Q74197: Minimizing Lock and Unlock Calls in Protected Mode

Article: Q74197
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.0,3.1
Operating System(s): 
Keyword(s): kb16bitonly
Last Modified: 05-NOV-1999

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) versions 3.0, 3.1 
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SUMMARY
=======

When Microsoft Windows is running in protected mode (standard mode or enhanced
mode), the selector of a movable memory block does not change even though
Windows may move the block in physical (standard mode, enhanced mode) or linear
(enhanced mode) memory.

Applications that run only in protected mode can take advantage of this behavior
to minimize the number of GlobalLock() and GlobalUnlock() calls.

MORE INFORMATION
================

The following code demonstrates how to allocate a global memory object:

     HANDLE hMem;
     LPSTR lpstr;

     if ((hMem = GlobalAlloc(GMEM_MOVEABLE, cb)) != NULL)
        if ((lpstr = GlobalLock(hMem)) != (LPSTR)NULL)
           {
           // use the memory
           }

The following code demonstrates how to free the global memory object allocated
above:

     if (GlobalUnlock(hMem) != (HANDLE)NULL)
        GlobalFree(hMem);

Leaving movable global memory objects locked does not impose a memory consumption
penalty in protected mode.

This technique is not appropriate for an application that runs in real mode under
versions of Windows prior to version 3.1. In real mode, Windows manages a
limited amount of memory (less than 640K) by moving and discarding memory
blocks. When an application locks a memory block, Windows cannot move or discard
the block. Therefore, an application that runs in real mode must lock an object
only while the object is in use.

Additional query words: 3.00 3.10

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Keywords          : kb16bitonly 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK300 kbWinSDK310
Version           : WINDOWS:3.0,3.1

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