node.js non blocking code example failure

Question

Following this link http://greenash.net.au/thoughts/2012/11/nodejs-itself-is-blocking-only-its-io-is-non-blocking/ I'm trying to code two non-blocking functions:

blocking code:

function LongBucle() {
    for (x=0;x<=10000;x++) {
        console.log(x);
    }
}

function ShortBucle() {
    for (x=0;x<=10;x++) {
        console.log("short "+x);
     }
}

LongBucle();
console.log("Long bucle end");

ShortBucle();
console.log("Short bucle end");

Now I try to turn the code into non blocking code so the "console.log("Short bucle end");" should be shown first?

function ShortBucle(callback) {
    for (x=0;x<=10;x++) {
        console.log("corto "+x);
    }
callback(x);
}


function LongBucle(callback) {
    for (x=0;x<=10000;x++) {
        console.log(x);
     }
     callback(x);
}


LongBucle(function(err) {
    console.log('Long bucle end');
});


ShortBucle(function(err) {
   console.log('short bucle end');
});

But it doesn't work. What am I doing wrong?

Calling callback is still blocking, use setImmediate

Fluffy
– Fluffy

2013-11-25 12:08:35 +00:00
Commented Nov 25, 2013 at 12:08 — Fluffy
– Fluffy, Commented Nov 25, 2013 at 12:08

Paul Mougel · Accepted Answer · 2013-11-25 12:10:59Z

1

Adding a callback doesn't make your code asynchronous. As Javascript is a single-threaded language, only one instruction is executed at a given time. This means that this snippet will hang forever, no matter what you do:

function a() {
    while (true) {}
}

a();
console.log('Done.');

To process some amount of code later (ie. asynchronously), you can use process.nexTick() or setImmediate:

function LongBucle(callback) {
    setImmediate(function() {
        for (x=0;x<=10000;x++) {
            console.log(x);
         }
         callback(x);
    })
}

Here is an article explaining process.nextTick() and the event loop in Javascript.

answered Nov 25, 2013 at 12:10

Paul Mougel

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2 Comments

user3032175 Over a year ago

Thank you setImmediate worked but then I should accept this webpage example is wrong? greenash.net.au/thoughts/2012/11/…

Paul Mougel Over a year ago

Which example are you talking about?

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