1. lua_shared_dict 指令介绍

原文： lua_shared_dict

syntax：lua_shared_dict <name> <size>

default: no

context: http

phase: depends on usage

声明一个共享内存区域 name，以充当基于 Lua 字典 ngx.shared.<name> 的共享存储。

共享内存总是被当前 Nginx 服务器实例中所有的 Nginx worker 进程所共享。

size 参数接受大小单位，如 k，m：

http {

    lua_shared_dict dogs 10m;

    ...

}

详细参见： ngx.shared.DICT

2. 源码分析

lua_shared_dict 指令位于 ngx_http_lua_module.c 文件中：

static ngx_command_t ngx_http_lua_cmds[] = {

    ...

    { ngx_string("lua_shared_dict"),

      NGX_HTTP_MAIN_CONF|NGX_CONF_TAKE2,

      ngx_http_lua_shared_dict,

      0,

      0,

      NULL },

    ...

}

2.1 ngx_http_lua_shared_dict

char *

ngx_http_lua_shared_dict(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)

{

    ngx_http_lua_main_conf_t   *lmcf = conf;

    ngx_str_t                  *value, name;

    ngx_shm_zone_t             *zone;

    ngx_shm_zone_t            **zp;

    ngx_http_lua_shdict_ctx_t  *ctx;

    ssize_t                     size;

    if (lmcf->shdict_zones == NULL) {

        lmcf->shdict_zones = ngx_palloc(cf->pool, sizeof(ngx_array_t));

        if (lmcf->shdict_zones == NULL) {

            return NGX_CONF_ERROR;

        }

        if (ngx_array_init(lmcf->shdict_zones, cf->pool, 2,

                           sizeof(ngx_shm_zone_t *))

            != NGX_OK)

        {

            return NGX_CONF_ERROR;

        }

    }

    value = cf->args->elts;

    ctx = NULL;

    if (value[1].len == 0) {

        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,

                           "invalid lua shared dict name \"%V"\"", &value[1]);

        return NGX_CONF_ERROR;

    }

    /* 共享内存的名称 */

    name = value[1];

    /* 解析需要分配的共享内存大小 */

    size = ngx_parse_size(&value[2]);

    if (size <= 8191) {

        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,

                           "invalid lua shared dict size \"%V\"", &value[2]);

        return NGX_CONF_ERROR;

    }

    ctx = ngx_pcalloc(cf->pool, sizeof(ngx_http_lua_shdict_ctx_t));

    if (ctx == NULL) {

        return NGX_CONF_ERROR;

    }

    ctx->name = name;

    ctx->main_conf = lmcf;

    ctx->log = &cf->cycle->new_log;

    zone = ngx_http_lua_shared_memory_add(cf, &name, (size_t) size,

                                          &ngx_http_lua_module);

    if (zone == NULL) {

        return NGX_CONF_ERROR;

    }

    if (zone->data) {

        ctx = zone->data;

        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,

                           "lua_shared_dict "\%V\" is already defined as "

                           "\%V\"", &name, &ctx->name);

        return NGX_CONF_ERROR;

    }

    zone->init = ngx_http_lua_shdict_init_zone;

    zone->data = ctx;

    zp = ngx_array_push(lmcf->shdict_zones);

    if (zp == NULL) {

        return NGX_CONF_ERROR;

    }

    *zp = zone;

    lmcf->requires_shm = 1;

    return NGX_CONF_OK;

}

2.2 ngx_http_lua_shared_memory_add

ngx_shm_zone_t *

ngx_http_lua_shared_memory_add(ngx_conf_t *cf, ngx_str_t *name, size_t size,

    void *tag)

{

    ngx_http_lua_main_conf_t     *lmcf;

    ngx_shm_zone_t              **zp;

    ngx_shm_zone_t               *zone;

    ngx_http_lua_shm_zone_ctx_t  *ctx;

    ngx_int_t                     n;

    lmcf = ngx_http_conf_get_module_main_conf(cf, ngx_http_lua_module);

    if (lmcf == NULL) {

        return NULL;

    }

    if (lmcf->shm_zones == NULL) {

        lmcf->shm_zones = ngx_palloc(cf->pool, sizeof(ngx_array_t));

        if (lmcf->shm_zones == NULL) {

            return NULL;

        }

        if (ngx_array_init(lmcf->shm_zones, cf->pool, 2,

                           sizeof(ngx_shm_zone_t *))

            != NGX_OK)

        {

            return NULL;

        }

    }

    /* 分配一个代表共享内存的结构体 ngx_shm_zone_t，并将其插入到

     * cf->cycle->shared_memory 链表中 */

    zone = ngx_shared_memory_add(cf, name, (size_t) size, tag);

    if (zone == NULL) {

        return NULL;

    }

    if (zone->data) {

        ctx = (ngx_http_lua_shm_zone_ctx_t *) zone->data;

        return &ctx->zone;

    }

    n = sizeof(ngx_http_lua_shm_zone_ctx_t);

    ctx = ngx_pcalloc(cf->pool, n);

    if (ctx == NULL) {

        return NULL;

    }

    ctx->lmcf = lmcf;

    ctx->log = &cf->cycle->new_log;

    ctx->cycle = cf->cycle;

    ngx_memcpy(&ctx->zone, zone, sizeof(ngx_shm_zone_t));

    zp = ngx_array_push(lmcf->shm_zones);

    if (zp == NULL) {

        return NULL;

    }

    *zp = zone;

    /* 设置在 init_cycle 中真正创建共享内存时调用的初始化函数，

     * 该 init 函数是各个共享内存所特定的，根据使用方的自身需求不同

     * 而不同 */

    /* set zone init */

    zone->init = ngx_http_lua_shared_memory_init;

    zone->data = ctx;

    lmcf->requires_shm = 1;

    return &ctx->zone;

}

在 init_cycle 函数中：

{

    ...

