LwIP之動態內存堆

下面這段宏定義了內存堆

#ifndef LWIP_RAM_HEAP_POINTER
LWIP_DECLARE_MEMORY_ALIGNED(ram_heap, MEM_SIZE_ALIGNED + (2U * SIZEOF_STRUCT_MEM));
#define LWIP_RAM_HEAP_POINTER ram_heap    //內存堆指針
#endif

將宏LWIP_DECLARE_MEMORY_ALIGNED展開，發現內存堆就是一個數組。

#ifndef LWIP_DECLARE_MEMORY_ALIGNED
#define LWIP_DECLARE_MEMORY_ALIGNED(variable_name, size) u8_t variable_name[LWIP_MEM_ALIGN_BUFFER(size)]
#endif

動態堆最後被組織成內存塊分配給程序，或者從程序釋放到內存堆。

所謂的管理就是管理這些內存塊，下面是對內存塊的定義。而這些內存塊最終會被掛接到一條鏈表。

/* 內存塊結構體 */
struct mem {
  /* 指向後一個內存塊 */
  mem_size_t next;
  /* 指向前一個內存塊 */
  mem_size_t prev;
  /* 內存塊是否被使用 1:被使用 0:未使用 */
  u8_t used;
 
#if MEM_OVERFLOW_CHECK
  mem_size_t user_size;
#endif
};

 

初始化堆內存，將對內部組織成內存塊鏈表。

/* 初始化堆內存 */
void mem_init(void)
{
  struct mem *mem;

  LWIP_ASSERT("Sanity check alignment", (SIZEOF_STRUCT_MEM & (MEM_ALIGNMENT - 1)) == 0);

  /* 內存堆對齊 */
  ram = (u8_t *)LWIP_MEM_ALIGN(LWIP_RAM_HEAP_POINTER);

  /* 在內存堆起始處組織一個內存塊 */
  mem = (struct mem *)(void *)ram;
  /* 下一個內存塊指向內存堆結尾 */
  mem->next = MEM_SIZE_ALIGNED;
  /* 上一個內存塊爲空 */
  mem->prev = 0;
  /* 該內存塊未使用 */
  mem->used = 0;
  
  /* 在內存堆結尾處組織一個內存塊 */
  ram_end = ptr_to_mem(MEM_SIZE_ALIGNED);
  /* 該內存塊已使用 */
  ram_end->used = 1;
  /* 上一個內存塊指向自身 */
  ram_end->next = MEM_SIZE_ALIGNED;
  /* 下一個內存塊指向自身 */
  ram_end->prev = MEM_SIZE_ALIGNED;
  
  MEM_SANITY();

  /* 內存堆起始處初始化爲地址最低的空閒塊 */
  lfree = (struct mem *)(void *)ram;

  MEM_STATS_AVAIL(avail, MEM_SIZE_ALIGNED);

  /* 創建一個互斥鎖 */
  if (sys_mutex_new(&mem_mutex) != ERR_OK) {
    LWIP_ASSERT("failed to create mem_mutex", 0);
  }
}

 

內存分配，從鏈表中找到一個合適的內存塊，分配給程序。將剩下的內存組織成新的內存塊，並掛接到鏈表。

/* 申請內存 */
void *mem_malloc(mem_size_t size_in)
{
  mem_size_t ptr, ptr2, size;
  struct mem *mem, *mem2;
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
  u8_t local_mem_free_count = 0;
#endif
  LWIP_MEM_ALLOC_DECL_PROTECT();

  if (size_in == 0) {
    return NULL;
  }

  /* 字節數對齊 */
  size = (mem_size_t)LWIP_MEM_ALIGN_SIZE(size_in);
  /* 內存最小12字節 */
  if (size < MIN_SIZE_ALIGNED) {
    size = MIN_SIZE_ALIGNED;
  }
#if MEM_OVERFLOW_CHECK
  size += MEM_SANITY_REGION_BEFORE_ALIGNED + MEM_SANITY_REGION_AFTER_ALIGNED;
#endif
  if ((size > MEM_SIZE_ALIGNED) || (size < size_in)) {
    return NULL;
  }

