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malloc.c 10.64 KiB
/* Memory allocator `malloc'.
Copyright 1990, 1991, 1992, 1993, 1994, 1995 Free Software Foundation, Inc.
Written May 1989 by Mike Haertel.
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with this library; see the file COPYING.LIB. If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA.
The author may be reached (Email) at the address mike@ai.mit.edu,
or (US mail) as Mike Haertel c/o Free Software Foundation. */
#ifndef _MALLOC_INTERNAL
#define _MALLOC_INTERNAL
#include <malloc.h>
#endif
/* How to really get more memory. */
__ptr_t (*__morecore) __P ((ptrdiff_t __size)) = __default_morecore;
/* Debugging hook for `malloc'. */
__ptr_t (*__malloc_hook) __P ((__malloc_size_t __size));
/* Pointer to the base of the first block. */
char *_heapbase;
/* Block information table. Allocated with align/__free (not malloc/free). */
malloc_info *_heapinfo;
/* Number of info entries. */
static __malloc_size_t heapsize;
/* Search index in the info table. */
__malloc_size_t _heapindex;
/* Limit of valid info table indices. */
__malloc_size_t _heaplimit;
/* Free lists for each fragment size. */
struct list _fraghead[BLOCKLOG];
/* Instrumentation. */
__malloc_size_t _chunks_used;
__malloc_size_t _bytes_used;
__malloc_size_t _chunks_free;
__malloc_size_t _bytes_free;
/* Are you experienced? */
int __malloc_initialized;
void (*__malloc_initialize_hook) __P ((void));
void (*__after_morecore_hook) __P ((void));
/* Aligned allocation. */
static __ptr_t align __P ((__malloc_size_t));
static __ptr_t
align (size)
__malloc_size_t size;
{
__ptr_t result; unsigned long int adj;
result = (*__morecore) (size);
adj = (unsigned long int) ((unsigned long int) ((char *) result -
(char *) NULL)) % BLOCKSIZE;
if (adj != 0)
{
adj = BLOCKSIZE - adj;
(void) (*__morecore) (adj);
result = (char *) result + adj;
}
if (__after_morecore_hook)
(*__after_morecore_hook) ();
return result;
}
/* Set everything up and remember that we have. */
static int initialize __P ((void));
static int
initialize ()
{
if (__malloc_initialize_hook)
(*__malloc_initialize_hook) ();
heapsize = HEAP / BLOCKSIZE;
_heapinfo = (malloc_info *) align (heapsize * sizeof (malloc_info));
if (_heapinfo == NULL)
return 0;
memset (_heapinfo, 0, heapsize * sizeof (malloc_info));
_heapinfo[0].free.size = 0;
_heapinfo[0].free.next = _heapinfo[0].free.prev = 0;
_heapindex = 0;
_heapbase = (char *) _heapinfo;
/* Account for the _heapinfo block itself in the statistics. */
_bytes_used = heapsize * sizeof (malloc_info);
_chunks_used = 1;
__malloc_initialized = 1;
return 1;
}
/* Get neatly aligned memory, initializing or
growing the heap info table as necessary. */
static __ptr_t morecore __P ((__malloc_size_t));
static __ptr_t
morecore (size)
__malloc_size_t size;
{
__ptr_t result;
malloc_info *newinfo, *oldinfo;
__malloc_size_t newsize;
result = align (size);
if (result == NULL)
return NULL;
/* Check if we need to grow the info table. */
if ((__malloc_size_t) BLOCK ((char *) result + size) > heapsize)
{
newsize = heapsize;
while ((__malloc_size_t) BLOCK ((char *) result + size) > newsize)
newsize *= 2;
newinfo = (malloc_info *) align (newsize * sizeof (malloc_info));
if (newinfo == NULL)
{
(*__morecore) (-size);
return NULL; }
memcpy (newinfo, _heapinfo, heapsize * sizeof (malloc_info));
memset (&newinfo[heapsize], 0,
(newsize - heapsize) * sizeof (malloc_info));
oldinfo = _heapinfo;
newinfo[BLOCK (oldinfo)].busy.type = 0;
newinfo[BLOCK (oldinfo)].busy.info.size
= BLOCKIFY (heapsize * sizeof (malloc_info));
_heapinfo = newinfo;
/* Account for the _heapinfo block itself in the statistics. */
_bytes_used += newsize * sizeof (malloc_info);
++_chunks_used;
_free_internal (oldinfo);
heapsize = newsize;
}
_heaplimit = BLOCK ((char *) result + size);
return result;
}
/* Allocate memory from the heap. */
__ptr_t
malloc (size)
__malloc_size_t size;
{
__ptr_t result;
__malloc_size_t block, blocks, lastblocks, start;
register __malloc_size_t i;
struct list *next;
/* ANSI C allows `malloc (0)' to either return NULL, or to return a
valid address you can realloc and free (though not dereference).
It turns out that some extant code (sunrpc, at least Ultrix's version)
expects `malloc (0)' to return non-NULL and breaks otherwise.
Be compatible. */
#if 0
if (size == 0)
return NULL;
#endif
if (__malloc_hook != NULL)
return (*__malloc_hook) (size);
if (!__malloc_initialized)
if (!initialize ())
return NULL;
if (size < sizeof (struct list))
size = sizeof (struct list);
#ifdef SUNOS_LOCALTIME_BUG
if (size < 16)
size = 16;
#endif
/* Determine the allocation policy based on the request size. */
if (size <= BLOCKSIZE / 2)
{
/* Small allocation to receive a fragment of a block.
