Architecture :: Main() Execution Loop For Server Or Web App?

I am using multiple threads in my .net web application. Certain functions may need to execute at any arbitrary time. However, I do not need these (and the entire application) to be fully asynchronous, as there is an acceptable tolerance in this execution time. Here is a rough example of what I need to do:

main()
{
loop
{
if (flagA) then doTaskA();
if (flagB) then doTaskB();
}
}

...where flagA and flagB are set via asynchronous timers in critical section. The actual execution of the requested tasks would thereafter run in series.

This is very easy to do in C/C++, etc. But I cannot find any access to such control in .NET, specifically in the web server/application architecture. It may be that it doesn't exist; however, I am assuming that the server must do something of this sort as it manages applications. I would like to hook into that somehow; even if via some application function that is called regularly during this loop.