Nginx事件驱动框架处理流程是什么

voidngx_event_accept(ngx_event_t *ev){ socklen_t  socklen; ngx_err_t  err; ngx_log_t  *log; ngx_uint_t  level; ngx_socket_t  s; ngx_event_t  *rev, *wev; ngx_listening_t  *ls; ngx_connection_t *c, *lc; ngx_event_conf_t *ecf; u_char  sa[ngx_sockaddrlen];  if (ev->timedout) {  if (ngx_enable_accept_events((ngx_cycle_t *) ngx_cycle) != ngx_ok) {   return;  }   ev->timedout = 0; }  ecf = ngx_event_get_conf(ngx_cycle->conf_ctx, ngx_event_core_module);  if (ngx_event_flags & ngx_use_rtsig_event) {  ev->available = 1;  } else if (!(ngx_event_flags & ngx_use_kqueue_event)) {  ev->available = ecf->multi_accept; }  lc = ev->data; ls = lc->listening; ev->ready = 0;  do {  socklen = ngx_sockaddrlen;   /* 1、accept方法试图建立连接，非阻塞调用 */  s = accept(lc->fd, (struct sockaddr *) sa, &socklen);   if (s == (ngx_socket_t) -1)  {   err = ngx_socket_errno;    if (err == ngx_eagain)   {    /* 没有连接，直接返回 */    return;   }    level = ngx_log_alert;    if (err == ngx_econnaborted) {    level = ngx_log_err;    } else if (err == ngx_emfile || err == ngx_enfile) {    level = ngx_log_crit;   }    if (err == ngx_econnaborted) {    if (ngx_event_flags & ngx_use_kqueue_event) {     ev->available--;    }     if (ev->available) {     continue;    }   }    if (err == ngx_emfile || err == ngx_enfile) {    if (ngx_disable_accept_events((ngx_cycle_t *) ngx_cycle)     != ngx_ok)    {     return;    }     if (ngx_use_accept_mutex) {     if (ngx_accept_mutex_held) {      ngx_shmtx_unlock(&ngx_accept_mutex);      ngx_accept_mutex_held = 0;     }      ngx_accept_disabled = 1;     } else {     ngx_add_timer(ev, ecf->accept_mutex_delay);    }   }    return;  }   /* 2、设置负载均衡阈值 */  ngx_accept_disabled = ngx_cycle->connection_n / 8        - ngx_cycle->free_connection_n;   /* 3、从连接池获得一个连接对象 */  c = ngx_get_connection(s, ev->log);   /* 4、为连接创建内存池 */  c->pool = ngx_create_pool(ls->pool_size, ev->log);   c->sockaddr = ngx_palloc(c->pool, socklen);   ngx_memcpy(c->sockaddr, sa, socklen);   log = ngx_palloc(c->pool, sizeof(ngx_log_t));   /* set a blocking mode for aio and non-blocking mode for others */  /* 5、设置套接字属性为阻塞或非阻塞 */  if (ngx_inherited_nonblocking) {   if (ngx_event_flags & ngx_use_aio_event) {    if (ngx_blocking(s) == -1) {     ngx_log_error(ngx_log_alert, ev->log, ngx_socket_errno,         ngx_blocking_n " failed");     ngx_close_accepted_connection(c);     return;    }   }   } else {   if (!(ngx_event_flags & (ngx_use_aio_event|ngx_use_rtsig_event))) {    if (ngx_nonblocking(s) == -1) {     ngx_log_error(ngx_log_alert, ev->log, ngx_socket_errno,         ngx_nonblocking_n " failed");     ngx_close_accepted_connection(c);     return;    }   }  }   *log = ls->log;   c->recv = ngx_recv;  c->send = ngx_send;  c->recv_chain = ngx_recv_chain;  c->send_chain = ngx_send_chain;   c->log = log;  c->pool->log = log;   c->socklen = socklen;  c->listening = ls;  c->local_sockaddr = ls->sockaddr;  c->local_socklen = ls->socklen;   c->unexpected_eof = 1;   rev = c->read;  wev = c->write;   wev->ready = 1;   if (ngx_event_flags & (ngx_use_aio_event|ngx_use_rtsig_event)) {   /* rtsig, aio, iocp */   rev->ready = 1;  }   if (ev->deferred_accept) {   rev->ready = 1;   }   rev->log = log;  wev->log = log;   /*   * todo: mt: - ngx_atomic_fetch_add()   *  or protection by critical section or light mutex   *   * todo: mp: - allocated in a shared memory   *   - ngx_atomic_fetch_add()   *  or protection by critical section or light mutex   */   c->number = ngx_atomic_fetch_add(ngx_connection_counter, 1);   if (ls->addr_ntop) {   c->addr_text.data = ngx_pnalloc(c->pool, ls->addr_text_max_len);   if (c->addr_text.data == null) {    ngx_close_accepted_connection(c);    return;   }    c->addr_text.len = ngx_sock_ntop(c->sockaddr, c->socklen,            c->addr_text.data,            ls->addr_text_max_len, 0);   if (c->addr_text.len == 0) {    ngx_close_accepted_connection(c);    return;   }  }   /* 6、将新连接对应的读写事件添加到epoll对象中 */  if (ngx_add_conn && (ngx_event_flags & ngx_use_epoll_event) == 0) {   if (ngx_add_conn(c) == ngx_error) {    ngx_close_accepted_connection(c);    return;   }  }   log->data = null;  log->handler = null;   /* 7、tcp建立成功调用的方法，这个方法在ngx_listening_t结构体中 */  ls->handler(c);  } while (ev->available); /* available标志表示一次尽可能多的建立连接，由配置项multi_accept决定 */}

if (flags & ngx_post_events){ /* 延后处理这批事件 */ queue = (ngx_event_t **) (rev->accept ? &ngx_posted_accept_events : &ngx_posted_events);  /* 将事件添加到延后执行队列中 */ ngx_locked_post_event(rev, queue);}else{ rev->handler(rev); /* 不需要延后，则立即处理事件 */}

if (ngx_accept_disabled > 0){  ngx_accept_disabled--;}else{ if (ngx_trylock_accept_mutex(cycle) == ngx_error) {  return; } ....}