This entry point is used for six WinHLLAPI functions that often take a long time to complete. With WinHLLAPIAsync, the function will be launched asynchronously and will not interfere with the continued progression of the calling application. These functions are: Wait (04), Start Host Notify (23), Start Close Intercept (41), Start Keystroke Intercept (50), Send File (90), and Receive File (91), and are described in WinHLLAPI Extension Functions.

HANDLE WinHLLAPIAsync (HWIND hWnd, LPWORD lpnFunction, LPBYTE lpData, LPWORD lpnLength, LPWORD lpnRetC)*

The parameter list is the same as WinHLLAPI except a window handle is required before the function number. Since the function operates asynchronously, its completion is signaled by a registered message. The window handle is required as the target of the message.

There are two messages that must be registered by the WinHLLAPI application through calls to RegisterWindowsMessage() with the strings WinHLLAPIAsync(for all functions except 90 and 91) and WinHLLAPIAsyncFileTransfer (for functions 90 and 91). The standard format is as follows:
contains the Task Handle returned by the original function call.
the high word contains the error code and the low word contains the original function number.