说明：  Winsock 2服务提供者接口（ Service Provider Interface, SPI）代表着另一端的Wi n s o c k编 程（和Winsock 2API相对应）。Wi n s o c k的一端是A P I，另一端则是S P I。
(Winsock 2 service providers interface (Inter Service Provider face, SPI) represent the other end of the Wi n s o c k program (and corresponding 2API Winsock). Wi n s o c k end of the A P I, the other side is I P S.)