AcceptAsync和BeginAccept的区别

Difference between […]Async and Begin[…] .net asynchronous APIs

Note that most *Async methods (with corresponding *Completed events) are using the Event-Based Asynchronous Pattern.

The older (but still perfectly valid) Begin* and End* is a pattern called the Asynchronous Programming Model.

The Socket class is an exception to this rule;

its *Async methods do not have any corresponding events;

it's essentially just APM done in a way to avoid excessive memory allocations.

The biggest difference between APM and EAP is the thread used for completion notification.

APM will call back on a thread pool thread (unless the request completes synchronously).

EAP will use a cross-framework strategy to call back on a UI thread (if the operation was started from a UI thread).

However, both APM and EAP are being replaced with a much more flexible approach based on the Task Parallel Library.

Since the TPL can wrap APMs easily, older classes will likely not be updated directly; extension methods are used to provide Task equivalents for the old APM methods.

For performance reasons, the BCL/TPL teams decided to review each BCL type and add TAP methods directly instead of using extension methods.

These changes will be in .NET 4.5.