The Asynchronous Programming Model (APM) is one of the oldest patterns introduced by Microsoft in .NET 1.0 back in 2001 for asynchronous programming handling.

The pattern is easy. To start a deferred job, you simply start such a job by using a Delegate (remote method invoker) and then get an object back of type IAsyncResult to know the status of such a remote operation. Here an asynchronous programmed application to compute file hashes. The application will add a "." to the Starting data computation initial message to acknowledge to the user that the application is still processing. The following examples use the blocking approach:

static void Main(string[] args)
{
    //a container for data
    var complexData = new byte[1024];

    //a delegate object that gives us the ability to trigger the pointed method in async way
    var dataDelegate = new Action<byte[]>(ComputeComplexData);

    Console.Write("Starting data computation...");

    //start...