VC++中malloc函数源代码
/***
*malloc.c - Get a block of memory from the heap
*
* Copyright (c) 1989-1997, Microsoft Corporation. All rights reserved.
*
*Purpose:
* Defines the malloc() function.
*
*******************************************************************************/
#include <cruntime.h>
#include <malloc.h>
#include <internal.h>
#include <mtdll.h>
#include <dbgint.h>
#ifdef WINHEAP
#include <windows.h>
#include <winheap.h>
#else /* WINHEAP */
#include <heap.h>
#endif /* WINHEAP */
extern int _newmode; /* malloc new() handler mode */
/***
*void *malloc(size_t size) - Get a block of memory from the heap
*
*Purpose:
* Allocate of block of memory of at least size bytes from the heap and
* return a pointer to it.
*
* Calls the new appropriate new handler (if installed).
*
*Entry:
* size_t size - size of block requested
*
*Exit:
* Success: Pointer to memory block
* Failure: NULL (or some error value)
*
*Uses:
*
*Exceptions:
*
*******************************************************************************/
void * __cdecl _malloc_base (size_t size)
{
return _nh_malloc_base(size, _newmode);
}
/***
*void *_nh_malloc_base(size_t size) - Get a block of memory from the heap
*
*Purpose:
* Allocate of block of memory of at least size bytes from the heap and
* return a pointer to it.
*
* Calls the appropriate new handler (if installed).
*
* There are two distinct new handler schemes supported. The 'new' ANSI
* C++ scheme overrides the 'old' scheme when it is activated. A value of
* _NOPTH for the 'new' handler indicates that it is inactivated and the
* 'old' handler is then called.
*
*Entry:
* size_t size - size of block requested
*
*Exit:
* Success: Pointer to memory block
* Failure: NULL (or some error value)
*
*Uses:
*
*Exceptions:
*
*******************************************************************************/
void * __cdecl _nh_malloc_base (size_t size, int nhFlag)
{
void * pvReturn;
// validate size
if (size > _HEAP_MAXREQ)
return NULL;
#ifndef WINHEAP
/* round requested size */
size = _ROUND2(size, _GRANULARITY);
#endif /* WINHEAP */
for (;;) {
// allocate memory block
if (size <= _HEAP_MAXREQ)
pvReturn = _heap_alloc_base(size);
else
pvReturn = NULL;
// if successful allocation, return pointer to memory
// if new handling turned off altogether, return NULL
if (pvReturn || nhFlag == 0)
return pvReturn;
// call installed new handler
if (!_callnewh(size))
return NULL;
// new handler was successful -- try to allocate again
}
}
/***
*void *_heap_alloc_base(size_t size) - does actual allocation
*
*Purpose:
* Same as malloc() except the new handler is not called.
*
*Entry:
* See malloc
*
*Exit:
* See malloc
*
*Exceptions:
*
*******************************************************************************/
void * __cdecl _heap_alloc_base (size_t size)
{
#ifdef WINHEAP
void * pvReturn;
#else /* WINHEAP */
_PBLKDESC pdesc;
_PBLKDESC pdesc2;
#endif /* WINHEAP */
#ifdef WINHEAP
if (size <= __sbh_threshold)
{
_mlock(_HEAP_LOCK);
pvReturn = __sbh_alloc_block(size);
_munlock(_HEAP_LOCK);
if (pvReturn)
return pvReturn;
}
if (size == 0)
size = 1;
size = (size + BYTES_PER_PARA - 1) & ~(BYTES_PER_PARA - 1);
return HeapAlloc(_crtheap, 0, size);
}
#else /* WINHEAP */
/* try to find a big enough free block
*/
if ( (pdesc = _heap_search(size)) == NULL )
{
if ( _heap_grow(size) != -1 )
{
/* try finding a big enough free block again. the
* success of the call to _heap_grow should guarantee
* it, but...
*/
if ( (pdesc = _heap_search(size)) == NULL )
{
/* something unexpected, and very bad, has
* happened. abort!
*/
_heap_abort();
}
}
else
return NULL;
}
/* carve the block into two pieces (if necessary). the first piece
* shall be of the exact requested size, marked inuse and returned to
* the caller. the leftover piece is to be marked free.
*/
if ( _BLKSIZE(pdesc) != size ) {
/* split up the block and free the leftover piece back to
* the heap
*/
if ( (pdesc2 = _heap_split_block(pdesc, size)) != NULL )
_SET_FREE(pdesc2);
}
/* mark pdesc inuse
*/
_SET_INUSE(pdesc);
/* check proverdesc and reset, if necessary
*/
_heap_desc.proverdesc = pdesc->pnextdesc;
return( (void *)((char *)_ADDRESS(pdesc) + _HDRSIZE) );
}
/***
*_PBLKDESC _heap_split_block(pdesc, newsize) - split a heap allocation block
* into two allocation blocks
*
*Purpose:
* Split the allocation block described by pdesc into two blocks, the
* first one being of newsize bytes.
*
* Notes: It is caller's responsibilty to set the status (i.e., free
* or inuse) of the two new blocks, and to check and reset proverdesc
* if necessary. See Exceptions (below) for additional requirements.
*
*Entry:
* _PBLKDESC pdesc - pointer to the allocation block descriptor
* size_t newsize - size for the first of the two sub-blocks (i.e.,
* (i.e., newsize == _BLKSIZE(pdesc), on exit)
*
*Exit:
* If successful, return a pointer to the descriptor for the leftover
* block.
* Otherwise, return NULL.
*
*Exceptions:
* It is assumed pdesc points to a valid allocation block descriptor and
* newsize is a valid heap block size as is (i.e., WITHOUT rounding). If
* either of these of assumption is violated, _heap_split_block() will
* likely corrupt the heap. Note also that _heap_split_block will simply
* return to the caller if newsize >= _BLKSIZE(pdesc), on entry.
*
*******************************************************************************/
_PBLKDESC __cdecl _heap_split_block (
REG1 _PBLKDESC pdesc,
size_t newsize
)
{
REG2 _PBLKDESC pdesc2;
_ASSERTE(("_heap_split_block: bad pdesc arg", _CHECK_PDESC(pdesc)));
_ASSERTE(("_heap_split_block: bad newsize arg", _ROUND2(newsize,_GRANULARITY) == newsize));
/* carve the block into two pieces (if possible). the first piece
* is to be exactly newsize bytes.
*/
if ( (_BLKSIZE(pdesc) > newsize) && ((pdesc2 = __getempty())
!= NULL) )
{
/* set it up to manage the second piece and link it in to
* the list
*/
pdesc2->pblock = (void *)((char *)_ADDRESS(pdesc) + newsize +
_HDRSIZE);
*(void **)(pdesc2->pblock) = pdesc2;
pdesc2->pnextdesc = pdesc->pnextdesc;
pdesc->pnextdesc = pdesc2;
return pdesc2;
}
return NULL;
}
#endif /* WINHEAP */