  /* 獲取互斥鎖 */
  sys_mutex_lock(&mem_mutex);
  
  LWIP_MEM_ALLOC_PROTECT();
  
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
  do {
    local_mem_free_count = 0;
#endif

    /* 遍歷所有內存塊 */
    for (ptr = mem_to_ptr(lfree); ptr < MEM_SIZE_ALIGNED - size; ptr = ptr_to_mem(ptr)->next) 
    {
      /* 內存塊地址 */
      mem = ptr_to_mem(ptr);

#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
      mem_free_count = 0;
      LWIP_MEM_ALLOC_UNPROTECT();
 
      LWIP_MEM_ALLOC_PROTECT();
      if (mem_free_count != 0) 
      {
        local_mem_free_count = 1;
        break;
      }
#endif

		/* 內存塊未使用，且滿足分配大小(請求大小+內存塊結構體大小) */
       if ((!mem->used) && (mem->next - (ptr + SIZEOF_STRUCT_MEM)) >= size) 
       {
        /* 內存塊過大(剩餘內存還夠分配最小內存塊) */
        if (mem->next - (ptr + SIZEOF_STRUCT_MEM) >= (size + SIZEOF_STRUCT_MEM + MIN_SIZE_ALIGNED)) 
        {
          /* 剩下的內存地址 */
          ptr2 = (mem_size_t)(ptr + SIZEOF_STRUCT_MEM + size);
          LWIP_ASSERT("invalid next ptr",ptr2 != MEM_SIZE_ALIGNED);
          /* 將剩下的內存地址轉換爲內存塊結構體指針 */
          mem2 = ptr_to_mem(ptr2);
          /* 新的內存塊未使用 */
          mem2->used = 0;
          /* 將新的內存塊插入鏈表 */
          mem2->next = mem->next;
          mem2->prev = ptr;
          mem->next = ptr2;

          /* 該內存塊設置爲已使用 */
          mem->used = 1;

          /* 如果不是最後一個內存塊，則下一個內存塊指向新內存塊 */
          if (mem2->next != MEM_SIZE_ALIGNED) {
            ptr_to_mem(mem2->next)->prev = ptr2;
          }

          MEM_STATS_INC_USED(used, (size + SIZEOF_STRUCT_MEM));
        }
        /* 如果剩餘內存不夠重新組織一個新內存塊 */
        else
        {
          /* 該內存塊已使用 */
          mem->used = 1;
          MEM_STATS_INC_USED(used, mem->next - mem_to_ptr(mem));
        }

#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
mem_malloc_adjust_lfree:
#endif

		/* 如果該內存塊爲地址最低的空閒塊，則要更新地址最低空閒塊 */
        if (mem == lfree) 
        {
          struct mem *cur = lfree;

          /* 遍歷向後的所有內存塊，找出地址最低的空閒塊 */
          while (cur->used && cur != ram_end) 
          {
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
            mem_free_count = 0;
            LWIP_MEM_ALLOC_UNPROTECT();
            LWIP_MEM_ALLOC_PROTECT();
            if (mem_free_count != 0) {
              goto mem_malloc_adjust_lfree;
            }
#endif
            cur = ptr_to_mem(cur->next);
          }

          /* 更新地址最低的空閒塊 */
          lfree = cur;

          LWIP_ASSERT("mem_malloc: !lfree->used", ((lfree == ram_end) || (!lfree->used)));
        }
        
        LWIP_MEM_ALLOC_UNPROTECT();

		/* 釋放互斥鎖 */
        sys_mutex_unlock(&mem_mutex);
        
        LWIP_ASSERT("mem_malloc: allocated memory not above ram_end.",
                    (mem_ptr_t)mem + SIZEOF_STRUCT_MEM + size <= (mem_ptr_t)ram_end);
        LWIP_ASSERT("mem_malloc: allocated memory properly aligned.",
                    ((mem_ptr_t)mem + SIZEOF_STRUCT_MEM) % MEM_ALIGNMENT == 0);
        LWIP_ASSERT("mem_malloc: sanity check alignment",
                    (((mem_ptr_t)mem) & (MEM_ALIGNMENT - 1)) == 0);

