sergiotarxz/nuttx
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity
f4a374b6d9
nuttx/mm/mm_heap/mm_realloc.c

365 lines
10 KiB
C
Raw Blame History

/****************************************************************************
* mm/mm_heap/mm_realloc.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <assert.h>
#include <nuttx/mm/mm.h>
#include "mm_heap/mm.h"
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: mm_realloc
*
* Description:
* If the reallocation is for less space, then:
*
* (1) the current allocation is reduced in size
* (2) the remainder at the end of the allocation is returned to the
* free list.
*
* If the request is for more space and the current allocation can be
* extended, it will be extended by:
*
* (1) Taking the additional space from the following free chunk, or
* (2) Taking the additional space from the preceding free chunk.
* (3) Or both
*
* If the request is for more space but the current chunk cannot be
* extended, then malloc a new buffer, copy the data into the new buffer,
* and free the old buffer.
*
****************************************************************************/
FAR void *mm_realloc(FAR struct mm_heap_s *heap, FAR void *oldmem,
size_t size)
{
FAR struct mm_allocnode_s *oldnode;
FAR struct mm_freenode_s *prev;
FAR struct mm_freenode_s *next;
size_t newsize;
size_t oldsize;
size_t prevsize = 0;
size_t nextsize = 0;
FAR void *newmem;
/* If oldmem is NULL, then realloc is equivalent to malloc */
if (oldmem == NULL)
{
return mm_malloc(heap, size);
}
/* If size is zero, then realloc is equivalent to free */
if (size < 1)
{
mm_free(heap, oldmem);
return NULL;
}
/* Adjust the size to account for (1) the size of the allocated node and
* (2) to make sure that it is an even multiple of our granule size.
*/
newsize = MM_ALIGN_UP(size + SIZEOF_MM_ALLOCNODE);
if (newsize < size)
{
/* There must have been an integer overflow */
DEBUGASSERT(false);
return NULL;
}
/* Map the memory chunk into an allocated node structure */
oldnode = (FAR struct mm_allocnode_s *)
((FAR char *)oldmem - SIZEOF_MM_ALLOCNODE);
/* We need to hold the MM semaphore while we muck with the nodelist. */
mm_takesemaphore(heap);
DEBUGASSERT(oldnode->preceding & MM_ALLOC_BIT);
DEBUGASSERT(mm_heapmember(heap, oldmem));
/* Check if this is a request to reduce the size of the allocation. */
oldsize = oldnode->size;
if (newsize <= oldsize)
{
/* Handle the special case where we are not going to change the size
* of the allocation.
*/
if (newsize < oldsize)
{
mm_shrinkchunk(heap, oldnode, newsize);
}
/* Then return the original address */
mm_givesemaphore(heap);
return oldmem;
}
/* This is a request to increase the size of the allocation, Get the
* available sizes before and after the oldnode so that we can make the
* best decision
*/
next = (FAR struct mm_freenode_s *)
((FAR char *)oldnode + oldnode->size);
if ((next->preceding & MM_ALLOC_BIT) == 0)
{
nextsize = next->size;
}
prev = (FAR struct mm_freenode_s *)
((FAR char *)oldnode - (oldnode->preceding & ~MM_ALLOC_BIT));
if ((prev->preceding & MM_ALLOC_BIT) == 0)
{
prevsize = prev->size;
}
/* Now, check if we can extend the current allocation or not */
if (nextsize + prevsize + oldsize >= newsize)
{
size_t needed = newsize - oldsize;
size_t takeprev = 0;
size_t takenext = 0;
/* Check if we can extend into the previous chunk and if the
* previous chunk is smaller than the next chunk.
*/
if (prevsize > 0 && (nextsize >= prevsize || nextsize < 1))
{
/* Can we get everything we need from the previous chunk? */
if (needed > prevsize)
{
/* No, take the whole previous chunk and get the
* rest that we need from the next chunk.
*/
takeprev = prevsize;
takenext = needed - prevsize;
}
else
{
/* Yes, take what we need from the previous chunk */
takeprev = needed;
takenext = 0;
}
needed = 0;
}
/* Check if we can extend into the next chunk and if we still need
* more memory.
