void mm_free()

in RISC-V_RV32_THEAD_SMART_CDS/libs/mm/mm_free.c [70:177]

• 58 lines of code
• 8 McCabe index (conditional complexity)

void mm_free(struct mm_heap_s *heap, void *mem, void *caller)
{
  struct mm_freenode_s *node;
  struct mm_freenode_s *prev;
  struct mm_freenode_s *next;

  (void)caller;
  //mvdbg("Freeing %p\n", mem);

  /* Protect against attempts to free a NULL reference */

  if (!mem)
    {
      return;
    }

#if defined(CONFIG_MM_DETECT_ERROR)
  struct m_dbg_hdr *hdr = (struct m_dbg_hdr *)((uint8_t *)mem - MDBG_SZ_HEAD);
  if (!mdbg_check_magic_hdr(hdr)) {
    printf("mm magic hdr err %p,%p\n", hdr->caller, caller);
    mm_leak_search_chunk(hdr);
    /* force trapping */
    *(volatile void **)0 = 0;
  }
  if (!mdbg_check_magic_end(hdr)) {
    printf("mm magic end err %p,%p", hdr->caller, caller);
    mm_leak_search_chunk(hdr+1);
    /* force trapping */
    *(volatile void **)0 = 0;
  }
  mem = hdr;
  hdr->magic = MAGIC_FREE;
  mm_leak_del_chunk(hdr);
#endif

  /* We need to hold the MM semaphore while we muck with the
   * nodelist.
   */

  mm_takesemaphore(heap);

  /* Map the memory chunk into a free node */

  node = (struct mm_freenode_s *)((uint32_t)mem - SIZEOF_MM_ALLOCNODE);
  node->preceding &= ~MM_ALLOC_BIT;

  /* Check if the following node is free and, if so, merge it */

  next = (struct mm_freenode_s *)((uint32_t)node + node->size);
  if ((next->preceding & MM_ALLOC_BIT) == 0)
    {
      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 = (struct mm_allocnode_s *)((uint32_t)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                 = (struct mm_freenode_s *)andbeyond;
    }

  /* Check if the preceding node is also free and, if so, merge
   * it with this node
   */

  prev = (struct mm_freenode_s *)((uint32_t)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(heap, node);
  mm_givesemaphore(heap);
}