libmemcached一致性hash算法详解(2)----简化版的libmemcached一致性hash算法实现

author: selfimpr

blog: http://blog.csdn.net/lgg201

mail: [email protected]

上一篇文档见

libmemcached一致性hash算法详解(1)----php-memcached客户端一致性哈希与crc算法共用产生的bug分析

这里就不废话了, 直接上代码:

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>

/*---------------------------以下部分摘自libmemcached/crc.c--------------------------*/
static const uint32_t crc32tab[256] = {
  0x00000000, 0x77073096, 0xee0e612c, 0x990951ba,
  0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3,
  0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
  0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91,
  0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
  0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
  0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,
  0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5,
  0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
  0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
  0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940,
  0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
  0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116,
  0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,
  0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
  0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,
  0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a,
  0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
  0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818,
  0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
  0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
  0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457,
  0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c,
  0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
  0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
  0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb,
  0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
  0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,
  0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086,
  0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
  0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4,
  0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad,
  0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
  0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683,
  0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
  0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
  0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe,
  0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7,
  0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
  0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
  0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252,
  0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
  0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60,
  0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79,
  0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
  0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f,
  0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04,
  0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
  0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a,
  0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
  0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
  0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21,
  0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e,
  0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
  0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
  0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,
  0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
  0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db,
  0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0,
  0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
  0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6,
  0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf,
  0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
  0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d,
};

uint32_t hash_crc32(const char *key, size_t key_length)
{
  uint32_t x;
  uint32_t crc= UINT32_MAX;

  for (x= 0; x < key_length; x++)
    crc= (crc >> 8) ^ crc32tab[(crc ^ (key[x])) & 0xff];

  return ~crc;
}
/*---------------------------以上部分摘自libmemcached/crc.c--------------------------*/

//libmemcached中使用crc求hash值的方法
uint32_t memcached_hash_crc32(const char *key, size_t key_len) {
	return ((hash_crc32(key, key_len) >> 16) & 0x7fff);
}

/**
 * 模拟libmemcached的一致性hash算法中的点  
 * libmemcached中, 假设有A,B两台服务器, 则其一致性算法为:
 * 	1. 假设每台服务器100个点
 * 	2. 每个点是一个类似下面的server_t的结构, 一个字段存放server的索引, 一个字段存放值
 * 	3. 每个服务器构造自己对应的100个点时, 对host:port-i求hash值, 其中host为服务器地址, port为端口, i为0-99的数
 * 	4. 将两个服务器总共产生的200个点放入一个数组, 按照点的value(即上面求得的hash值)排序
 * 下面是拿到一个key进行分布时的策略
 * 	1. 对key求一个hash值
 * 	2. 从上面得到的服务器的200个点的数组中, 二分查找离这个key产生的hash值最近的点
 * 	3. 拿到这个点对应的服务器
 */
typedef struct _server {
	char host[128];
	uint32_t value;
} server_t;

//libmemcached中点的比较函数
int server_cmp(const void *s1, const void *s2) {
	server_t *cs1 = (server_t *)s1;
	server_t *cs2 = (server_t *)s2;
	if ( cs1->value == cs2->value ) return 0;
	else if ( cs1->value > cs2->value ) return 1;
	else return -1;
}

//打印从servers开始的n个点
void print_servers(const server_t *servers, int n) {
	int i = 0;
	while ( i < n) {
		printf("server: %s, value: %d\n", (servers + i)->host, (servers + i)->value);
		i ++;
	}
}
//构造示例性的2台服务器产生的点, libmemcached中的算法简化了就是如此
server_t *construct_servers() {
	server_t *servers = malloc(sizeof(server_t) * 200);
	int i = 0, j;
	int server_length = 0;
	char server[128];
	while ( i < 2 ) {
		for ( j = 0; j < 100; j ++ ) {
			server_length = sprintf(server, "127.0.0.1:%d-%d", i ? 11211 : 11212, j);
			strcpy((servers + i * 100 + j)->host, server);
			(servers + i * 100 + j)->value = memcached_hash_crc32(server, server_length);
		}
		i ++;
	}
	qsort(servers, 200, sizeof(server_t), server_cmp);
	//print_servers(servers, 200);
	return servers;
}
//给定一个key, 查找对应的服务器, libmemcached的查找算法简化板
void search(server_t *servers, int num, char *key, int key_len) {
	server_t *begin, *left, *middle, *right, *end;	
	begin = left = servers;
	end = right = servers + num;
	uint32_t hash;
	hash = memcached_hash_crc32(key, key_len);

	while (left < right) {
		middle= left + (right - left) / 2;
		if (middle->value < hash) left= middle + 1;
		else right= middle;
	}
	if (right == end) right= begin;
	printf("key: %s, server: %s\n", key, right->host);
}

//下面是模拟的一个分布测试程序
void main(void) {
	server_t *servers;
	uint32_t hash;
	char key[128];
	int i = 0, key_len;

	servers = construct_servers();

	while ( i < 100 ) {
		key_len = sprintf(key, "item-%d", i ++);
		search(servers, 200, key, key_len);
	}
}