StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
text
Body
copied!<p>OK, here's the problem: the Async attribute is for the case where your page is going to call some long-running task that also blocks the thread, and then your page needs the output from that task in order to return info to the user. For example, if your page needed to call a web service, wait for its response, and then use the data from the response to render your page. </p> <p>The reason you'd use the Async attribute is to avoid blocking the thread. This is important because ASP.NET applications use a thread pool to serve requests, and there are only a relatively small number of threads available. And if each call ties up the thread while waiting on the web service call, then soon you're going to hit enough concurrent users that users are going to have to wait until these web service calls complete. The Async attribute lets the thread return to the thread pool and serve other concurrent visitors to your web site, rather than forcing it to sit still doing nothing while waiting for the web service call to return.</p> <p>The upshot for you is this: the Async attribute is designed for the case where you can't render the page until the asynchronous task completes, and that's why it doesn't render the page immediately.</p> <p>You need to launch your own thread, and make it a daemon thread. I don't remember the exact syntax for that, but you can easily find it in the doc by searching the BCL doc for "daemon". This means the thread will keep your application from shutting down while it is alive, which is important because ASP.NET and IIS reserve the right to "recycle your process" when they deem it necessary, and if that happens while your thread is working, your task will be stopped. Making the thread daemon will prevent this (except for some possible rare edge cases ... you'll find out more when you find the documentation on this).</p> <p>That daemon thread is where you will kick off these tasks. And after you've told the daemon thread to do the task, you can immediately render your page ... so the rendering of the page will happen immediately.</p> <p>Even better than a daemon thread in your ASP.NET process, though, would be to implement a Windows Service for doing the task. Have your ASP.NET application communicate the task to be performed to the Service. No need for a daemon thread and no need to worry about your ASP.NET process being recycled. How do you tell the Service to do the task? Perhaps through WCF, or perhaps by inserting a record into a database table that the Service polls. Or a number of other ways. </p> <p>EDIT: Here's another idea, which I have used before for this very same purpose. Write the info about your task into an MSMQ queue. Have another process (maybe even on another machine) pull from that queue and do the time-consuming task. The job of inserting into a Queue is optimized to return as quickly as possible, so your thread won't block while the data you put in the Queue is sent across the wire or anything like that. It is one of the fastest ways to make note of the fact that a task needs to be done without waiting for that task to execute.</p>

Querying!

Guidance

An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload