websocket javascript read write

Question

I was trying to make a Read\Write function for websocket but i've a problem...

var inarrivo = 0;
var risposta = "";

function RDW_Command(Stringa) {
    var Risposta = "";
    Stringa = "$" + Stringa;
    socket.send(Stringa);
    inarrivo = 0;
    while (inarrivo == 0) {
        doNothing();
    }
    return risposta;
}

function doNothing() {}
socket.onmessage = function (msg) {
    risposta = msg.data;
    inarrivo = 1;
};

The problem is that it freeze when it enter in the while loop.... Any idea to fix it? >.< thank you!! Andrea

Javascript is all about asynchronous function calls. You should read into this. You can't sleeps thread like you are used to from other languages. — Christoph
– Christoph, Commented Jun 21, 2012 at 13:05

Denys Séguret · Accepted Answer · 2012-06-21 13:06:51Z

You program websockets in javascript in the usual (in javascript) event/callback based way.

Here's an example :

var somePackage = {};
somePackage.connect = function()  {
    var ws = new WebSocket('ws://'+document.location.host+'/ws');
    ws.onopen = function() {
        console.log('ws connected');
        somePackage.ws = ws;
    };
    ws.onerror = function() {
        console.log('ws error');
    };
    ws.onclose = function() {
        console.log('ws closed');
    };
    ws.onmessage = function(msgevent) {
        var msg = JSON.parse(msgevent.data);
        console.log('in :', msg);
        // message received, do something
    };
};

somePackage.send = function(msg) {
    if (!this.ws) {
        console.log('no connection');
        return;
    }
    console.log('out:', msg)
    this.ws.send(window.JSON.stringify(msg));
};

You call somePackage.connect to open the connection. After that, the message arrivals are handled in the onmessage handler and to send a message to the server you just call somePackage.send.

Even if this is full of asynchronous calls, that doesn't mean that your program won't immediately react to the arrival of a message (as soon as your other functions have stopped working because you have only one thread).

Esailija · Accepted Answer · 2012-06-21 12:09:39Z

3

This is an infinite loop:

inarrivo = 0;
while (inarrivo == 0) {
    doNothing();
}

The solution is to remove the infinite loop.

answered Jun 21, 2012 at 12:09

Esailija

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4 Comments

Andrea Over a year ago

the function: socket.onmessage = function (msg) { risposta = msg.data; inarrivo = 1; }; Should change inarrivo==1 when a message comes! >:

Esailija Over a year ago

That function will never execute as the browser is busy executing the infinite loop...

Andrea Over a year ago

so it's impossible make a read/write in that way? isnt there a command that exc other thread?

Esailija Over a year ago

You only get one thread in javascript (well you can use WebWorkers but you still have to write async code), so no. Just use callbacks.

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