expand.c

来自「vc6.0完整版」· C语言 代码 · 共 158 行

/***
*expand.c - Win32 expand heap routine
*
*       Copyright (c) 1991-1998, Microsoft Corporation. All rights reserved.
*
*Purpose:
*
*******************************************************************************/

#ifdef WINHEAP

#include <cruntime.h>
#include <malloc.h>
#include <winheap.h>
#include <windows.h>
#include <mtdll.h>
#include <dbgint.h>

/***
*void *_expand(void *pblck, size_t newsize) - expand/contract a block of memory
*       in the heap
*
*Purpose:
*       Resizes a block in the heap to newsize bytes. newsize may be either
*       greater (expansion) or less (contraction) than the original size of
*       the block. The block is NOT moved.
*
*       NOTES:
*
*       (1) In this implementation, if the block cannot be grown to the
*       desired size, the resulting block will NOT be grown to the max
*       possible size.  (That is, either it works or it doesn't.)
*
*       (2) Unlike other implementations, you can NOT pass a previously
*       freed block to this routine and expect it to work.
*
*Entry:
*       void *pblck - pointer to block in the heap previously allocated
*                 by a call to malloc(), realloc() or _expand().
*
*       size_t newsize  - requested size for the resized block
*
*Exit:
*       Success:  Pointer to the resized memory block (i.e., pblck)
*       Failure:  NULL
*
*Uses:
*
*Exceptions:
*       If pblck does not point to a valid allocation block in the heap,
*       _expand() will behave unpredictably and probably corrupt the heap.
*
*******************************************************************************/

void * __cdecl _expand_base (void * pBlock, size_t newsize)
{
        PHEADER     pHeader;
        void *      pvReturn;


        /* validate size */
        if ( newsize > _HEAP_MAXREQ )
            return NULL;

        if ( __active_heap == __V6_HEAP )
        {
#ifdef _MT
            _mlock( _HEAP_LOCK );
            __try {
#endif  /* _MT */

            //  if allocation block lies within the small-block heap,
            //  try to resize it there
            if ((pHeader = __sbh_find_block(pBlock)) != NULL)
            {
                pvReturn = NULL;
                if ( (newsize <= __sbh_threshold) &&
                     __sbh_resize_block(pHeader, pBlock, newsize) )
                    pvReturn = pBlock;
            }

#ifdef _MT
            }
            __finally {
                _munlock( _HEAP_LOCK );
            }
#endif  /* _MT */

            if ( pHeader == NULL )
            {
                //  force nonzero size and round up to next paragraph
                if (newsize == 0)
                    newsize = 1;
                newsize = (newsize + BYTES_PER_PARA - 1) & ~(BYTES_PER_PARA - 1);

                pvReturn = HeapReAlloc(_crtheap, HEAP_REALLOC_IN_PLACE_ONLY,
                                       pBlock, newsize);
            }
        }
        else if ( __active_heap == __V5_HEAP )
        {
            __old_sbh_region_t *preg;
            __old_sbh_page_t *  ppage;
            __old_page_map_t *  pmap;

            //  force nonzero size and round up to next paragraph
            if (newsize == 0)
                newsize = 1;
            newsize = (newsize + _OLD_PARASIZE - 1) & ~(_OLD_PARASIZE - 1);
#ifdef _MT
            _mlock(_HEAP_LOCK);
            __try {
#endif  /* _MT */
            pmap = __old_sbh_find_block(pBlock, &preg, &ppage);

            //  allocation block lies within the small-block heap, try to resize
            //  it there.
            if ( pmap != NULL )
            {
                //  *pBlock lies within the small-block heap, try to resize it
                //  there
                pvReturn = NULL;
                if ( (newsize <= __old_sbh_threshold) &&
                     __old_sbh_resize_block(preg, ppage, pmap,
                                            newsize >> _OLD_PARASHIFT) )
                    pvReturn = pBlock;
                return pvReturn;
            }

#ifdef _MT
            }
            __finally {
                _munlock(_HEAP_LOCK);
            }
#endif  /* _MT */

            if ( pmap == NULL )
                pvReturn = HeapReAlloc(_crtheap, HEAP_REALLOC_IN_PLACE_ONLY,
                                       pBlock, newsize);
        }
        else    // __active_heap == __SYSTEM_HEAP
        {
            //  force nonzero size and round up to next paragraph
            if (newsize == 0)
                newsize = 1;
            newsize = (newsize + BYTES_PER_PARA - 1) & ~(BYTES_PER_PARA - 1);

            pvReturn = HeapReAlloc(_crtheap, HEAP_REALLOC_IN_PLACE_ONLY,
                                   pBlock, newsize);

        }

        return pvReturn;
}


#endif  /* WINHEAP */