#if MEM_OVERFLOW_CHECK
        mem_overflow_init_element(mem, size_in);
#endif

        MEM_SANITY();

		/* 返回內存地址 */
        return (u8_t *)mem + SIZEOF_STRUCT_MEM + MEM_SANITY_OFFSET;
      }
    }
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
  } 
  while (local_mem_free_count != 0);
#endif
  MEM_STATS_INC(err);
  
  LWIP_MEM_ALLOC_UNPROTECT();
  
  sys_mutex_unlock(&mem_mutex);
  
  LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("mem_malloc: could not allocate %"S16_F" bytes\n", (s16_t)size));

  return NULL;
}

 

釋放內存，將內存重新組織成內存塊插入鏈表。相鄰內存堆都空閒，需要合併。

/* 釋放內存 */
void mem_free(void *rmem)
{
  struct mem *mem;

  LWIP_MEM_FREE_DECL_PROTECT();

  /* 參數合法性驗證，釋放的指針不能爲空 */
  if (rmem == NULL) 
  {
    LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("mem_free(p == NULL) was called.\n"));
    return;
  }

  /* 參數合法性驗證，釋放的指針必須要字節對齊 */
  if ((((mem_ptr_t)rmem) & (MEM_ALIGNMENT - 1)) != 0) 
  {
    LWIP_MEM_ILLEGAL_FREE("mem_free: sanity check alignment");
    LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_LEVEL_SEVERE, ("mem_free: sanity check alignment\n"));
    MEM_STATS_INC_LOCKED(illegal);
    return;
  }

  /* 內存指針向前偏移一個內存塊結構體大小 */
  mem = (struct mem *)(void *)((u8_t *)rmem - (SIZEOF_STRUCT_MEM + MEM_SANITY_OFFSET));

  /* 參數合法性驗證，釋放的指針必須在內存堆中 */
  if ((u8_t *)mem < ram || (u8_t *)rmem + MIN_SIZE_ALIGNED > (u8_t *)ram_end)
  {
    LWIP_MEM_ILLEGAL_FREE("mem_free: illegal memory");
    LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_LEVEL_SEVERE, ("mem_free: illegal memory\n"));
    MEM_STATS_INC_LOCKED(illegal);
    return;
  }
#if MEM_OVERFLOW_CHECK
  mem_overflow_check_element(mem);
#endif

  LWIP_MEM_FREE_PROTECT();

  /* 參數合法性驗證，內存塊必須已經分配 */
  if (!mem->used) 
  {
    LWIP_MEM_ILLEGAL_FREE("mem_free: illegal memory: double free");
    LWIP_MEM_FREE_UNPROTECT();
    LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_LEVEL_SEVERE, ("mem_free: illegal memory: double free?\n"));
    MEM_STATS_INC_LOCKED(illegal);
    return;
  }

  /* 參數合法性驗證，檢查內存塊是否鏈接在鏈表中 */
  if (!mem_link_valid(mem)) 
  {
    LWIP_MEM_ILLEGAL_FREE("mem_free: illegal memory: non-linked: double free");
    LWIP_MEM_FREE_UNPROTECT();
    LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_LEVEL_SEVERE, ("mem_free: illegal memory: non-linked: double free?\n"));
    MEM_STATS_INC_LOCKED(illegal);
    return;
  }

  /* 將內存塊設置爲未使用 */
  mem->used = 0;

  /* 內存塊地址小於最低地址空閒塊 */
  if (mem < lfree) 
  {
    /* 更新最低地址空閒塊 */
    lfree = mem;
  }

  MEM_STATS_DEC_USED(used, mem->next - (mem_size_t)(((u8_t *)mem - ram)));

  /* 合併空閒塊 */
  plug_holes(mem);
  
  MEM_SANITY();
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
  mem_free_count = 1;
#endif

  LWIP_MEM_FREE_UNPROTECT();
}

/* 合併空閒塊 */
static void plug_holes(struct mem *mem)
{
  struct mem *nmem;
  struct mem *pmem;

