ASP.NET MVC and Ajax, concurrent requests?

Question

AJAX newbie here!
At the moment in my ASP.NET MVC web app my AJAX requests appear to be getting batched or queued, im not sure.
No requests seem to be getting completed until the previous request has finished.
How do I go about getting the requests to return independantly?
I dont necessarily want someone to give me the answer but maybe some links to good tutorials or resources which could help. Thanks

Answer 1

Http requests are asynchronous, so there is nothing specifically you need to do to enable this.

However, depending on what is happening behind the ajax call, could affect the order of response. For example - if they were making calls to a service which could only deal with 1 request at a time it would be entirely reasonable for one ajax request to not return until its predecessor had done so.

Perhaps some more information on what the ajax call is actually doing.

Answer 2

I suggest using jQuery for your ajax needs with asp.net mvc, I have used it exclusively and it has been extremely easy.

As for tutorials I would look at this: http://docs.jquery.com/Ajax

There are tons of options to play with and I also suggest downloading firebug so you can watch requests launch from your page asynchronously and see if they fire and what they return etc.

Like the other guy side, AJAX request are asynchronous and don't get queued up and they all return independently when they finish, so if you watch in firebug it will be easy to see what is going on behind the scenes and before the debugger gets hit

Answer 3

ASP.NET will serially process requests on a per-session basis unless sessions are configured as disabled or read only in web.config via the enableSessionState attribute on the pages element.

As this is a page setting, this will not affect MVC controllers and they will still be subject to serial request processing.

Curiously, even with sessions disabled or set to readonly, we can still read and write session data. It seems to only affect the session locking that causes serial request processing.

<system.web>
    <pages enableSessionState="ReadOnly"/>
</system.web>

Pages can also have an enableSessionState property, though this is not relevant to MVC views.

<%@ Page EnableSessionState="True" %>

Answer 4

I'm expanding on Lachlan Roche's answer, which is correct.

The ASP.NET framework will "single-thread" requests that deal with Session scope (a global resource), to prevent one request from interfering with another. In WebForms I think you can use the Page directive to specify that individual pages don't use Session and therefore don't need to treated synchronously like this.

The problem is that in ASP.NET MVC all requests use Session, because it's used to implement TempData. You can disable session state entirely, as Lachlan Roche pointed out, or you can deal with this on a case-by-case basis.

A possible solution might be to kick off your own background threads to process any long-running code, so that the initial request "completes" as quickly as possible.