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Diffstat (limited to 'nuttx/mm/mm_free.c')
| -rw-r--r-- | nuttx/mm/mm_free.c | 153 |
1 files changed, 153 insertions, 0 deletions
diff --git a/nuttx/mm/mm_free.c b/nuttx/mm/mm_free.c new file mode 100644 index 000000000..b34b8a459 --- /dev/null +++ b/nuttx/mm/mm_free.c @@ -0,0 +1,153 @@ +/**************************************************************************** + * mm/mm_free.c + * + * Copyright (C) 2007, 2009 Gregory Nutt. All rights reserved. + * Author: Gregory Nutt <gnutt@nuttx.org> + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in + * the documentation and/or other materials provided with the + * distribution. + * 3. Neither the name NuttX nor the names of its contributors may be + * used to endorse or promote products derived from this software + * without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS + * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE + * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, + * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS + * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED + * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN + * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE + * POSSIBILITY OF SUCH DAMAGE. + * + ****************************************************************************/ + +/**************************************************************************** + * Included Files + ****************************************************************************/ + +#include <assert.h> + +#include "mm_environment.h" +#include "mm_internal.h" + +/**************************************************************************** + * Pre-processor Definitions + ****************************************************************************/ + +/**************************************************************************** + * Private Functions + ****************************************************************************/ + +/**************************************************************************** + * Public Functions + ****************************************************************************/ + +/**************************************************************************** + * Name: free + * + * Description: + * Returns a chunk of memory into the list of free nodes, merging with + * adjacent free chunks if possible. + * + ****************************************************************************/ + +void free(FAR void *mem) +{ + FAR struct mm_freenode_s *node; + FAR struct mm_freenode_s *prev; + FAR struct mm_freenode_s *next; + + mvdbg("Freeing %p\n", mem); + + /* Protect against attempts to free a NULL reference */ + + if (!mem) + { + return; + } + + /* We need to hold the MM semaphore while we muck with the + * nodelist. + */ + + mm_takesemaphore(); + + /* Map the memory chunk into a free node */ + + node = (FAR struct mm_freenode_s *)((char*)mem - SIZEOF_MM_ALLOCNODE); + node->preceding &= ~MM_ALLOC_BIT; + + /* Check if the following node is free and, if so, merge it */ + + next = (FAR struct mm_freenode_s *)((char*)node + node->size); + if ((next->preceding & MM_ALLOC_BIT) == 0) + { + FAR struct mm_allocnode_s *andbeyond; + + /* Get the node following the next node (which will + * become the new next node). We know that we can never + * index past the tail chunk because it is always allocated. + */ + + andbeyond = (FAR struct mm_allocnode_s*)((char*)next + next->size); + + /* 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; + } + + /* Then merge the two chunks */ + + node->size += next->size; + andbeyond->preceding = node->size | (andbeyond->preceding & MM_ALLOC_BIT); + next = (FAR struct mm_freenode_s *)andbeyond; + } + + /* Check if the preceding node is also free and, if so, merge + * it with this node + */ + + prev = (FAR struct mm_freenode_s *)((char*)node - node->preceding); + if ((prev->preceding & MM_ALLOC_BIT) == 0) + { + /* Remove the 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; + } + + /* Then merge the two chunks */ + + prev->size += node->size; + next->preceding = prev->size | (next->preceding & MM_ALLOC_BIT); + node = prev; + } + + /* Add the merged node to the nodelist */ + + mm_addfreechunk(node); + mm_givesemaphore(); +} |