  LWIP_ASSERT("plug_holes: mem >= ram", (u8_t *)mem >= ram);
  LWIP_ASSERT("plug_holes: mem < ram_end", (u8_t *)mem < (u8_t *)ram_end);
  LWIP_ASSERT("plug_holes: mem->used == 0", mem->used == 0);

  LWIP_ASSERT("plug_holes: mem->next <= MEM_SIZE_ALIGNED", mem->next <= MEM_SIZE_ALIGNED);

  /* 下一個內存塊 */
  nmem = ptr_to_mem(mem->next);

  /* 下一個內存塊未被使用，並且不是最後一個內存塊 */
  if (mem != nmem && nmem->used == 0 && (u8_t *)nmem != (u8_t *)ram_end)
  {
    /* 下一個空閒塊是最小地址空閒塊 */
    if (lfree == nmem) 
    {
      /* 更新最小地址空閒塊 */
      lfree = mem;
    }

    /* 合併後一個內存塊 */
    mem->next = nmem->next;
    if (nmem->next != MEM_SIZE_ALIGNED)
    {
      ptr_to_mem(nmem->next)->prev = mem_to_ptr(mem);
    }
  }

  /* 上一個內存塊 */
  pmem = ptr_to_mem(mem->prev);

  /* 上一個內存塊未使用 */
  if (pmem != mem && pmem->used == 0) 
  {
    /* 該內存塊是最小地址空閒塊 */
    if (lfree == mem) 
    {
      /* 更新最小地址空閒塊 */
      lfree = pmem;
    }

    /* 合併上一個內存塊 */
    pmem->next = mem->next;
    if (mem->next != MEM_SIZE_ALIGNED) 
    {
      ptr_to_mem(mem->next)->prev = mem_to_ptr(pmem);
    }
  }
}

 

除了基本的分配和釋放，協議棧還mem_trim函數和mem_calloc函數

mem_trim函數，能夠收縮內存，將原有的內存縮小。縮小的部分重新組織成內存塊，掛接到鏈表。

/* 收縮內存 */
void *mem_trim(void *rmem, mem_size_t new_size)
{
  mem_size_t size, newsize;
  mem_size_t ptr, ptr2;
  struct mem *mem, *mem2;

  LWIP_MEM_FREE_DECL_PROTECT();

  /* 新的內存大小字節對齊 */
  newsize = (mem_size_t)LWIP_MEM_ALIGN_SIZE(new_size);
  /* 字節大小大於最小內存字節 */
  if (newsize < MIN_SIZE_ALIGNED) 
  {
    newsize = MIN_SIZE_ALIGNED;
  }

#if MEM_OVERFLOW_CHECK
  newsize += MEM_SANITY_REGION_BEFORE_ALIGNED + MEM_SANITY_REGION_AFTER_ALIGNED;
#endif

  /* 參數合法性驗證，新的內存大小不能大於內存堆 */
  if ((newsize > MEM_SIZE_ALIGNED) || (newsize < new_size)) {
    return NULL;
  }

  LWIP_ASSERT("mem_trim: legal memory", (u8_t *)rmem >= (u8_t *)ram && (u8_t *)rmem < (u8_t *)ram_end);

  /* 參數合法性驗證，內存必須在內存堆中 */
  if ((u8_t *)rmem < (u8_t *)ram || (u8_t *)rmem >= (u8_t *)ram_end)
  {
    LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_LEVEL_SEVERE, ("mem_trim: illegal memory\n"));
    MEM_STATS_INC_LOCKED(illegal);
    return rmem;
  }
  
  /* 內存指針向前偏移內存塊結構體大小 */
  mem = (struct mem *)(void *)((u8_t *)rmem - (SIZEOF_STRUCT_MEM + MEM_SANITY_OFFSET));
#if MEM_OVERFLOW_CHECK
  mem_overflow_check_element(mem);
#endif

  /* 內存指針轉偏移量 */
  ptr = mem_to_ptr(mem);

