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Q21581: Shrinking Heap Space

Article: Q21581
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.0,3.1
Operating System(s): 
Keyword(s): kb16bitonly
Last Modified: 06-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 an application calls LocalAlloc() and there is not enough memory within the
application's data segment, Windows will use memory from the global heap to
append this to the application's data segment. Releasing the memory that was
temporarily requested then becomes an issue to the programmer.

For example, an initial HEAPWALK shows 12000 bytes free. After a 4K LocalAlloc()
and LocalLock(), HEAPWALK shows 4000 bytes locked and 8000 free. Then the
program allocates and locks another 10K piece; HEAPWALK shows 4000 bytes locked,
8000 free, and 10000 locked. If the program then deallocates the 4K and 10K
blocks with unlock and free, HEAPWALK shows a free 12000 bytes and a free 10000
bytes. The programmer then has the problem of releasing the second free 10K
block.

Using the LocalShrink() function will compact and shrink the data segment to the
smallest size possible. LocalShrink() cannot move FIXED or locked blocks when
compacting the local heap. Therefore, there may still be free space in the heap,
and the size of the heap may not be as small as requested after calling
LocalShrink(). However, this function will compact as much as possible, given
this constraint.

Additional query words: 3.00 no32bit 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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