Creating non blocking function - Node.js

Question

Imagine that I have a blocking function like this (the program will wait for the execution of random_operations:

var result = random_operations(arg1,arg2);

But now I make this:

function Op() {
  events.EventEmitter.call(this);

  this.get= function(arg1, arg2)
  {
  this.arg1 = arg1;
  this.arg2 = arg2;
  this.result = random_operations(this.arg1,this.arg2);
  this.emit('done', this.result);
  }
}

Op.prototype.__proto__ = events.EventEmitter.prototype;
var do_job = new Op();

do_job.on('done', function(resulted) {
    console.log('done '+ resulted);
  });

dojob.get(_arg1, _arg2);

Using random_operations like this means that node.js will not block? I am trying to understand how can I non-block the node.js.

Well, it is and it isn't. It will just postpone the execution. If your code takes 5s to run it WILL block the event loop for 5s. No matter what. — klaemo
– klaemo, Commented Dec 11, 2015 at 9:35

Community · Accepted Answer · 2017-05-23 12:04:04Z

2

node.js only does non-blocking I/O (filesystem reads/writes, network requests etc). JavaScript is still single threaded and long-running code will block the event loop.

There are ways to defer such operations or run them in a child process, but that's a little more complicated.

Take a look at this answer

edited May 23, 2017 at 12:04

CommunityBot

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answered Dec 10, 2015 at 23:34

klaemo

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Comments

Brian Cannard · Accepted Answer · 2015-12-10 23:52:54Z

1

You want to use Promise. You could emulate and understand it if pass a function which should be called after the operation completes. With call to setImmediate() you could postpone execution of the code inside that function.

answered Dec 10, 2015 at 23:52

Brian Cannard

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3 Comments

carduh Over a year ago

My objective is to non-block the nodej.js. Promises will block to. @avesus

Brian Cannard Over a year ago

You postpone execution of current part of code with promises and setImmediate(). You could write async code in C++ for node extension. But JavaScript is always run SINGLE-THREADED.

Brian Cannard Over a year ago

The solution I offer is to call lenghty code with setImmediate. It allows it to mix in time with another code.

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