原创 uC-GUI 3.24版的内存管理源码分析

/*_CreateHole：整理内存碎片，并申请Size大小的内存 2009.01.16
* Return value:
*   Offset to the memory hole (if available)
*   -1 if not available       */
static GUI_HMEM CreateHole(int Size)
{
  int i, iNext;
  int r = -1;
  for (i=0; (iNext =aBlock.Next) !=0; i= iNext)
  { /*计算两个内存块之间的内存碎片大小  2009.01.16*/
    int NumFreeBytes = aBlock[iNext].Off- (aBlock.Off+aBlock.Size);
    if (NumFreeBytes < Size)
    {
      int NumBytesBeforeBlock = aBlock[iNext].Off - (aBlock.Off+aBlock.Size);
      if (NumBytesBeforeBlock)
      { /*如果两个内存块间存在碎片，则移动内存 2009.01.16 */
        U8* pData = &GUI_Heap.abHeap[aBlock[iNext].Off];
        memmove(pData-NumBytesBeforeBlock, pData, aBlock[iNext].Size);
        aBlock[iNext].Off -=NumBytesBeforeBlock;
      }
    }
  }
/* Check last block */
  if (GUI_ALLOC_SIZE - (aBlock.Off+aBlock.Size) >= Size)
    r = i;
  return r;
}
/*内存分配，返回句柄值，0表示分配失败 2009.01.16 */
static GUI_HMEM _Alloc(int size)
{
  GUI_HMEM hMemNew, hMemIns;
  CheckInit();
  size = Size2LegalSize(size);
  /* Check if memory is available at all ...*/
  if (size > GUI_ALLOC.NumFreeBytes) {
    GUI_DEBUG_WARN1("GUI_ALLOC_Alloc: Insufficient memory configured (Trying to alloc % bytes)", size);
    return 0;
  }
  /* Locate free handle */
  if ((hMemNew = FindFreeHandle()) == 0)
    return 0;
  /* Locate or Create hole of sufficient size */
  hMemIns = FindHole(size);
  #if GUI_ALLOC_AUTDEFRAG
    if (hMemIns == -1) /*内存块都太小，整理内存碎片 2009.01.16*/
    {
      hMemIns = CreateHole(size);
    }
  #endif
/* Occupy hole */
  if (hMemIns==-1) /*内存块分配失败 2009.01.16 */
  {
    GUI_DEBUG_ERROROUT1("GUI_ALLOC_Alloc: Could not allocate %d bytes",size);
    return 0;
  }
  {
   /*计算可以分配的内存实际地址 2009.01.16 */
    int Off = aBlock[hMemIns].Off+aBlock[hMemIns].Size;
    int Next = aBlock[hMemIns].Next;
    aBlock[hMemNew].Size  = size;
    aBlock[hMemNew].Off   = Off;
    /*双链表插入 2009.01.16*/
    if ((aBlock[hMemNew].Next  = Next) >0) {
      aBlock[Next].Prev = hMemNew; 
    }
    aBlock[hMemNew].Prev  = hMemIns;
    aBlock[hMemIns].Next  = hMemNew;
  }
/* Keep track of number of blocks and av. memory */
  GUI_ALLOC.NumUsedBlocks++;
  GUI_ALLOC.NumFreeBlocks--;
  if (GUI_ALLOC.NumFreeBlocksMin > GUI_ALLOC.NumFreeBlocks) {
    GUI_ALLOC.NumFreeBlocksMin = GUI_ALLOC.NumFreeBlocks;
  }
  GUI_ALLOC.NumUsedBytes += size;
  GUI_ALLOC.NumFreeBytes -= size;
  if (GUI_ALLOC.NumFreeBytesMin > GUI_ALLOC.NumFreeBytes) {
    GUI_ALLOC.NumFreeBytesMin = GUI_ALLOC.NumFreeBytes;
  }
/* In order to be on the safe side, zeroinit ! */
  memset(HMEM2PTR(hMemNew), 0, size);
  return hMemNew;
}