*/
if (nextsize > 0 && needed)
{
/* Can we get everything we need from the next chunk? */
if (needed > nextsize)
{
/* No, take the whole next chunk and get the rest that we
* need from the previous chunk.
*/
takeprev = needed - nextsize;
takenext = nextsize;
}
else
{
/* Yes, take what we need from the previous chunk */
takeprev = 0;
takenext = needed;
}
}
/* Extend into the previous free chunk */
newmem = oldmem;
if (takeprev)
{
FAR struct mm_allocnode_s *newnode;
/* Remove the previous node. There must be a predecessor, but
* there may not be a successor node.
*/
DEBUGASSERT(prev->blink);
prev->blink->flink = prev->flink;
if (prev->flink)
{
prev->flink->blink = prev->blink;
}
/* Extend the node into the previous free chunk */
newnode = (FAR struct mm_allocnode_s *)
((FAR char *)oldnode - takeprev);
/* Did we consume the entire preceding chunk? */
if (takeprev < prevsize)
{
/* No.. just take what we need from the previous chunk and put
* it back into the free list
*/
prev->size -= takeprev;
DEBUGASSERT(prev->size >= SIZEOF_MM_FREENODE);
newnode->size = oldsize + takeprev;
newnode->preceding = prev->size | MM_ALLOC_BIT;
next->preceding = newnode->size |
(next->preceding & MM_ALLOC_BIT);
/* Return the previous free node to the nodelist
* (with the new size)
*/
mm_addfreechunk(heap, prev);
}
else
{
/* Yes.. update its size (newnode->preceding is already set) */
newnode->size += oldsize;
newnode->preceding |= MM_ALLOC_BIT;
next->preceding = newnode->size |
(next->preceding & MM_ALLOC_BIT);
}
/* Now we have to move the user contents 'down' in memory. memcpy
* should be safe for this.
*/
newmem = (FAR void *)((FAR char *)newnode + SIZEOF_MM_ALLOCNODE);
memcpy(newmem, oldmem, oldsize - SIZEOF_MM_ALLOCNODE);
/* Now we want to return newnode */
oldnode = newnode;
oldsize = newnode->size;
}
/* Extend into the next free chunk */
if (takenext)
{
FAR struct mm_freenode_s *newnode;
FAR struct mm_allocnode_s *andbeyond;
/* Get the chunk following the next node (which could be the tail
* chunk)
*/
andbeyond = (FAR struct mm_allocnode_s *)
((FAR char *)next + nextsize);
/* Remove the next node. There must be a predecessor, but there
* may not be a successor node.
*/
DEBUGASSERT(next->blink);
next->blink->flink = next->flink;
if (next->flink)
{
next->flink->blink = next->blink;
}
/* Extend the node into the next chunk */
oldnode->size = oldsize + takenext;
newnode = (FAR struct mm_freenode_s *)
((FAR char *)oldnode + oldnode->size);
/* Did we consume the entire preceding chunk? */
if (takenext < nextsize)
{
/* No, take what we need from the next chunk and return it to
* the free nodelist.
*/
newnode->size = nextsize - takenext;
DEBUGASSERT(newnode->size >= SIZEOF_MM_FREENODE);
newnode->preceding = oldnode->size;
andbeyond->preceding = newnode->size |
(andbeyond->preceding & MM_ALLOC_BIT);
/* Add the new free node to the nodelist (with the new size) */
mm_addfreechunk(heap, newnode);
}
else
{
/* Yes, just update some pointers. */
andbeyond->preceding = oldnode->size |
(andbeyond->preceding & MM_ALLOC_BIT);
}
}
mm_givesemaphore(heap);
return newmem;
}
/* The current chunk cannot be extended.
* Just allocate a new chunk and copy
*/
else
{
/* Allocate a new block. On failure, realloc must return NULL but
* leave the original memory in place.
*/
mm_givesemaphore(heap);
newmem = (FAR void *)mm_malloc(heap, size);
if (newmem)
{
memcpy(newmem, oldmem, oldsize);
mm_free(heap, oldmem);
}
return newmem;
}
}
Reference in New Issue View Git Blame Copy Permalink