Snippet: Enable Low Fragmentation Heap for all heaps

最新推荐文章于 2025-08-15 13:27:42 发布

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From matteozan.it

The following code is a code snippet that enable the Low Fragmentation Heap for all heaps. Remembers that a process has at last one heap but for example a CRT console application has practically at last two heaps. The first heap is default heap of process and the second is the CRT heap. If you use a lot of external DLLs is very common that one of this DLL allocate a private heap.

* FLH is useful if a program use intensively Heap memory for a long time, this is the case of a Server application like MySQL.
* This settings is made by the program and affect only itself not all system.

Anyway LFH is enabled by default in Vista.

    1:  // code snippet that try to enable LFH for all heaps of your runnig program.

   2:      HANDLE* hHeaps = NULL;

   3:      int numHeap = GetProcessHeaps(0, NULL);

   4:      if(numHeap > 0)

   5:      {

   6:          ULONG ulEnableLFH = 2;

   7:          hHeaps = (HANDLE*)malloc(sizeof(HANDLE)*numHeap);

   8:          if(GetProcessHeaps(numHeap, hHeaps) == numHeap)

   9:          {

  10:              for(int i = 0; i < numHeap; i++)

  11:              {

  12:                  if(!HeapSetInformation(hHeaps[i], HeapCompatibilityInformation, &ulEnableLFH, sizeof(ulEnableLFH)))

  13:                  {

  14:                      printf("Failed to enable LFH for heap %d.", i);

  15:                  }

  16:              }

  17:          }

  18:          else

  19:          {

  20:              // quite strange !!!

  21:          }

  22:          free(hHeaps);

  23:      }

Suggested reading Windows Internals 4th edition for more details.