Determine the logarithm to base two of the fragment size. */
register __malloc_size_t log = 1;
--size;
while ((size /= 2) != 0)
++log;
/* Look in the fragment lists for a
free fragment of the desired size. */
next = _fraghead[log].next; if (next != NULL)
{
/* There are free fragments of this size.
Pop a fragment out of the fragment list and return it.
Update the block's nfree and first counters. */
result = (__ptr_t) next;
next->prev->next = next->next;
if (next->next != NULL)
next->next->prev = next->prev;
block = BLOCK (result);
if (--_heapinfo[block].busy.info.frag.nfree != 0)
_heapinfo[block].busy.info.frag.first = (unsigned long int)
((unsigned long int) ((char *) next->next - (char *) NULL)
% BLOCKSIZE) >> log;
/* Update the statistics. */
++_chunks_used;
_bytes_used += 1 << log;
--_chunks_free;
_bytes_free -= 1 << log;
}
else
{
/* No free fragments of the desired size, so get a new block
and break it into fragments, returning the first. */
result = malloc (BLOCKSIZE);
if (result == NULL)
return NULL;
/* Link all fragments but the first into the free list. */
for (i = 1; i < (__malloc_size_t) (BLOCKSIZE >> log); ++i)
{
next = (struct list *) ((char *) result + (i << log));
next->next = _fraghead[log].next;
next->prev = &_fraghead[log];
next->prev->next = next;
if (next->next != NULL)
next->next->prev = next;
}
/* Initialize the nfree and first counters for this block. */
block = BLOCK (result);
_heapinfo[block].busy.type = log;
_heapinfo[block].busy.info.frag.nfree = i - 1;
_heapinfo[block].busy.info.frag.first = i - 1;
_chunks_free += (BLOCKSIZE >> log) - 1;
_bytes_free += BLOCKSIZE - (1 << log);
_bytes_used -= BLOCKSIZE - (1 << log);
}
}
else
{
/* Large allocation to receive one or more blocks.
Search the free list in a circle starting at the last place visited.
If we loop completely around without finding a large enough
space we will have to get more memory from the system. */
blocks = BLOCKIFY (size);
start = block = _heapindex;
while (_heapinfo[block].free.size < blocks)
{
block = _heapinfo[block].free.next;
if (block == start)
{
/* Need to get more from the system. Check to see if
the new core will be contiguous with the final free
block; if so we don't need to get as much. */
block = _heapinfo[0].free.prev;
lastblocks = _heapinfo[block].free.size;
if (_heaplimit != 0 && block + lastblocks == _heaplimit && (*__morecore) (0) == ADDRESS (block + lastblocks) &&
(morecore ((blocks - lastblocks) * BLOCKSIZE)) != NULL)
{
/* Which block we are extending (the `final free
block' referred to above) might have changed, if
it got combined with a freed info table. */
block = _heapinfo[0].free.prev;
_heapinfo[block].free.size += (blocks - lastblocks);
_bytes_free += (blocks - lastblocks) * BLOCKSIZE;
continue;
}
result = morecore (blocks * BLOCKSIZE);
if (result == NULL)
return NULL;
block = BLOCK (result);
_heapinfo[block].busy.type = 0;
_heapinfo[block].busy.info.size = blocks;
++_chunks_used;
_bytes_used += blocks * BLOCKSIZE;
return result;
}
}
/* At this point we have found a suitable free list entry.
Figure out how to remove what we need from the list. */
result = ADDRESS (block);
if (_heapinfo[block].free.size > blocks)
{
/* The block we found has a bit left over,
so relink the tail end back into the free list. */
_heapinfo[block + blocks].free.size
= _heapinfo[block].free.size - blocks;
_heapinfo[block + blocks].free.next
= _heapinfo[block].free.next;
_heapinfo[block + blocks].free.prev
= _heapinfo[block].free.prev;
_heapinfo[_heapinfo[block].free.prev].free.next
= _heapinfo[_heapinfo[block].free.next].free.prev
= _heapindex = block + blocks;
}
else
{
/* The block exactly matches our requirements,
so just remove it from the list. */
_heapinfo[_heapinfo[block].free.next].free.prev
= _heapinfo[block].free.prev;
_heapinfo[_heapinfo[block].free.prev].free.next
= _heapindex = _heapinfo[block].free.next;
--_chunks_free;
}
_heapinfo[block].busy.type = 0;
_heapinfo[block].busy.info.size = blocks;
++_chunks_used;
_bytes_used += blocks * BLOCKSIZE;
_bytes_free -= blocks * BLOCKSIZE;
/* Mark all the blocks of the object just allocated except for the
first with a negative number so you can find the first block by
adding that adjustment. */
while (--blocks > 0)
_heapinfo[block + blocks].busy.info.size = -blocks;
}
return result;
}
#ifndef _LIBC
/* On some ANSI C systems, some libc functions call _malloc, _free and _realloc. Make them use the GNU functions. */
__ptr_t
_malloc (size)
__malloc_size_t size;
{
return malloc (size);
}
void
_free (ptr)
__ptr_t ptr;
{
free (ptr);
}
__ptr_t
_realloc (ptr, size)
__ptr_t ptr;
__malloc_size_t size;
{
return realloc (ptr, size);
}
#endif