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HeapCompact info  Overview  Group

The HeapCompact function attempts to compact a specified heap. It compacts the heap by coalescing adjacent free blocks of memory and decommitting large free blocks of memory.

UINT HeapCompact(

    HANDLE hHeap,

// handle to the heap to compact

    DWORD dwFlags 

// bit-flags that control heap access during function operation



Handle to the heap that the function will attempt to compact.
A set of bit flags that control heap access during function operation. The following bit flag has meaning:




If this flag is set, heap access is not serialized while the HeapCompact function accesses the heap; heap access is not mutually exclusive. It is safe to set this flag only in a limited set of specific situations. For a discussion of those situations and heap serialization in general, see the Remarks section of HeapCreate.

If this flag is clear, heap access is serialized while HeapCompact accesses the heap; heap access is mutually exclusive. This is the safe and simple default condition.

Return Values

If the function succeeds, the return value is the size, in bytes, of the largest committed free block in the heap. This is an unsigned integer value.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

In the unlikely case that there is absolutely no space available in the heap, the function return value is zero, and GetLastError returns the value NO_ERROR.


There is no guarantee that an application can successfully allocate a memory block of the size returned by HeapCompact. Other threads or the commit threshold might prevent such an allocation.

See Also

HeapCreate, HeapValidate

See also:

file: /Techref/os/win/api/win32/func/src/f44_14.htm, 3KB, , updated: 2000/4/7 12:19, local time: 2022/5/18 02:39,

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