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Using this support function, you can set a special callback function that will be used for handling asynchronous I/O operations.

BOOL ServerSupportFunction(
      HCONN ConnID,
      DWORD dwServerSupportFunction,
      PFN_HSE_IO_COMPLETION pfnIOCompletion,
      LPDWORD lpdwSizeofBuffer,
      LPDWORD lpdwContext


  • ConnID
    Specifies the connection identifier of the client to which the response data should be sent.

  • dwServerSupportFunction
    The name of the Server Support function, which in this case must be set to HSE_REQ_IO_COMPLETION.

  • pfnIOCompletion
    Points to the function, of type PFN_HSE_IO_COMPLETION Function, which will be called when the pending I/O operation has completed.

  • lpdwSizeofBuffer
    Unused in this ServerSupportFunction request type.

  • lpdwContext
    Points to an application-defined context structure. This pointer will be passed as a parameter when the callback function is invoked, after the pending I/O operation has completed.


Note that this support function does not actually perform any asynchronous I/O operations itself.

If the callback function is set to NULL, the callback function will never be called by IIS. If this support function is called multiple times, only the callback function specified by the last function call will be honored by IIS. All previous callback function settings will be lost.

If there is an error performing an asynchronous I/O operation, IIS will make exactly one call to the callback function that is specified by pfnIOCompletion in this support function. It is then your ISAPI extension's responsibility to do the necessary cleanup of any allocated resources associated with that operation.


Client: Requires Windows XP Professional, Windows 2000 Professional, or Windows NT Workstation 4.0.

Server: Requires Windows Server 2003, Windows 2000 Server, or Windows NT Server 4.0.

Product: IIS

Header: Declared in httpext.h.

See Also