redis lua原理分析-阿里云开发者社区

开发者社区> 阿里云数据库> 正文

redis lua原理分析

简介:

redis-2.6支持通过EVAL命令来执行lua脚本,对lua脚本的支持扩展了redis的应用场景,redis支持路脚本需要做2件事

  1. redis能执行lua脚本
  2. 在lua脚本里能执行redis的命令

接下来,我将通过一个简单的实例来解析redis如何完成上述两个工作的。

构建一个简单的redis

#define DICT_SIZE 100
struct redisDict {
  char* key[DICT_SIZE];
  char* value[DICT_SIZE];
  int  idx;
};

static void setCommand(const char *key, const char *value)
{
    /* ignore memory issue for simple */
    if (dict.idx + 1 <= DICT_SIZE) {
    dict.key[dict.idx] = (char *)malloc(strlen(key) + 1);
    strcpy(dict.key[dict.idx], key);

    dict.value[dict.idx] = (char *)malloc(strlen(value) + 1);
    strcpy(dict.value[dict.idx], value);

    dict.idx += 1;
  }
}

static const char *getCommand(const char *key)
{
  int j;
  for (j = 0; j <= dict.idx; j++) {
    if (strcmp(dict.key[j], key) == 0) {
      return dict.value[j];
    }
  }
  return "KeyNotFound";
}

上述代码实现了一个伪redis,支持setCommand、getCommand。

C调用lua脚本

具体例子参考http://lua-users.org/wiki/SimpleLuaApiExample

/*
 * All Lua contexts are held in this structure. We work with it almost
 * all the time.
 */
lua_State *L = luaL_newstate();

luaL_openlibs(L); /* Load Lua libraries */

/* Load the file containing the script we are going to run */
status = luaL_loadfile(L, "script.lua");

/* Ask Lua to run our little script */
result = lua_pcall(L, 0, LUA_MULTRET, 0);

上述代码片段中,其中script.lua是一个lua脚本。redis里稍有不同,redis里的脚本是通过EVAL命令传递到服务器端,redis将脚本拼成一个lua函数,然后调用loadbuffer,而这里从文件执行脚本调用的loadfile。

lua调用C函数

下面的lua代码里,调用的是redis的setCommand和getCommand。

redis.call("set", "foo", "bar");

return redis.call("get", "foo");

要想lua脚本能调用C代码,需要现在lua环境注册对应的C函数,参考redis的scriptingInit函数。

static int call(lua_State *L)
{
  int argc = lua_gettop(L);
  const char *cmd = lua_tostring(L, 1);
  const char *key = lua_tostring(L, 2);
  if (strcmp(cmd, "set") == 0) {
    assert(argc == 3);
    const char *value = lua_tostring(L, 3);
    setCommand(key, value);
   return 0;
  } else if (strcmp(cmd, "get") == 0) {
    assert(argc == 2);
    lua_pushstring(L, getCommand(key));
    return 1;
  }

  lua_pushstring(L, "Invalid Command");
  return 1;
}

static void scriptingInit()
{

  L = luaL_newstate();

  luaL_openlibs(L);

  /* Register the redis commands table and fields */
  lua_newtable(L);

  /* redis.call */
  lua_pushstring(L, "call");
  lua_pushcfunction(L, call);
  lua_settable(L, -3);

  /* Finally set the table as 'redis' global var. */
  lua_setglobal(L, "redis");
}

完整示例代码

 1
 2

redis.call("set", "foo", "bar");
return redis.call("get", "foo");
 来自CODE的代码片
script.lua

   1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116

/* gcc -o test_lua lua.c -llua -lm -ldl */
#include <lua.h>
#include <lauxlib.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>

#define DICT_SIZE 100
struct redisDict {
char* key[DICT_SIZE];
char* value[DICT_SIZE];
int idx;
};

struct redisDict dict;
lua_State *L;

static void setCommand(const char *key, const char *value)
{
/* ignore memory issue for simple */
if (dict.idx + 1 <= DICT_SIZE) {
dict.key[dict.idx] = (char *)malloc(strlen(key) + 1);
strcpy(dict.key[dict.idx], key);

dict.value[dict.idx] = (char *)malloc(strlen(value) + 1);
strcpy(dict.value[dict.idx], value);

dict.idx += 1;
}
}

static const char *getCommand(const char *key)
{
int j;
for (j = 0; j <= dict.idx; j++) {
if (strcmp(dict.key[j], key) == 0) {
return dict.value[j];
}
}
return "KeyNotFound";
}

static int call(lua_State *L)
{
int argc = lua_gettop(L);
const char *cmd = lua_tostring(L, 1);
const char *key = lua_tostring(L, 2);
if (strcmp(cmd, "set") == 0) {
assert(argc == 3);
const char *value = lua_tostring(L, 3);
setCommand(key, value);
return 0;
} else if (strcmp(cmd, "get") == 0) {
assert(argc == 2);
lua_pushstring(L, getCommand(key));
return 1;
}

lua_pushstring(L, "Invalid Command");
return 1;
}

static void scriptingRun(const char* filename)
{
int status = luaL_loadfile(L, filename);
if (status) {
fprintf(stderr, "Couldn't load file: %s\n", lua_tostring(L, -1));
exit(1);
}

/* Ask Lua to run our little script */
int result = lua_pcall(L, 0, LUA_MULTRET, 0);
if (result) {
fprintf(stderr, "Failed to run script: %s\n", lua_tostring(L, -1));
exit(1);
}

/* Get the returned value at the top of the stack (index -1) */
const char *value = lua_tostring(L, -1);

printf("%s\n", value);

lua_pop(L, 1); /* Take the returned value out of the stack */
lua_close(L); /* Cya, Lua */
}

static void scriptingInit()
{
/*
* All Lua contexts are held in this structure. We work with it almost
* all the time.
*/
L = luaL_newstate();

/* Load Lua libraries */
luaL_openlibs(L);

/* Register the redis commands table and fields */
lua_newtable(L);

/* redis.call */
lua_pushstring(L, "call");
lua_pushcfunction(L, call);
lua_settable(L, -3);

/* Finally set the table as 'redis' global var. */
lua_setglobal(L, "redis");
}

int main(void)
{
scriptingInit();
scriptingRun("script.lua");
return 0;
}
 来自CODE的代码片
lua.c

版权声明:本文内容由阿里云实名注册用户自发贡献,版权归原作者所有,阿里云开发者社区不拥有其著作权,亦不承担相应法律责任。具体规则请查看《阿里云开发者社区用户服务协议》和《阿里云开发者社区知识产权保护指引》。如果您发现本社区中有涉嫌抄袭的内容,填写侵权投诉表单进行举报,一经查实,本社区将立刻删除涉嫌侵权内容。

分享:
阿里云数据库
使用钉钉扫一扫加入圈子
+ 订阅

帮用户承担一切数据库风险,给您何止是安心!

官方博客
链接