  /* 當前內存塊，內存大小 */
  size = (mem_size_t)((mem_size_t)(mem->next - ptr) - (SIZEOF_STRUCT_MEM + MEM_SANITY_OVERHEAD));
  LWIP_ASSERT("mem_trim can only shrink memory", newsize <= size);

  /* 參數合法性驗證，新內存大小不能大於原內存大小 */
  if (newsize > size) 
  {
    return NULL;
  }

  /* 新內存大小如果等於原內存大小，什麼也不用做 */
  if (newsize == size) 
  {
    return rmem;
  }

  LWIP_MEM_FREE_PROTECT();

  /* 下一個內存塊指針 */
  mem2 = ptr_to_mem(mem->next);
  /* 下一個內存塊未使用，需要合併 */
  if (mem2->used == 0) 
  {
    mem_size_t next;
    LWIP_ASSERT("invalid next ptr", mem->next != MEM_SIZE_ALIGNED);

    /* 下下個內存偏移量 */
    next = mem2->next;
    /* 截取之後，剩餘內存塊指針 */
    ptr2 = (mem_size_t)(ptr + SIZEOF_STRUCT_MEM + newsize);
	/* 下一個內存塊是地址最低空閒塊 */
    if (lfree == mem2) 
    {
      /* 更新最低空閒塊指針 */
      lfree = ptr_to_mem(ptr2);
    }
    /* 剩餘內存塊指針 */
    mem2 = ptr_to_mem(ptr2);
    /* 剩餘內存塊設置爲未使用 */
    mem2->used = 0;
    
    /* 將剩餘空閒塊和下一個內存塊合併插入鏈表 */
    mem2->next = next;
    mem2->prev = ptr;
    mem->next = ptr2;

    /* 不是最後一個內存塊，要讓下一個內存塊指向自己 */
    if (mem2->next != MEM_SIZE_ALIGNED) 
    {
      ptr_to_mem(mem2->next)->prev = ptr2;
    }
    MEM_STATS_DEC_USED(used, (size - newsize));
  }
  /* 下一個內存塊不空閒，並且剩餘的內存還夠組織新的內存塊 */
  else if (newsize + SIZEOF_STRUCT_MEM + MIN_SIZE_ALIGNED <= size) 
  {
    /* 剩餘的內存塊指針 */
    ptr2 = (mem_size_t)(ptr + SIZEOF_STRUCT_MEM + newsize);

    LWIP_ASSERT("invalid next ptr", mem->next != MEM_SIZE_ALIGNED);

    /* 內存塊轉換爲偏移量 */
    mem2 = ptr_to_mem(ptr2);

    /* 剩餘內存塊地址小於最小地址空閒塊 */
    if (mem2 < lfree) 
    {
      /* 更新最小地址空閒塊 */
      lfree = mem2;
    }
    /* 剩餘內存塊未使用 */
    mem2->used = 0;
    
    /* 將剩餘內存塊插入鏈表 */
    mem2->next = mem->next;
    mem2->prev = ptr;
    mem->next = ptr2;
    if (mem2->next != MEM_SIZE_ALIGNED)
    {
      ptr_to_mem(mem2->next)->prev = ptr2;
    }
    MEM_STATS_DEC_USED(used, (size - newsize));
  }
  
#if MEM_OVERFLOW_CHECK
  mem_overflow_init_element(mem, new_size);
#endif

  MEM_SANITY();
  
#if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
  mem_free_count = 1;
#endif

  LWIP_MEM_FREE_UNPROTECT();
  
  return rmem;
}

mem_calloc函數，申請內存的同時，將內存清空。

/* 申請並清空內存 */
void *mem_calloc(mem_size_t count, mem_size_t size)
{
  void *p;
  size_t alloc_size = (size_t)count * (size_t)size;

  if ((size_t)(mem_size_t)alloc_size != alloc_size) 
  {
    LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("mem_calloc: could not allocate %"SZT_F" bytes\n", alloc_size));
    return NULL;
  }

  /* 申請內存 */
  p = mem_malloc((mem_size_t)alloc_size);
  /* 申請成功 */
  if (p) 
  {
    /* 清空內存 */
    memset(p, 0, alloc_size);
  }
  return p;
}