Nodejs one request blocks another requests

Question

If one request will be take a long time for execution, another tabs will wait until first request will completed. Why? Please explain me. And how to solve it? Here my code:

var http = require("http");
var url = require("url");

http.createServer(function(request, response) {

    if (url.parse(request.url).pathname == '/long')
    {
        function longlong()
        {
            var counter = 0;
            var startTime = new Date().getTime();
            while (new Date().getTime() < startTime + 10000)
            {
                counter++;
            }
            return counter;
        }

        response.writeHead(200, {"Content-Type": "text/plain"});
        response.write(longlong() + '');
        response.end();
    }
    else
    {
      response.writeHead(200, {"Content-Type": "text/plain"});
      response.write(0 + '');
      response.end();
    }

}).listen(8888);

Community · Accepted Answer · 2017-05-23 12:12:20Z

3

Good read:

http://blog.mixu.net/2011/02/01/understanding-the-node-js-event-loop/

A key line from that write up is:

…however, everything runs in parallel except your code

That means expensive I/O should be async but your code can block. but, it's typically expensive I/O that we're worried about blocking on the server.

See this other question for more details with an example: Node.js blocking the event loop?

edited May 23, 2017 at 12:12

CommunityBot

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answered Aug 30, 2012 at 13:09

bryanmac

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1 Comment

swapnilsarwe Over a year ago

…however, everything runs in parallel except your code tells the answer

freakish · Accepted Answer · 2012-08-30 12:56:04Z

1

Because NodeJS is single threaded ( just like browser JavaScript ). It can only process one code at a time. We get the illusion of concurrency, because NodeJS has very fancy queue of code blocks which are fired in an asynchronous way. However once the block is processed no other block can be processed at the same time.

With NodeJS you have to make sure that every request ends (either successfuly or not), otherwise it may crash beyond any help (entire server, not only the request).

Also using process.nextTick instead of classical loop may help your requests work faster ( i.e. be more scalable ).

edited Aug 30, 2012 at 12:56

answered Aug 30, 2012 at 12:50

freakish

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4 Comments

Mikhail Over a year ago

I understood this, but How can I prevent a blocking of another (simple) requests? Can you give me an example, please

freakish Over a year ago

You can't! It will always block every other request. What exactly do you want to achieve? Your request handler doesn't make much sense.

Mikhail Over a year ago

It's just an example. In real world it collects a data from the several async DB requests and process it - regroup, calculate average, preparing to display and it takes ~10 seconds, but another requests waiting this request. I try to understand how to work with it.

freakish Over a year ago

Such CPU intensive tasks shouldn't be done in NodeJS. Try writing a C addon for NodeJS: nodejs.org/api/addons.html or look at process.nextTick.

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