Platform SDK: Windows Sockets

WPUQueryBlockingCallback

The WPUQueryBlockingCallback function returns a pointer to a callback function the service provider should invoke periodically while servicing blocking operations.

int WPUQueryBlockingCallback (
  DWORD                     dwCatalogEntryId,                    
  LPBLOCKINGCALLBACK FAR    *lplpfnCallback,   
  LPDWORD                   lpdwContext,                       
  LPINT                     lpErrno                              
);

Parameters

dwCatalogEntryId: [in] Descriptor identifying the calling service provider.
lplpfnCallback: [out] Pointer that receives the blocking callback function.
lpdwContext: [out] Pointer that receives a context value that the service provider must pass into the blocking callback.
lpErrno: [out] Pointer to the error code.

Return Values

If no error occurs, WPUQueryBlockingCallback returns zero and stores a pointer to a blocking callback function in lpfnCallback and an associated context value in lpdwContext. Otherwise, it returns SOCKET_ERROR, and a specific error code is available in lpErrno.

Remarks

The WPUQueryBlockingCallback function returns a pointer to a callback function in lpfnCallback to be invoked periodically during blocking operations. This function also returns a context value in lpdwContext to be passed into the blocking callback.

Under Win32, this function can return NULL in lpfnCallback, indicating that no user defined–blocking hook is installed. In this case, the service provider should use the native Win32 synchronization objects to implement blocking.

LPBLOCKINGCALLBACK is defined as follows:

typedef BOOL ( CALLBACK FAR * LPBLOCKINGCALLBACK )( DWORD dwContext );

The blocking callback will return TRUE if the service provider is to continue waiting for the blocking operation to complete. It will return FALSE if the blocking operation has been canceled with the WSPCancelBlockingCall.

Any missing components of the address will default to a reasonable value if possible. For example, a missing port number will default to zero.

Error Codes

Error code	Meaning
WSAEFAULT	The lpfnCallback or the lpdwContext argument is not a valid part of the process address space.
WSAEINVAL	The dwCatalogEntryId is invalid.

Requirements