DOCUMENT:Q75009  06-NOV-1999  [win16ddk]
TITLE   :Using Call_Priority_VM_Event
PRODUCT :Microsoft Windows Device Driver Kit
PROD/VER::3.0
OPER/SYS:
KEYWORDS:

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - Microsoft Windows Device Development Kit (DDK) for Windows, version 3.0 
-------------------------------------------------------------------------------

SUMMARY
=======

Call_Priority_VM_Event is one of the most valuable virtual device (VxD) calls
available. When an application is at a point where the state of the system keeps
the VxD from completing, a call to Call_Priority_VM_Event causes the process to
yield until the system is in such a state that the VxD can continue.

Under most circumstances, using this function will cause events to be processed
in a specific manner. Note, however, that any number of events can occur between
the call to Call_Priority_VM_Event and the call to the event handler specified
as a parameter in the Call_Priority_VM_Event call.

If a VxD intermittently has problems, they may be caused by the code assuming
that the handler is called before certain other actions occur. Also note that a
VxD may be re-entered before the handler is called, causing another call to
Call_Priority_VM_Event before the first handler is called.

If two or more handlers are set up at once, they will usually be called in
last-in, first-out (LIFO) order; however, this is not guaranteed. If
Call_Priority_VM_Event is used, VxD code must be written to be completely
re-entrant and it must allow the handlers to be called in any order.

Additional query words: 3.00 VxD Call_Priority_VM_Event reentrant

======================================================================
Keywords          :  
Technology        : kbAudDeveloper kbWin3xSearch kbWinDDKSearch kbWinDDK300
Version           : :3.0

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1999.