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git-svn-id: https://nuttx.svn.sourceforge.net/svnroot/nuttx/trunk@2342 7fd9a85b-ad96-42d3-883c-3090e2eb8679
153 lines
5 KiB
C
153 lines
5 KiB
C
/************************************************************************
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* mm/mm_free.c
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*
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* Copyright (C) 2007, 2009 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <spudmonkey@racsa.co.cr>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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************************************************************************/
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/************************************************************************
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* Included Files
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************************************************************************/
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#include <assert.h>
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#include "mm_environment.h"
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#include "mm_internal.h"
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/************************************************************************
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* Pre-processor Definitions
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************************************************************************/
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/************************************************************************
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* Private Functions
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************************************************************************/
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/************************************************************************
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* Public Functions
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************************************************************************/
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/************************************************************************
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* free
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*
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* Description:
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* Returns a chunk of memory into the list of free nodes,
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* merging with adjacent free chunks if possible.
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*
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************************************************************************/
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void free(FAR void *mem)
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{
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FAR struct mm_freenode_s *node;
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FAR struct mm_freenode_s *prev;
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FAR struct mm_freenode_s *next;
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mvdbg("Freeing %p\n", mem);
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/* Protect against attempts to free a NULL reference */
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if (!mem)
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{
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return;
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}
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/* We need to hold the MM semaphore while we muck with the
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* nodelist.
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*/
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mm_takesemaphore();
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/* Map the memory chunk into a free node */
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node = (FAR struct mm_freenode_s *)((char*)mem - SIZEOF_MM_ALLOCNODE);
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node->preceding &= ~MM_ALLOC_BIT;
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/* Check if the following node is free and, if so, merge it */
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next = (FAR struct mm_freenode_s *)((char*)node + node->size);
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if ((next->preceding & MM_ALLOC_BIT) == 0)
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{
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FAR struct mm_allocnode_s *andbeyond;
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/* Get the node following the next node (which will
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* become the new next node). We know that we can never
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* index past the tail chunk because it is always allocated.
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*/
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andbeyond = (FAR struct mm_allocnode_s*)((char*)next + next->size);
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/* Remove the next node. There must be a predecessor,
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* but there may not be a successor node.
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*/
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DEBUGASSERT(next->blink);
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next->blink->flink = next->flink;
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if (next->flink)
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{
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next->flink->blink = next->blink;
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}
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/* Then merge the two chunks */
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node->size += next->size;
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andbeyond->preceding = node->size | (andbeyond->preceding & MM_ALLOC_BIT);
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next = (FAR struct mm_freenode_s *)andbeyond;
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}
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/* Check if the preceding node is also free and, if so, merge
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* it with this node
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*/
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prev = (FAR struct mm_freenode_s *)((char*)node - node->preceding);
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if ((prev->preceding & MM_ALLOC_BIT) == 0)
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{
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/* Remove the node. There must be a predecessor, but there may
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* not be a successor node.
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*/
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DEBUGASSERT(prev->blink);
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prev->blink->flink = prev->flink;
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if (prev->flink)
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{
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prev->flink->blink = prev->blink;
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}
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/* Then merge the two chunks */
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prev->size += node->size;
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next->preceding = prev->size | (next->preceding & MM_ALLOC_BIT);
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node = prev;
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}
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/* Add the merged node to the nodelist */
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mm_addfreechunk(node);
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mm_givesemaphore();
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}
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