Running async processes in node.js on multiple cores

Question

Using the async and child_process modules, I can create true "parallel" processing. My question is, how can I ensure that it is running on multiple cores?

var cp = require('child_process');
var async = require('async');
async.parallel([
 function(callback){
 console.log('1');
 var k = cp.fork('./doOther.js',['01']); //how can I ensure the child process k runs on a different core than this process?
 k.on('message',function(msg){
 console.log(msg);
 callback();
 });
 },
 function(callback){
 console.log('2');
 var k = cp.fork('./doOther.js',['02']); //how can I ensure the child process k runs on a different core than this process?
 k.on('message',function(msg){
 console.log(msg);
 callback();
 });
 },
 function(callback){
 console.log('3');
 var k = cp.fork('./doOther.js',['03']); //how can I ensure the child process k runs on a different core than this process?
 k.on('message',function(msg){
 console.log(msg);
 callback();
 });
 },
 function(callback){
 console.log('4');
 var k = cp.fork('./doOther.js',['04']); //how can I ensure the child process k runs on a different core than this process?
 k.on('message',function(msg){
 console.log(msg);
 callback();
 });
 }
],function(){
 console.log('done.');
 process.exit(0);
});

The above script interacts with IPC (inter-process comm) with this script:

//doOther.js, a simple script that interacts with the script above
 process.on('message', function(m) {
 console.log('CHILD got message:', m);
 });
 setTimeout(function(){
 process.send({ foo: process.argv[2] });
 },1000);

Answer 1

Notice a pattern in the array of your async.parallel call? All the functions are the same except for a single number.

And, judging by the repeated comment for each function, you just copied the first version of the function and changed that one number.

You should create a loop that pushes functions into the array, changing that single number each time.

for(var i = 0; i < 4; i++) {
 array.push(function(callback) {
 console.log(i + 1);
 var k = cp.fork('./doOther.js',['0' + (i + 1)]);
 k.on('message',function(msg){
 console.log(msg);
 callback();
 });
 }
}

As another tip, if you aren't going to use k again, don't store cp.form(...,...); in a variable; just continue the .on stuff that you were doing to the k but to the cp.form(...,...).

That would look like this:

cp.fork('./doOther.js', ['0' + (i + 1)]).on('message', function(msg) {
 console.log(msg)
 callback();
});

---

Other than that, I'm not too familiar with node.js and what a core is, so I can't help you on that part.

• Alexander Mills: cores just means CPU
• Suresh Mahawar: can we increase loop count upto 5000 or more to fork cp?