As noted in Blocking/Non blocking & Data Volatility, Windows Sockets implements blocking operations in such a way that Windows message processing can continue, which may result in the application which issued the call receiving a Windows message. In certain situations an application may want to influence or change the way in which this pseudo-blocking process is implemented. The WSASetBlockingHook() provides the ability to substitute a named routine which the Windows Sockets implementation is to use when relinquishing the processor during a "blocking" operation.