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):
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.