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Dhanush N
Dhanush N

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Multiprocessing in NodeJs

#node #javascript #webdev #tutorial

A single instance of Node runs in a single thread. To take advantage of multi core systems the user will sometimes want to launch a cluster of Node processes to handle the load. The cluster module allows you to easily create a network of processes that all share server ports.

Code Example

A single threaded NodeJS server would have the following snippet

const http = require('http'); const port = 4000; function init() { startHttpServer(); } function startHttpServer() { var httpsServer = http.createServer(function (req, res) { res.writeHead(200); res.end("Hello Viewer!"); }); httpsServer.listen(port); } init();
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The above code will run on a single core in your multi core environment

So to take advantage of NodeJs process & to fork our process to increase the software throughput, the below changes should be done

const os = require('os'); const http = require('http'); const cluster = require('cluster'); const port = 4000; function init() { if (cluster.isMaster) { let numCPUs = os.cpus().length; console.log(" Num of CPU ", numCPUs); for (let idx = 0; idx < numCPUs; idx++) { cluster.fork(); } } else { startHttpServer(); } } function startHttpServer() { var httpsServer = http.createServer(function (req, res) { res.writeHead(200); res.end("Hello Viewer!"); }); httpsServer.listen(port); } init();
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The cluster & os modules will help us achieve this. The above code gives us information about how much core our environment has.
In my system the Num of CPU is 8 ( This would be different based on your system & environment )
One main thing to notice is that the current process is the master because only the master can fork workers.

Master & Worker Communications

What we have understood untill this is, the cluster module is taking our processes and spawning it again as a separate process in the OS. There is no memory sharing between workers & master. In order to establish this we need to establish a communication message

const os = require('os'); const http = require('http'); const cluster = require('cluster'); const port = 4000; function init() { if (cluster.isMaster) { let numCPUs = os.cpus().length; console.log(" Num of CPU ", numCPUs); for (let idx = 0; idx < numCPUs; idx++) { let worker = cluster.fork(); worker.on('message', function (msg) { console.log("Worker " + msg.worker + " served a " + msg.cmd); worker.send("Good work!"); }); } } else { startHttpServer(); } } function startHttpServer() { process.on('message', function (msg) { console.log(msg); }); var httpsServer = http.createServer(function (req, res) { res.writeHead(200); res.end("Hello Viewer!"); process.send({ worker: cluster.worker.id, cmd: 'request' }); }); httpsServer.listen(port); } init();
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Here we have listeners for both the workers and the master. When the worker receives a request it sends a message to the master, which on receiving is printing some logs on the console and is returning a message to the worker that the worker also prints to the console.

Creating a multi-process NodeJS server is not difficult to do and can vertically scale your software improving its throughput. It is a very important part of using your hardware efficiently and scaling your applications.

Thanks for reading ❤️

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