freelist.c

Upnp开发包文件

///////////////////////////////////////////////////////////////////////////
//
// Copyright (c) 2000-2003 Intel Corporation 
// All rights reserved. 
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// modification, are permitted provided that the following conditions are met: 
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// this list of conditions and the following disclaimer. 
// * Redistributions in binary form must reproduce the above copyright notice, 
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// may be used to endorse or promote products derived from this software 
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///////////////////////////////////////////////////////////////////////////

#include "FreeList.h"

#include <assert.h>

/****************************************************************************
 * Function: FreeListInit
 *
 *  Description:
 *      Initializes Free List. Must be called first.
 *      And only once for FreeList.
 *  Parameters:
 *      free_list  - must be valid, non null, pointer to a linked list.
 *      size_t -     size of elements to store in free list
 *      maxFreeListSize - max size that the free list can grow to
 *                        before returning memory to O.S.
 *  Returns:
 *      0 on success. Nonzero on failure.
 *      Always returns 0.
 *****************************************************************************/
int
FreeListInit( FreeList * free_list,
              size_t elementSize,
              int maxFreeListLength )
{
    assert( free_list != NULL );

    if( free_list == NULL )
        return EINVAL;

    free_list->element_size = elementSize;
    free_list->maxFreeListLength = maxFreeListLength;
    free_list->head = NULL;
    free_list->freeListLength = 0;
    return 0;
}

/****************************************************************************
 * Function: FreeListAlloc
 *
 *  Description:
 *      Allocates chunk of set size.
 *      If a free item is available in the list, returnes the stored item.
 *      Otherwise calls the O.S. to allocate memory.
 *  Parameters:
 *      free_list  - must be valid, non null, pointer to a linked list.
 *  Returns:
 *      Non NULL on success. NULL on failure.
 *****************************************************************************/
void *
FreeListAlloc( FreeList * free_list )
{
    FreeListNode *ret = NULL;

    assert( free_list != NULL );

    if( free_list == NULL )
        return NULL;

    if( free_list->head ) {
        ret = free_list->head;
        free_list->head = free_list->head->next;
        free_list->freeListLength--;
    } else {
        ret = malloc( free_list->element_size );
    }

    return ret;
}

/****************************************************************************
 * Function: FreeListFree
 *
 *  Description:
 *      Returns an item to the Free List.
 *      If the free list is smaller than the max size than
 *      adds the item to the free list.
 *      Otherwise returns the item to the O.S.
 *  Parameters:
 *      free_list  - must be valid, non null, pointer to a free list.
 *      element - must be a pointer allocated by FreeListAlloc
 *  Returns:
 *      0 on success. Nonzero on failure.
 *      Always returns 0.
 *****************************************************************************/
int
FreeListFree( FreeList * free_list,
              void *element )
{

    FreeListNode *temp = NULL;

    assert( free_list != NULL );

    if( free_list == NULL )
        return EINVAL;

    if( ( element != NULL ) &&
        ( ( free_list->freeListLength + 1 ) <
          free_list->maxFreeListLength ) ) {
        free_list->freeListLength++;
        temp = ( FreeListNode * ) element;
        temp->next = free_list->head;
        free_list->head = temp;

    } else {

        free( element );
    }

    return 0;
}

/****************************************************************************
 * Function: FreeListDestroy
 *
 *  Description:
 *      Releases the resources stored with the free list.
 *  Parameters:
 *      free_list  - must be valid, non null, pointer to a linked list.
 *  Returns:
 *      0 on success. Nonzero on failure.
 *      Always returns 0.
 *****************************************************************************/
int
FreeListDestroy( FreeList * free_list )
{
    FreeListNode *temp = NULL;
    int i = 0;

    assert( free_list != NULL );

    if( free_list == NULL )
        return EINVAL;

    while( free_list->head ) {
        i++;
        temp = free_list->head->next;
        free( free_list->head );
        free_list->head = temp;
    }

    free_list->freeListLength = 0;

    return 0;
}