Nginx学习之六-nginx核心进程模型

一、Nginx整体架构

正常执行中的nginx会有多个进程，最基本的有master process（监控进程，也叫做主进程）和woker process（工作进程），还可能有cache相关进程。

一个较为完整的整体框架结构如图所示：

二、核心进程模型

启动nginx的主进程将充当监控进程，而由主进程fork()出来的子进程则充当工作进程。

nginx也可以单进程模型执行，在这种进程模型下，主进程就是工作进程，没有监控进程。

Nginx的核心进程模型框图如下：

master进程

监控进程充当整个进程组与用户的交互接口，同时对进程进行监护。它不需要处理网络事件，不负责业务的执行，只会通过管理worker进程来实现重启服务、平滑升级、更换日志文件、配置文件实时生效等功能。

master进程全貌图（来自阿里集团数据平台博客）：

master进程中for(::)无限循环内有一个关键的sigsuspend()函数调用，该函数调用是的master进程的大部分时间都处于挂起状态，直到master进程收到信号为止。

master进程通过检查一下7个标志位来决定ngx_master_process_cycle方法的运行：

sig_atomic_t ngx_reap;

sig_atomic_t ngx_terminate;

sig_atomic_t ngx_quit;

sig_atomic_t ngx_reconfigure;

sig_atomic_t ngx_reopen;

sig_atomic_t ngx_change_binary;

sig_atomic_t ngx_noaccept;

进程中接收到的信号对Nginx框架的意义：

信号	对应进程中的全局标志位变量	意义
QUIT	ngx_quit	优雅地关闭整个服务
TERM或INT	ngx_terminate	强制关闭整个服务
USR1	ngx_reopen	重新打开服务中的所有文件
WINCH	ngx_noaccept	所有子进程不再接受处理新的连接，实际相当于对所有子进程发送QUIT信号
USR2	ngx_change_binary	平滑升级到新版本的Nginx程序
HUP	ng_reconfigure	重读配置文件
CHLD	ngx_reap	有子进程以外结束，需要监控所有子进程

还有一个标志位会用到：ngx_restart，它仅仅是在master工作流程中作为标志位使用，与信号无关。

核心代码（ngx_process_cycle.c）：

 void
 ngx_master_process_cycle(ngx_cycle_t *cycle)
 {
     char              *title;
     u_char            *p;
     size_t             size;
     ngx_int_t          i;
     ngx_uint_t         n, sigio;
     sigset_t           set;
     struct itimerval   itv;
     ngx_uint_t         live;
     ngx_msec_t         delay;
     ngx_listening_t   *ls;
     ngx_core_conf_t   *ccf;

     //信号处理设置工作
     sigemptyset(&set);
     sigaddset(&set, SIGCHLD);
     sigaddset(&set, SIGALRM);
     sigaddset(&set, SIGIO);
     sigaddset(&set, SIGINT);
     sigaddset(&set, ngx_signal_value(NGX_RECONFIGURE_SIGNAL));
     sigaddset(&set, ngx_signal_value(NGX_REOPEN_SIGNAL));
     sigaddset(&set, ngx_signal_value(NGX_NOACCEPT_SIGNAL));
     sigaddset(&set, ngx_signal_value(NGX_TERMINATE_SIGNAL));
     sigaddset(&set, ngx_signal_value(NGX_SHUTDOWN_SIGNAL));
     sigaddset(&set, ngx_signal_value(NGX_CHANGEBIN_SIGNAL));

     if (sigprocmask(SIG_BLOCK, &set, NULL) == -1) {
         ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
                       "sigprocmask() failed");
     }

     sigemptyset(&set);


     size = sizeof(master_process);

     for (i = 0; i < ngx_argc; i++) {
         size += ngx_strlen(ngx_argv[i]) + 1;
     }

     title = ngx_pnalloc(cycle->pool, size);

     p = ngx_cpymem(title, master_process, sizeof(master_process) - 1);
     for (i = 0; i < ngx_argc; i++) {
         *p++ = ' ';
         p = ngx_cpystrn(p, (u_char *) ngx_argv[i], size);
     }

     ngx_setproctitle(title);


     ccf = (ngx_core_conf_t *) ngx_get_conf(cycle->conf_ctx, ngx_core_module);

