I have created a small example application in node.js with unit tests and acceptance tests here
Both unit and acceptance tests are run inside mocha process. Acceptance tests start from forking the process and basically running the server on before() method. after() method stops the process and
before((initialized) => {
console.log('before script');
serverProcess = child_process.fork('server.js');
serverProcess.on('close', function (code) {
console.log('child process exited with code ' + code);
});
setTimeout(() => {
console.log('1s elapsed');
initialized();
}, 1000);
The code without any delays works on my local gitlab-runner, however on server it's not always the case, so I have added delay - wait for a while until the server will start.
Empirically I have found that 1s is enough and .5s is not.
However, I would like to know what should I do to make sure that the server is.
Are there any solutions to run server, execute the tests and shutdown the server that works on Linux, Windows, docker and outside of it?
There is a good help about how to communicate between fork processes.
The idea will be to send a message from the child saying to it's dad (I am ready!). Then the dad will continue is work.
Example :
before((initialized) => {
serverProcess = child_process.fork('server.js');
serverProcess.on('close', function(code) {
console.log('child process exited with code ' + code);
});
serverProcess.on('close', function(code) {
console.log('child process exited with code ' + code);
});
// We add a backup plan. If it takes too long to launch, throw
const timeout = setTimeout(() => {
initialized(new Error('tiemout');
}, 30000);
// Cait for the child to send a message to us
serverProcess.on('message', function(str) {
if (str === 'init done') {
clearTimeout(timeout);
// server.js got successfully initialized
initialized();
}
});
});
// To add inside of your server.js listen
if (process.send) {
process.send("init done");
}
Related
Is there a way of ensuring that a child process has been killed?
I currently have the following code:
let p = child_process.spawn(app, args);
...
try{
p.kill('SIGKILL');
} catch(e) {
console.error("Killing process exception:", e);
}
job = setInterval( () => {
if(p.killed || timeout === true){
clearInterval(job);
callback();
}
}, 100);
setTimeout( () => {
console.log("Killing process timeout!");
timeout = true;
}, 1000);
I check periodically (100 ms period) if the killing signal has been properly send to the process and, in that moment, I assume that the process has been killed; but, to ensure that the process is not locked, I set a timeout of 1 second.
Many times the timeout is fired, independently of waiting for 1 second or 10 seconds.
The code below is executed in linux; if working in WSL, then everything seems to work properly
I have a job that is executed ones per day. My app is running on Heroku, and dyno is restarted ones a day.
So what can happen is that during job execution Heroku starts the restart of dyno.
That itself is not a problem as I can start job two times per day, but what is a problem is to stop the job in the middle of task when it is not in stable status.
I would like now somehow to send this signal to job function so I can break any loops and stop function execution in safe way.
I know how to get signal:
process
.on('SIGTERM', shutdown('SIGTERM'))
.on('SIGINT', shutdown('SIGINT'))
.on('uncaughtException', shutdown('uncaughtException'));
function shutdown(signal) {
console.log(`${ signal }...`);
return (err) => {
if (err) console.error(err.stack || err);
setTimeout(() => {
console.log('...waited 5s, exiting.');
process.exit(err ? 1 : 0);
}, 5000).unref();
};
}
but how to send this signal to my job function and to break from it safely?
Thank you.
So the best solution I came up with is following.
// Manage signals
let shutDownSignal = false;
process
.on('SIGTERM', shutdown('SIGTERM'))
.on('SIGINT', shutdown('SIGINT'))
.on('uncaughtException', shutdown('uncaughtException'));
function shutdown(signal) {
return (err) => {
shutDownSignal = true;
console.log(`Received signal: ${ signal }...`);
if (err) console.error(err.stack || err);
setTimeout(() => {
console.log('...waited 15s, exiting.');
process.exit(err ? 1 : 0);
}, 15000).unref();
};
}
module.exports.getShutDownSingnal = function(){ return shutDownSignal; }
then with getShutDownSingnal() anywhere I can check whether shutdown is initiated.
One more thing. It is necessary to put Procfile in app root with
web: node index.js
in it (or app.js depending what are you using).
This is necessary so that SIGTERM and SIGKILL signals are transferred correctly to node (for example if using npm, it will not transfer this signal correctly). More about this on Heroku docs
Maybe this will be useful for someone.
I have an electron app that uses child_process.exec to run long running tasks.
I am struggling to manage when the user exits the app during those tasks.
If they exit my app or hit close the child processes continue to run until they finish however the electron app window has already closed and exited.
Is there a way to notify the user that there are process still running and when they have finished then close the app window?
