heapsrch.c

C标准库源代码

/***
*heapsrch.c - search the heap for a free block
*
*       Copyright (c) 1989-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
*       Defines the _heap_search() function.
*
*******************************************************************************/


#ifndef WINHEAP


#include <cruntime.h>
#include <heap.h>
#include <stddef.h>

#define LOOP_FOREVER    while(1)

/***
*_PBLKDESC _heap_search(unsigned size) - Find a free block of a least size
*       bytes.
*
*Purpose:
*       Finds a free block of at least size bytes. Searches the list of block
*       descriptors from *proverdesc to the end (marked by the sentinel). The
*       search is strictly first fit. Adjacent free blocks are coalesced as
*       they are encountered during the search.
*
*Entry:
*       unsigned size   - size of block requested
*
*Exit:
*       Success:  Pointer to descriptor for free memory block of at least size
*               bytes
*       Failure:  NULL
*
*Uses:
*
*Exceptions:
*
*******************************************************************************/

_PBLKDESC __cdecl _heap_search (
        unsigned size
        )
{
        REG1 _PBLKDESC pdesc;
        REG2 _PBLKDESC pdesc2;
        _PBLKDESC pretdesc = NULL;

        /* search from proverdesc thru plastdesc, looking for free block of
         * at least size bytes. coalesce adjacent free blocks during the
         * search. the search is strictly first fit. that is, it terminates
         * when the first block is found of adequate size.
         */
        for ( pdesc = _heap_desc.proverdesc ; pdesc != &(_heap_desc.sentinel) ;
        pdesc = pdesc->pnextdesc )
                /* is pdesc free?
                 */
                if ( _IS_FREE(pdesc) )
                        /* coalesce loop
                         */
                        LOOP_FOREVER {
                                /* if pdesc is big enough, return it
                                 */
                                if ( _BLKSIZE(pdesc) >= size ) {
                                        pretdesc = pdesc;
                                        goto searchdone;
                                }

                                /* see if the next block is free and, if so,
                                 * coalesce it with pdesc
                                 */
                                pdesc2 = pdesc->pnextdesc;
                                if ( _IS_FREE(pdesc2) ) {
                                        /* coalesce pdesc2 with pdesc
                                         */
                                        pdesc->pnextdesc = pdesc2->pnextdesc;
                                        _PUTEMPTY(pdesc2);
                                }
                                else
                                        break;
                        } /* end LOOP_FOREVER */

        for ( pdesc = _heap_desc.pfirstdesc ; pdesc != _heap_desc.proverdesc ;
        pdesc = pdesc->pnextdesc )
                /* is pdesc free?
                 */
                if ( _IS_FREE(pdesc) )
                        /* coalesce loop
                         */
                        LOOP_FOREVER {
                                /* if pdesc is big enough, return it
                                 */
                                if ( _BLKSIZE(pdesc) >= size ) {
                                        pretdesc = pdesc;
                                        goto searchdone;
                                }

                                /* see if the next block is free and, if so,
                                 * coalesce it with pdesc
                                 */
                                pdesc2 = pdesc->pnextdesc;
                                if ( _IS_FREE(pdesc2) ) {
                                        /* coalesce pdesc2 with pdesc
                                         */
                                        pdesc->pnextdesc = pdesc2->pnextdesc;
                                        _PUTEMPTY(pdesc2);

                                        /* special handling for the case where
                                         * the rover has been coalesced (search
                                         * ends)
                                         */
                                        if ( _heap_desc.proverdesc == pdesc2 )
                                        {
                                                _heap_desc.proverdesc = pdesc;
                                                if ( _BLKSIZE(pdesc) >= size )
                                                        pretdesc = pdesc;
                                                goto searchdone;
                                        }
                                }
                                else
                                        break;
                        } /* end LOOP_FOREVER */

searchdone:

        /* common exit for all code paths. win, lose or draw, this is the
         * only code path back to the caller.
         */
        return(pretdesc);
}


#endif  /* WINHEAP */