HeapReAlloc

A version of this page is also available for

Windows Embedded CE 6.0 R3

4/8/2010

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

Syntax

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] 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. Do not specify this flag when accessing the process heap. The system might 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 might 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] Valid 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] Size of the new memory block, in bytes.

  A memory block's size can be increased or decreased using this function.

Return Value

A pointer to the allocated memory block indicates success. Pointers returned by HeapAlloc and HeapReAlloc are valid pointers until they are freed by HeapFree.

Call GetLastError to get extended error information.

Remarks

If HeapReAlloc succeeds, it allocates at least the amount of memory requested. If the 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, but it must be used when 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 is 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

See Also

Reference

Memory Management Functions
GetProcessHeap
HeapAlloc
HeapCreate
HeapDestroy
HeapFree
HeapSize
SetLastError