Q75009: Using Call_Priority_VM_Event

Article: Q75009
Product(s): Microsoft Windows Device Driver Kit
Version(s): 3.0
Operating System(s): 
Keyword(s): 
Last Modified: 06-NOV-1999

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The information in this article applies to:

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

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

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