All I have in my main.js is the standard code:
// Quit when all windows are closed.
app.on('window-all-closed', function() {
// On OS X it is common for applications and their menu bar
// to stay active until the user quits explicitly with Cmd + Q
if (process.platform != 'darwin') {
app.quit();
}
});
Should I be adding a check somewhere?
Thanks for your help
EDITED
I cannot seem to get the PID of the child_process until it has finished. This is my child_process code
var loader = child_process.exec(cmd, function(error, stdout, stderr) {
console.log(loader.pid)
if (error) {
console.log(error.message);
}
console.log('Loaded: ', value);
});
Should I be trying to get it in a different way?
So after everyones great comments I was able to update my code with a number of additions to get it to work, so am posting my updates for everyone else.
1) Change from child_process.exec to child_process.spawn
var loader = child_process.spawn('program', options, { detached: true })
2) Use the Electron ipcRenderer to communicate from my module to the main.js script. This allows me to send the PIDs to main.js
ipcRenderer.send('pid-message', loader.pid);
ipcMain.on('pid-message', function(event, arg) {
console.log('Main:', arg);
pids.push(arg);
});
3) Add those PIDs to array
4) In my main.js I added the following code to kill any PIDs that exist in the array before exiting the app.
// App close handler
app.on('before-quit', function() {
pids.forEach(function(pid) {
// A simple pid lookup
ps.kill( pid, function( err ) {
if (err) {
throw new Error( err );
}
else {
console.log( 'Process %s has been killed!', pid );
}
});
});
});
Thanks for everyones help.
ChildProcess emits an exit event when the process has finished - if you keep track of the current processes in an array, and have them remove themselves after the exit event fires, you should be able to just foreach over the remaining ones running ChildProcess.kill() when you exit your app.
This may not be 100% working code/not the best way of doing things, as I'm not in a position to test it right now, but it should be enough to set you down the right path.
var processes = [];
// Adding a process
var newProcess = child_process.exec("mycommand");
processes.push(newProcess);
newProcess.on("exit", function () {
processes.splice(processes.indexOf(newProcess), 1);
});
// App close handler
app.on('window-all-closed', function() {
if (process.platform != 'darwin') {
processes.forEach(function(proc) {
proc.kill();
});
app.quit();
}
});
EDIT: As shreik mentioned in a comment, you could also just store the PIDs in the array instead of the ChildProcess objects, then use process.kill(pid) to kill them. Might be a little more efficient!
Another solution. If you want to keep using exec()
In order to kill the child process running by exec() take a look to the module ps-tree. They exaplain what is happening.
in UNIX, a process may terminate by using the exit call, and it's
parent process may wait for that event by using the wait system call.
the wait system call returns the process identifier of a terminated
child, so that the parent tell which of the possibly many children has
terminated. If the parent terminates, however, all it's children have
assigned as their new parent the init process. Thus, the children
still have a parent to collect their status and execution statistics.
(from "operating system concepts")
SOLUTION: use ps-tree to get all processes that a child_process may have started, so that they
exec() actually works like this:
function exec (cmd, cb) {
spawn('sh', ['-c', cmd]);
...
}
So check the example and adapt it to your needs
var cp = require('child_process'),
psTree = require('ps-tree');
var child = cp.exec("node -e 'while (true);'", function () { /*...*/ });
psTree(child.pid, function (err, children) {
cp.spawn('kill', ['-9'].concat(children.map(function (p) { return p.PID })));
});
I'm starting to learn and use node and I like it but I'm not really sure how certain features work. Maybe you can help me resolve one such issue:
I want to spawn local scripts and programs from my node server upon rest commands. looking at the fs library I saw the example below of how to spawn a child process and add some pipes/event handlers on it.
var spawn = require('child_process').spawn,
ps = spawn('ps', ['ax']),
grep = spawn('grep', ['ssh']);
ps.stdout.on('data', function (data) {
grep.stdin.write(data);
});
ps.stderr.on('data', function (data) {
console.log('ps stderr: ' + data);
});
ps.on('close', function (code) {
if (code !== 0) {
console.log('ps process exited with code ' + code);
}
grep.stdin.end();
});
grep.stdout.on('data', function (data) {
console.log('' + data);
});
grep.stderr.on('data', function (data) {
console.log('grep stderr: ' + data);
});
grep.on('close', function (code) {
if (code !== 0) {
console.log('grep process exited with code ' + code);
}
});
What's weird to me is that I don't understand how I can be guaranteed that the event handler code will be registered before the program starts to run. It's not like there's a 'resume' function that you run to start up the child. Isn't this a race condition? Granted the condition would be minisculy small and would almost never hit because its such a short snipping of code afterward but still, if it is I'd rather not code it this way out of good habits.
