Share via

HeapReAlloc

  • Article

This function reallocates a block of memory from a heap. The allocated memory is not movable.

LPVOID HeapReAlloc(
  HANDLE hHeap, 
  DWORD dwFlags, 
  LPVOID lpMem, 
  DWORD dwBytes 
);

Parameters

  • hHeap
    [in] Heap from which the memory will be reallocated. This is a handle returned by the HeapCreate or GetProcessHeap function.
  • dwFlags
    [in] Specifies several controllable aspects of heap reallocation. Specifying any of these flags overrides the corresponding flag specified in the flOptions parameter when the heap was created using the HeapCreate function. The following table shows flags you can specify. You can specify one or more of these flags.
    Value Description
    HEAP_NO_SERIALIZE Specifies that mutual exclusion is not used while HeapReAlloc is accessing the heap. This flag should not be specified when accessing the process heap. The system may create additional threads within the application's process that simultaneously access the process heap.

    This flag is ignored.
    HEAP_REALLOC_IN_PLACE_ONLY Specifies that there can be no movement when reallocating a memory block to a larger size. If this flag is not specified and the reallocation request is for a larger size, the function may move the block to a new location. If this flag is specified and the block cannot be enlarged without moving, the function fails, leaving the original memory block unchanged.
    HEAP_ZERO_MEMORY If the reallocation request is for a larger size, this flag specifies that the additional region of memory beyond the original size be initialized to zero. The contents of the memory block up to its original size are unaffected.
  • lpMem
    [in] Pointer to the block of memory that the function reallocates. This pointer is returned by an earlier call to the HeapAlloc or HeapReAlloc function.
  • dwBytes
    [in] Specifies the new size of the memory block, in bytes. A memory block's size can be increased or decreased using this function.

Return Values

If the function fails, it calls SetLastError. An application can call GetLastError for extended error information.

Remarks

If HeapReAlloc succeeds, it allocates at least the amount of memory requested. If the actual amount allocated is greater than the amount requested, the process can use the entire amount. To determine the actual size of the reallocated block, use the HeapSize function.

If HeapReAlloc fails, the original memory is not freed and the original handle and pointer are still valid.

To free a block of memory allocated by HeapReAlloc, use the HeapFree function.

Serialization ensures mutual exclusion when two or more threads attempt to simultaneously allocate or free blocks from the same heap. There is a small performance cost to serialization, but it must be used whenever multiple threads allocate and free memory from the same heap. A critical section is always used to serialize access to an individual heap. There is a critical section per heap to protect access to each heap. An attempt to grab a critical section that is not owned is a fast path operation that incurs little overhead. This would be similar to using the HEAP_NO_SERIALIZE flag if only one thread was ever accessing a particular heap. If there is contention for the critical section, and therefore the heap, a new thread request to allocate heap space will serialize.

Requirements

OS Versions: Windows CE 1.0 and later.
Header: Winbase.h.
Link Library: Coredll.lib.

See Also

GetProcessHeap | HeapAlloc | HeapCreate | HeapDestroy | HeapFree | HeapSize | SetLastError

Last updated on Wednesday, April 13, 2005

© 2005 Microsoft Corporation. All rights reserved.