If a socket is in the blocking mode, the socket will not relinquish control until a socket command has been completed.

All windows applications will stop, no communications can occur between applications, and the active window cannot be changed.

For this reason, asynchronous notification is included in order to prevent thread blocking. This is mostly useful in Windows 3.X. Nevertheless, a lot of programmers will be making even Windows NT programs with single threads, and so asynchronous read/write capabilities are still useful. In fact, even if you do use separate threads for sockets calls, you'll find that as soon as you make a blocking call on one thread, you'll have to wait until it's done to use it, or you have to create another thread. Windows non-blocking extensions are useful for all of Windows programming.

The Windows Socket classes provide support for internal notification and external notification. This provides a way for you to make calls and to be notified upon completion of the call. You don't have to respond to the Winsock asynchronous notification system yourself if you don't want to, or you can take care of all notifications yourself.

You may want to use notifications for the following classes: