The Windows Sockets WSACancelAsyncRequest function cancels an incomplete asynchronous operation.

int WSACancelAsyncRequest (

HANDLE hAsyncTaskHandle




[in] Specifies the asynchronous operation to be canceled.


The WSACancelAsyncRequest function is used to cancel an asynchronous operation which was initiated by one of the WSAAsyncGetXByY functions such as WSAAsyncGetHostByName. The operation to be canceled is identified by the hAsyncTaskHandle parameter, which should be set to the asynchronous task handle as returned by the initiating WSAAsyncGetXByY function.

Return Values

The value returned by WSACancelAsyncRequest is zero if the operation was successfully canceled. Otherwise, the value SOCKET_ERROR is returned, and a specific error number may be retrieved by calling WSAGetLastError.


An attempt to cancel an existing asynchronous WSAAsyncGetXByY operation can fail with an error code of WSAEALREADY for two reasons. First, the original operation has already completed and the application has dealt with the resultant message. Second, the original operation has already completed but the resultant message is still waiting in the application window queue.

Note It is unclear whether the application can usefully distinguish between WSAEINVAL and WSAEALREADY, since in both cases the error indicates that there is no asynchronous operation in progress with the indicated handle. [Trivial exception: zero is always an invalid asynchronous task handle.] The Windows Sockets specification does not prescribe how a conformant Windows Sockets provider should distinguish between the two cases. For maximum portability, a Windows Sockets application should treat the two errors as equivalent.

Error Codes

A successful WSAStartup must occur before using this function.
The network subsystem has failed.
Indicates that the specified asynchronous task handle was invalid
A blocking Windows Sockets 1.1 call is in progress, or the service provider is still processing a callback function.
The asynchronous routine being canceled has already completed.

See Also

, WSAAsyncGetHostByName, WSAAsyncGetProtoByName, WSAAsyncGetProtoByNumber, WSAAsyncGetServByName, WSAAsyncGetServByPort

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