So:
1) if it's not a race condition why?
2) if it is a race condition how could I write it the right way?
Thanks for your time!
Given the slight conflict and ambiguity in the accepted answer's comments, the sample and output below tells me two things:
The child process (referring to the node object returned by spawn) emits no events even though the real underlying process is live / executing.
The pipes for the IPC are setup before the child process is executed.
Both are obvious. The conflict is w.r.t. interpretation of the OP's question:-
Actually 'yes', this is the epitome of a data race condition if one needs to consider the real child process's side effects. But 'no', there's no data race as far as IPC pipe plumbing is concerned. The data is written to a buffer and retrieved as a (bigger) blob as and when (as already well described) the context completes allowing the event loop to continue.
The first data event seen below pushes not 1 but 5 chunks written to stdout by the child process whilst we were blocking.. thus nothing is lost.
sample:
let t = () => (new Date()).toTimeString().split(' ')[0]
let p = new Promise(function (resolve, reject) {
console.log(`[${t()}|info] spawning`);
let cp = spawn('bash', ['-c', 'for x in `seq 1 1 10`; do printf "$x\n"; sleep 1; done']);
let resolved = false;
if (cp === undefined)
reject();
cp.on('error', (err) => {
console.log(`error: ${err}`);
reject(err);
});
cp.stdout.on('data', (data) => {
if (!resolved) {
console.log(`[${t()}|info] spawn succeeded`);
resolved = true;
resolve();
}
process.stdout.write(`[${t()}|data] ${data}`);
});
let ts = parseInt(Date.now() / 1000);
while (parseInt(Date.now() / 1000) - ts < 5) {
// waste some cycles in the current context
ts--; ts++;
}
console.log(`[${t()}|info] synchronous time wasted`);
});
Promise.resolve(p);
output:
[18:54:18|info] spawning
[18:54:23|info] synchronous time wasted
[18:54:23|info] spawn succeeded
[18:54:23|data] 1
2
3
4
5
[18:54:23|data] 6
[18:54:24|data] 7
[18:54:25|data] 8
[18:54:26|data] 9
[18:54:27|data] 10
It is not a race condition. Node.js is single threaded and handles events on a first come first serve basis. New events are put at the end of the event loop. Node will execute your code in a synchronous manner, part of which will involve setting up event emitters. When these event emitters emit events, they will be put to the end of the queue, and will not be handled until Node finishes executing whatever piece of code its currently working on, which happens to be the same code that registers the listener. Therefore, the listener will always be registered before the event is handled.
In my Node.js (v0.10.9) code I'm trying to detect 2 cases:
an external tool (dot) is installed - in that case I want to send some data to stdin of created process
the external tool is not installed - in that case I want to display warning and I don't want to send anything to process' stdin
My problem is that I don't know how to send data to child's stdin if and only if the process was spawned successfully (i.e. stdin is ready for writing).
Following code works fine if dot is installed, but otherwise it tries to send data to the child although the child wasn't spawned.
var childProcess = require('child_process');
var child = childProcess.spawn('dot');
child.on('error', function (err) {
console.error('Failed to start child process: ' + err.message);
});
child.stdin.on('error', function(err) {
console.error('Working with child.stdin failed: ' + err.message);
});
// I want to execute following lines only if child process was spawned correctly
child.stdin.write('data');
child.stdin.end();
I'd need something like this
child.on('successful_spawn', function () {
child.stdin.write('data');
child.stdin.end();
});
From the node.js docs: http://nodejs.org/api/child_process.html#child_process_child_process_spawn_command_args_options
Example of checking for failed exec:
var spawn = require('child_process').spawn,
child = spawn('bad_command');
child.stderr.setEncoding('utf8');
child.stderr.on('data', function (data) {
if (/^execvp\(\)/.test(data)) {
console.log('Failed to start child process.');
}
});
Have a look at core-worker:
https://www.npmjs.com/package/core-worker
This package makes it a lot easier to handle processes.
I think what you want to do is something like that (from the docs):
import { process } from "core-worker";
const simpleChat = process("node chat.js", "Chat ready");
setTimeout(() => simpleChat.kill(), 360000); // wait an hour and close the chat
simpleChat.ready(500)
.then(console.log.bind(console, "You are now able to send messages."))
.then(::simpleChat.death)
.then(console.log.bind(console, "Chat closed"))
.catch(() => /* handle err */);
So if the process is not started correctly, none of the .then statements are executed which is exactly what you want to do, right?