How the Execution Timeout is managed in ASP.NET

As you are probably aware, it is possible to specify the execution timeout of an ASP.NET request through the config file. All you need to do is to set the executionTimeout attribute on the httpRuntime element in either the web.config (for one ASP.NET application) or even the machine.config (to affect all ASP.NET applications):

<httpRuntime executionTimeout="200"/>

According to the online documentation the executionTimeout is a TimeSpan attribute that “specifies the maximum number of seconds that a request is allowed to execute before being automatically shut down by ASP.NET”. (BTW, it doesn’t work in debug mode)

The default value for this attribute has been set to 90 seconds in ASP.NET 1.x and was increased to 110 seconds in ASP.NET 2.0.

Internally the timeout is managed by a timer (an instance of a System.Threading.Timer class) which is fired every 15 seconds.

Internally ASP.NET uses a Timer (an instance of System.Threading.Timer) to invoke the request cancelation process. This timer is fired once every 15 seconds, so if the executionTimeout is set to 3 seconds, in reality the request can timeout at any time between 3 seconds and 18 seconds.

When the timer is fired, a thread from the ThreadPool is used to check all the requests. The ones that have timed out are sent a ThreadAbortException by calling Abort on the thread executing the request.

So as per above, the executionTimeout only specifies the minimum duration that the request is guaranteed to be executed. The actual timeout can happen between executionTimeout and executionTimeout + 15 seconds.

Comments (11)

  1. As you are probably aware Thread.Abort() raises a ThreadAbortException in the thread on which it is invoked,

  2. The class responsible for this is System.Web.RequestTimeoutManager.

  3. Chris Long says:

    This post was incredibly informative and helpful. Thanks for posting it!

  4. James says:

    This info is tough to find.  Thanks for posting!

  5. Minyu says:

    Keep in mind that ThreadAbortException can only be observed by managed code. So if you thread is calling some unmanaged functions, the thread will not be aborted, and therefore the timeout will not be enforced, until the execution returns to the managed world. That can be an arbitrary length of delay depending on what those unmanaged code do.

  6. Thanks says:

    Would nevery have found this anywhere else!

  7. NOTE: The following steps apply to ASP.NET 2.0 (32 bit). They have not been tested in other versions

  8. Jason says:

    Thanks! interesting article though!

  9. Very interesting article with some good (regarding timer and timeout detail) facts.

  10. NOTE: The following steps apply to ASP.NET 4.0 (64 bit). They have not been tested in other versions

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