Snippet: Enable Low Fragmentation Heap for all heaps

From matteozan.it

 

The following code is a code snippet that enable the LowFragmentation Heap for all heaps. Remembers that a process has at lastone heap but for example a CRT console application has practically atlast two heaps. The first heap is default heap of process and thesecond is the CRT heap. If you use a lot of external DLLs is verycommon 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.