This message is available for Ring 3 DLL stream handlers to lock memory objects so they cannot be paged out. Currently, the buffering algorithms and buffer management code of the Sync/Stream Manager locks down stream buffers. Therefore, this message should be used only to lock down code segments or to lock down stack segments so the stream handler does not get swapped out during streaming. You also might use this message in the case of user-provided buffers. For example, if there were a particular type of stream created where the stream handler DLL or source stream handler actually provided application memory buffers, you could use locked memory to lock down buffers that the handler passed to the Sync/Stream Manager. Typically, the Sync/Stream Manager attempts to lock down the buffers anyway.