    /* create shared memory */

    part = &cycle->shared_memory.part;

    shm_zone = part->elts;

    for (i = 0; /* void */ ; i++) {

        ...

        if (ngx_shm_alloc(&shm_zone[i].shm) != NGX_OK) {

            goto failed;

        }

        if (ngx_init_zone_pool(cycle, &shm_zone[i]) != NGX_OK) {

            goto failed;

        }

        /* 指向每个模块所创建的共享内存所特有的 init 函数 */

        if (shm_zone[i].init(&shm_zone[i], NULL) != NGX_OK) {

            goto failed;

        }

    }

    ...

}

对于 ngx_http_lua_module 模块的 lua_shared_dict 指令所创建的共享内存的 init 函数为 ngx_http_lua_shared_memory_init。

2.3 ngx_http_lua_shared_memory_init

static ngx_int_t

ngx_http_lua_shared_memory_init(ngx_shm_zone_t *shm_zone, void *data)

{

    ngx_http_lua_shm_zone_ctx_t *octx = data;

    ngx_shm_zone_t              *ozone;

    void                        *odata;

    ngx_int_t                    rc;

    volatile ngx_cycle_t        *saved_cycle;

    ngx_http_lua_main_conf_t    *lmcf;

    ngx_http_lua_shm_zone_ctx_t *ctx;

    ngx_shm_zone_t              *zone;

    ctx = (ngx_http_lua_shm_zone_ctx_t *) shm_zone->data;

    zone = &ctx->zone;

    odata = NULL;

    if (octx) {

        ozone = &octx->zone;

        odata = ozone->data;

    }

    zone->shm = shm_zone->shm;

#if defined(nginx_version) && nginx_version >= 1009000

    zone->noreuse = shm_zone->noreuse;

#endif

    /* 指向 ngx_http_lua_shdict_init_zone 函数 */

    if (zone->init(zone, odata) != NGX_OK) {

        return NGX_ERROR;

    }

    dd("get lmcf");

    lmcf = ctx->lmcf;

    if (lmcf == NULL) {

        return NGX_ERROR;

    }

    dd("lmcf->lua: %p", lmcf->lua);

    lmcf->shm_zones_inited++;

    if (lmcf->shm_zones_inited == lmcf->shm_zones->nelts

        && lmcf->init_handler)

    {

        saved_cycle = ngx_cycle;

        ngx_cycle = ctx->cycle;

        rc = lmcf->init_handler(ctx->log, lmcf, lmcf->lua);

        ngx_cycle = saved_cycle;

        if (rc != NGX_OK) {

            /* an error happened */

            return NGX_ERROR;

        }

    }

    return NGX_OK;

}

2.4 ngx_http_lua_shdict_init_zone

ngx_int_t

ngx_http_lua_shdict_init_zone(ngx_shm_zone_t *shm_zone, void *data)

{

    ngx_http_lua_shdict_ctx_t  *octx = data;

    size_t                      len;

    ngx_http_lua_shdict_ctx_t  *ctx;

    dd("init zone");

    ctx = shm_zone->data;

    if (octx) {

        ctx->sh = octx->sh;

        ctx->shpool = octx->shpool;

        return NGX_OK;

    }

    ctx->shpool = (ngx_slab_pool_t *) shm_zone->shm.addr;

    if (shm_zone->shm.exists) {

        ctx->sh = ctx->shpool->data;

        return NGX_OK;

    }

    ctx->sh = ngx_slab_alloc(ctx->shpool, sizeof(ngx_http_lua_shdict_shctx_t));

    if (ctx->sh == NULL) {

        return NGX_ERROR;

    }

    ctx->shpool->data = ctx->sh;

    ngx_rbtree_init(&ctx->sh->rbtree, &ctx->sh->sentinel,

                    ngx_http_lua_shdict_rbtree_insert_value);

    ngx_queue_init(&ctx->sh->lru_queue);

    len = sizeof(" in lua_shared_dict zone \"\"") + shm_zone->shm.name.len;

    ctx->shpool->log_ctx = ngx_slab_alloc(ctx->shpool, len);

    if (ctx->shpool->log_ctx == NULL) {

        return NGX_ERROR;

    }

    ngx_sprintf(ctx->shpool->log_ctx, " in lua_shared_dict zone \"%V\"%Z",

                &shm_zone->shm.name);

#if defined(nginx_version) && nginx_version >= 1005013

    ctx->shpool->log_nomem = 0;

#endif

    return NGX_OK;

}

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OpenResty之 lua_shared_dict 指令