why settimeout blocks eventloop

Question

Note: this is not a replicated post for those about settimeout, the key answer here is browser design options.

I am starting study node.js: A simple example to test async:

var http=require('http');

http.createServer(
    function(request, response){


        response.writeHead(200);
        response.write("Hello, dog is running");
        setTimeout(
            function(){
                response.write("Dog is done");
                response.end();
            },
            10000
        );

    }
).listen(8080);
console.log("Listen on port 8080")

One interesting thing is its behavior is differernt when in command lind with curl and in browser: In Ubuntu 12.10, I use curl localhost:8080 in two consoles, they response in almost same 10 sends.

However, I open two browsers, make the request at almost same time, but the whole procedure took me 20 seconds?

thanks.

possible duplicate of Nodejs one request blocks another requests — Matt Ball
– Matt Ball, Commented Apr 6, 2013 at 14:21
@MattBall, I don't think it's a duplicate. This one doesn't do CPU intensive processing. Also, it works correctly using CLI (curl) for me, but not in Firefox. — Dogbert
– Dogbert, Commented Apr 6, 2013 at 14:25
Looks like browser isn't sending the second request until the first one ends. If you add a log statement to the start of the handler, it'll demonstrate this. — Dogbert
– Dogbert, Commented Apr 6, 2013 at 14:29
I edit the post because of new finding, it is differernt when use console with command curl and in browsers. Guys, please help me. — Kuan
– Kuan, Commented Apr 6, 2013 at 15:29

generalhenry · Accepted Answer · 2013-04-06 17:30:21Z

19

It's the browser waiting, not node.js

If you run the server and request http://localhost:8080/ in two tabs it takes 20 seconds because the browser waits for the first request to the same url before starting the second.

If you run the server and request http://localhost:8080/1 and http://localhost:8080/2 in two tabs it takes 10 seconds again.

answered Apr 6, 2013 at 17:30

generalhenry

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2 Comments

Kuan Over a year ago

Can you tell me more about how the browser works? Why they can not open the same url with tabs at the same time?

Mustafa Over a year ago

Chrome does not issue any requests simultaneously to the same URL, it is an implementation choice.

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