Monday, June 08, 2009

Multithreading: APM and options for waiting until work completes

by luisabreu via LA.NET [EN] on 6/8/2009 8:50:47 AM

In the last post, we’ve started looking at oldest asynchronous pattern of the .NET framework: the APM model. Today, we’re going to list the available options for waiting to the completion of an asynchronous operation started through a framework that implements APM pattern.

After kicking off an asynchronous operation, we have four available options:

• we can block the thread until work is completed by calling the EndXXX method directly. This is a good approach when we have a couple of extra things to do and, after that, we really need to wait until the asynchronous operation completes;
• we can wait on the IAsyncResult’s WaitHandle (AsyncWaitHandle property) until the work that is being executed in parallel ends;
• we can poll the IAsyncResult’s IsCompleted property. This is also a good option when we want to perform other tasks while the asynchronous operation is running;
• we can pass a callback (WaitCallback parameter passed to the BeginXXX method) that is to be called when the operation completes. This is a good option when we don’t need to block the “main” thread until the operation completes and relies on a “continuation passing” style, where a closure is executed when the async operation ends.

As you can see, the APM model gives us several options  and we’ll take a detailed look at each in the next posts. Keep tuned for more.