js');
child.on('message', function (data) {
console.log('stdout: ' + data);
});
child.on('error', function (data) {
console.log('stderr: ' + data);
});
child.on('exit', function (code) {
console.log('child process exited with code ' + code);
});
ws.js
const Gdax = require('gdax');
const publicClient = new Gdax.PublicClient();
const websocket = new Gdax.WebsocketClient(['BTC-USD', 'ETH-USD']);
websocket.on('message', data => {
/* work with data */
process.send("data received");
});
websocket.on('error', err => {
/* handle error */
});
websocket.on('close', () => {
/* ... */
});
process.send() sends data to its parent process, where a listener (i.e.
child.on('message', callback)) is waiting to receive it.
I'd like to restart my application inside this application using NodeJS and NPM.
It doesn't work with child_process :
var exec = require('child_process').exec;
exec('npm restart', function(error, stdout, stderr) {
console.log('stdout: ' + stdout);
console.log('stderr: ' + stderr);
if (error !== null) {
console.log('exec error: ' + error);
}
});
If your Master process died, there is no way to reanimate him by himself.
Have a look at Nodemon to restart your script.
Another option: you can use forever npm module in order to start and monitor app.
So the restart function like this if from api:
app.get('/restart', function (req, res, next) {
process.exit(1);
});
Or if you are using a cluster approach you can kill the child and fork new one as shown below [checkout cluster documentation for node,
cluster.on('exit', function (worker) {
logger.info('Worker ' + worker.id + ' died :(, starting another one.');
cluster.fork();
});