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如何将 Linux 内核实现的红黑树 rbtree 运用到你的 C 程序中?

2012-09-02 23:48 Haippy 阅读(...) 评论(...) 编辑 收藏

相信大家都知道红黑树是什么吧,但是呢......如果你确实不知道,你不该穿越到这儿的,你应该去这里这里,还有这里看看,然后再来这里看看,最后如果大爷您赏脸,再来看看我吧 :-)

废话少说,直接入正题吧,Linux 内核为我们实现了简洁高效但是......却不那么容易使用的红黑树,如何在你的 C 程序里面使用内核开发者为我们实现的红黑树呢,别急别急,本文将一一为您呈现。

Linux 内核红黑树的实现代码位于:lib/rbtree.c,同时头文件在 include/linux/rbtree.h 中,内核中很多模块都使用了红黑树,详细介绍参见内核文档 Documentation/rbtree.txt。

内核中红黑树定义如下:

struct rb_node
{
    unsigned long  rb_parent_color;
#define    RB_RED        0
#define    RB_BLACK    1
    struct rb_node *rb_right;
    struct rb_node *rb_left;
} __attribute__((aligned(sizeof(long))));
struct rb_root
{
    struct rb_node *rb_node;
};

在使用内核的红黑树时,需将 struct rb_node 结构包含在自己的数据结构中,比如:

  struct mynode {
      struct rb_node node;
      char *string;
      /*more stuff of your structure hereby*/
  };

可以通过container_of宏获取包含了 rb_node 结构的起始地址,也可以通过rb_entry(node, type, member),其实:

 

#define    rb_entry(ptr, type, member) container_of(ptr, type, member)

 

container_of 中使用了offsetof宏,它们都是内核中常见的宏,其定义如下:

#if defined(container_of)
  #undef container_of
  #define container_of(ptr, type, member) ({            \
        const typeof( ((type *)0)->member ) *__mptr = (ptr);    \
        (type *)( (char *)__mptr - offsetof(type,member) );})
#endif

#if defined(offsetof)
  #undef offsetof
  #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
#endif

如果对上面两个宏的意思不理解,可以在本文后面留言 :-)

为了使用内核提供的红黑树,你需要自己实现插入和查找函数,如下:

struct mynode *my_search(struct rb_root *root, char *string)
{
      struct rb_node *node = root->rb_node;

      while (node) {
          struct mynode *data = container_of(node, struct mynode, node);
        int result;

        result = strcmp(string, data->string);

        if (result < 0)
              node = node->rb_left;
        else if (result > 0)
              node = node->rb_right;
        else
              return data;
    }
    return NULL;
}
int my_insert(struct rb_root *root, struct mynode *data) { struct rb_node **new = &(root->rb_node), *parent = NULL; /* Figure out where to put new node */ while (*new) { struct mynode *this = container_of(*new, struct mynode, node); int result = strcmp(data->string, this->string); parent = *new; if (result < 0) new = &((*new)->rb_left); else if (result > 0) new = &((*new)->rb_right); else return 0; } /* Add new node and rebalance tree. */ rb_link_node(&data->node, parent, new); rb_insert_color(&data->node, root); return 1; }

释放某一节点空间:

void my_free(struct mynode *node)
{
    if (node != NULL) {
        if (node->string != NULL) {
            free(node->string);
            node->string = NULL;
        }
        free(node);
        node = NULL;
    }
}

综合上面的代码:

#define NUM_NODES 32

int main()
{

    struct mynode *mn[NUM_NODES];

    /* *insert */
    int i = 0;
    for (; i < NUM_NODES; i++) {
        mn[i] = (struct mynode *)malloc(sizeof(struct mynode));
        mn[i]->string = (char *)malloc(sizeof(char) * 4);
        sprintf(mn[i]->string, "%d", i);
        my_insert(&mytree, mn[i]);
    }
    
    /* *search */
    struct rb_node *node;
    for (node = rb_first(&mytree); node; node = rb_next(node))
        printf("key = %s\n", rb_entry(node, struct mynode, node)->string);

    /* *delete */
    printf("delete node 20: \n");
    struct mynode *data = my_search(&mytree, "20");
    if (data) {
        rb_erase(&data->node, &mytree);
        my_free(data);
    }


    /* *delete again*/
    printf("delete node 10: \n");
    data = my_search(&mytree, "10");
    if (data) {
        rb_erase(&data->node, &mytree);
        my_free(data);
    }


    /* *delete once again*/
    printf("delete node 15: \n");
    data = my_search(&mytree, "15");
    if (data) {
        rb_erase(&data->node, &mytree);
        my_free(data);
    }

    /* *search again*/
    printf("search again:\n");
    for (node = rb_first(&mytree); node; node = rb_next(node))
        printf("key = %s\n", rb_entry(node, struct mynode, node)->string);
    return 0;
}

完整代码请移步我的githubhttps://github.com/forhappy/rbtree