ngx_http_lua_run_posted_thread

这个函数主要是为了ngx.thread.spawn的处理，ngx.thread.spawn生成新的"light thread"，这个"light thread"运行优先级比它的父协程高，会优先运行，父协程被迫暂停。"light thread"运行结束或者yield后，再由ngx_http_lua_run_posted_threads去运行父协程。

ngx.thread.spawn中创建"light thread"后， 调用ngx_http_lua_post_thread。

    if (ngx_http_lua_post_thread(r, ctx, ctx->cur_co_ctx) != NGX_OK) {return luaL_error(L, "no memory");}

ngx_http_lua_post_thread函数将父协程放在了ctx->posted_threads指向的链表中。

ngx_int_t
ngx_http_lua_post_thread(ngx_http_request_t *r, ngx_http_lua_ctx_t *ctx,ngx_http_lua_co_ctx_t *coctx)
{ngx_http_lua_posted_thread_t  **p;ngx_http_lua_posted_thread_t   *pt;pt = ngx_palloc(r->pool, sizeof(ngx_http_lua_posted_thread_t));if (pt == NULL) {return NGX_ERROR;}pt->co_ctx = coctx;pt->next = NULL;for (p = &ctx->posted_threads; *p; p = &(*p)->next) { /* void */ }*p = pt;return NGX_OK;
}

ngx_http_lua_run_posted_threads从ctx->posted_threads指向的链表中依次取出每个元素，调用ngx_http_lua_run_thread运行。

/* this is for callers other than the content handler */
ngx_int_t
ngx_http_lua_run_posted_threads(ngx_connection_t *c, lua_State *L,ngx_http_request_t *r, ngx_http_lua_ctx_t *ctx)
{ngx_int_t                        rc;ngx_http_lua_posted_thread_t    *pt;for ( ;; ) {if (c->destroyed) {return NGX_DONE;}pt = ctx->posted_threads;if (pt == NULL) {return NGX_DONE;}ctx->posted_threads = pt->next;ngx_http_lua_probe_run_posted_thread(r, pt->co_ctx->co,(int) pt->co_ctx->co_status);if (pt->co_ctx->co_status != NGX_HTTP_LUA_CO_RUNNING) {continue;}ctx->cur_co_ctx = pt->co_ctx;rc = ngx_http_lua_run_thread(L, r, ctx, 0);if (rc == NGX_AGAIN) {continue;}if (rc == NGX_DONE) {ngx_http_lua_finalize_request(r, NGX_DONE);continue;}/* rc == NGX_ERROR || rc >= NGX_OK */if (ctx->entered_content_phase) {ngx_http_lua_finalize_request(r, rc);}return rc;}/* impossible to reach here */
}

ngx_http_lua_run_thread使用方式

以lua-nginx-module的Access阶段的处理为例，实际的执行工作由ngx_http_lua_access_by_chunk函数中实现。 如下面的代码，调用ngx_http_lua_run_thread后根据返回值继续处理。

static ngx_int_t
ngx_http_lua_access_by_chunk(lua_State *L, ngx_http_request_t *r)
{/* 此处省去了创建协程的部分，只关注协程的运行  */rc = ngx_http_lua_run_thread(L, r, ctx, 0);dd("returned %d", (int) rc);if (rc == NGX_ERROR || rc > NGX_OK) {return rc;}c = r->connection;if (rc == NGX_AGAIN) {rc = ngx_http_lua_run_posted_threads(c, L, r, ctx);if (rc == NGX_ERROR || rc == NGX_DONE || rc > NGX_OK) {return rc;}if (rc != NGX_OK) {return NGX_DECLINED;}} else if (rc == NGX_DONE) {ngx_http_lua_finalize_request(r, NGX_DONE);rc = ngx_http_lua_run_posted_threads(c, L, r, ctx);if (rc == NGX_ERROR || rc == NGX_DONE || rc > NGX_OK) {return rc;}if (rc != NGX_OK) {return NGX_DECLINED;}}#if 1if (rc == NGX_OK) {if (r->header_sent) {dd("header already sent");/* response header was already generated in access_by_lua*,* so it is no longer safe to proceed to later phases* which may generate responses again */if (!ctx->eof) {dd("eof not yet sent");rc = ngx_http_lua_send_chain_link(r, ctx, NULL/* indicate last_buf */);if (rc == NGX_ERROR || rc > NGX_OK) {return rc;}}return NGX_HTTP_OK;}return NGX_OK;}
#endifreturn NGX_DECLINED;
}

ngx_http_lua_run_thread的返回值

函数ngx_http_lua_run_thread的返回值可分为下面几种

• NGX_OK
• NGX_AGAIN
• NGX_DONE
• NGX_ERROR: 执行出错
• 大于200: 响应的HTTP状态码

按照Nginx的处理规则，返回NGX_ERROR或大于200的HTTP状态码时，将会无条件结束当前请求的处理。 返回NGX_OK表明当前阶段处理完成，此时只需要调用ngx_http_lua_send_chain_link发送响应即可。重点关注的是NGX_AGAIN和NGX_DONE这两个。返回这两个值时都要调用ngx_http_lua_run_posted_thread来处理。

NGX_AGAIN

ngx_http_lua_run_thread什么时候会返回NGX_AGAIN?

• 1. ngx.sleep或ngx.socket等导致协程的yield
• 1. 调用ngx.thread导致当前请求对应的一个父协程和一个或多个"light thread"没有全部退出。 由于情况2的存在，需要调用ngx_http_lua_run_posted_thread进行处理。

NGX_DONE

在Nginx中，NGX_DONE表示对当前请求的处理已经告一段落了，但是请求还没有处理完成，之后的工作会有其他的模块进行。主要出现在三个地方

• 调用ngx_http_read_client_request_body读取请求包体时，由于从socket读取数据是异步的，会返回NGX_DONE。读取数据后对请求的处理由设置的回调函数执行
• 调用ngx_http_internal_redirect执行了内部跳转
• 创建子请求后，等待子请求完成后继续处理

在ngx_http_request_t中有一个作为引用计数的成员count。每次调用ngx_http_finalize_requet(r, NGX_DONE)时会将r的引用计数减一，减为0时才会真正结束当前请求。与此对应的模块返回NGX_DONE时都会有r->count++的操作。

在函数ngx_http_lua_access_by_chunk中当ngx_http_lua_run_thread返回NGX_DONE时(相比于返回值为NGX_AGAIN的情况)增加了一次ngx_http_finalize_request(r, NGX_DONE)的操作，就是为了将r的引用计数减一。

如果这里调用ngx_http_finalize_request(r, NGX_DONE)导致r的引用计数为0,将请求结束了，此时c->destory为true，再调用ngx_http_lua_run_posted_thread会直接返回。