Node.js - Scaling Application

Node.js - Scaling Application

Node.js is running in a single-thread mode but it uses an event-driven paradigm to manage competition. It also facilitates the creation of child processes on multi-core CPU based systems to leverage parallel processing.

Infant processes always have three streams child.stdin, child.stdout, and child.stderr that can be shared with parent process stdio streams.

Node provides module child process with the following three main ways to create a child process.

The exec() method

The method child_process.exec executes a command in a shell and buffers the output. It has a signature of –

child_process.exec(command[, options], callback)

Parameter

The definition of the parameters is used here-

The exec() method returns a fixed size buffer and waits for the cycle to finish and tries to restore all of the buffered data at once.

Example

Creating two javascript files called support.js and master.js –

console.log("Child Process " + process.argv[2] + " executed." );

const files = require(‘files’);
const child_process = require('child_process');
for(var i=0; i<3; i++) {
var workerProcess = child_process.exec('node support.js '+i,function 
(error, stdout, stderr) {
if (error) {
console.log(error.stack);
console.log('Error code: '+error.code);
console.log('Signal received: '+error.signal);
}
console.log('stdout: ' + stdout);
console.log('stderr: ' + stderr);
});
workerProcess.on('exit', function (code) {
console.log(''Exit child process with exit code '+code);
});
}

$ node master.js

Child process exited with exit code 0
stdout: Child Process 1 executed.
stderr:
Child process exited with exit code 0
stdout: Child Process 0 executed.
stderr:
Child process exited with exit code 0
stdout: Child Process 2 executed.

The spawn() Method

child_process.spawn(command[, args][, options])

Parameter

The definition of the parameters is used here-

The spawn() method returns streams (stdout & stderr), which should be used when a volume of data is returned by the process. Spawn() starts receiving the answer as soon as the executing phase begins.

Example

Creating support.js and master.js two javascript files-

console.log("Child Process " + process.argv[2] + " executed." );

const files = require('files');
const child_process = require('child_process');
for(var i = 0; i<3; i++) {
var workerProcess = child_process.spawn('node', ['support.js', i]);
workerProcess.stdout.on('data', function (data) {
console.log('stdout: ' + data);
});
workerProcess.stderr.on('data', function (data) {
console.log('stderr: ' + data);
});
workerProcess.on('close', function (code) {
console.log('child process exited with code ' + code);
});
}

$ node master.js

stdout: Child Process 0 executed.
child process exited with code 0
stdout: Child Process 1 executed.
stdout: Child Process 2 executed.
child process exited with code 0
child process exited with code 0

The fork() Method

Method child process.fork is a special case of spawn() generating Node Processes. It has a signature of –

child_process.fork(modulePath[, args][, options])

Parameters

The definition of the parameters is used here-

In addition to having all the methods in a normal ChildProcess case, the fork method returns an object with an integral communication channel.

Example

Creating support.js and master.js two javascript files-

console.log("Child Process " + process.argv[2] + " executed." );

const fs = require('fs');
const child_process = require('child_process');
for(var i=0; i<3; i++) {
var worker_process = child_process.fork("support.js", [i]);	
worker_process.on('close', function (code) {
console.log('child process exited with code ' + code);
});
}

$ node master.js

Child Process 0 executed.
Child Process 1 executed.
Child Process 2 executed.
child process exited with code 0
child process exited with code 0
child process exited with code 0