     //其中包含了fork产生子进程的内容
     ngx_start_worker_processes(cycle, ccf->worker_processes,
                                NGX_PROCESS_RESPAWN);
     //Cache管理进程与cache加载进程的主流程
     ngx_start_cache_manager_processes(cycle, 0);

     ngx_new_binary = 0;
     delay = 0;
     sigio = 0;
     live = 1;

     for ( ;; ) {//循环
         if (delay) {
             if (ngx_sigalrm) {
                 sigio = 0;
                 delay *= 2;
                 ngx_sigalrm = 0;
             }

             ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
                            "termination cycle: %d", delay);

             itv.it_interval.tv_sec = 0;
             itv.it_interval.tv_usec = 0;
             itv.it_value.tv_sec = delay / 1000;
             itv.it_value.tv_usec = (delay % 1000 ) * 1000;

             if (setitimer(ITIMER_REAL, &itv, NULL) == -1) {
                 ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
                               "setitimer() failed");
             }
         }

         ngx_log_debug0(NGX_LOG_DEBUG_EVENT, cycle->log, 0, "sigsuspend");

         sigsuspend(&set);//master进程休眠，等待接受信号被激活

         ngx_time_update();

         ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
                        "wake up, sigio %i", sigio);

         //标志位为1表示需要监控所有子进程
         if (ngx_reap) {
             ngx_reap = 0;
             ngx_log_debug0(NGX_LOG_DEBUG_EVENT, cycle->log, 0, "reap children");

             live = ngx_reap_children(cycle);//管理子进程
         }

         //当live标志位为0（表示所有子进程已经退出）、ngx_terminate标志位为1或者ngx_quit标志位为1表示要退出master进程
         if (!live && (ngx_terminate || ngx_quit)) {
             ngx_master_process_exit(cycle);//退出master进程
         }

         //ngx_terminate标志位为1，强制关闭服务，发送TERM信号到所有子进程
         if (ngx_terminate) {
             if (delay == 0) {
                 delay = 50;
             }

             if (sigio) {
                 sigio--;
                 continue;
             }

             sigio = ccf->worker_processes + 2 /* cache processes */;

             if (delay > 1000) {
                 ngx_signal_worker_processes(cycle, SIGKILL);
             } else {
                 ngx_signal_worker_processes(cycle,
                                        ngx_signal_value(NGX_TERMINATE_SIGNAL));
             }

             continue;
         }

         //ngx_quit标志位为1，优雅的关闭服务
         if (ngx_quit) {
             ngx_signal_worker_processes(cycle,
                                         ngx_signal_value(NGX_SHUTDOWN_SIGNAL));//向所有子进程发送quit信号

             ls = cycle->listening.elts;
             for (n = 0; n < cycle->listening.nelts; n++) {//关闭监听端口
                 if (ngx_close_socket(ls[n].fd) == -1) {
                     ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_socket_errno,
                                   ngx_close_socket_n " %V failed",
                                   &ls[n].addr_text);
                 }
             }
             cycle->listening.nelts = 0;

             continue;
         }

         //ngx_reconfigure标志位为1，重新读取配置文件
         //nginx不会让原来的worker子进程再重新读取配置文件，其策略是重新初始化ngx_cycle_t结构体，用它来读取新的额配置文件
         //再创建新的额worker子进程，销毁旧的worker子进程
         if (ngx_reconfigure) {
             ngx_reconfigure = 0;

             //ngx_new_binary标志位为1，平滑升级Nginx
             if (ngx_new_binary) {
                 ngx_start_worker_processes(cycle, ccf->worker_processes,
                                            NGX_PROCESS_RESPAWN);
                 ngx_start_cache_manager_processes(cycle, 0);
                 ngx_noaccepting = 0;

                 continue;
             }

             ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "reconfiguring");

             //初始化ngx_cycle_t结构体
             cycle = ngx_init_cycle(cycle);
             if (cycle == NULL) {
                 cycle = (ngx_cycle_t *) ngx_cycle;
                 continue;
             }

             ngx_cycle = cycle;
             ccf = (ngx_core_conf_t *) ngx_get_conf(cycle->conf_ctx,
                                                    ngx_core_module);
             //创建新的worker子进程
             ngx_start_worker_processes(cycle, ccf->worker_processes,
                                        NGX_PROCESS_JUST_RESPAWN);
             ngx_start_cache_manager_processes(cycle, 1);

             /* allow new processes to start */
             ngx_msleep(100);

             live = 1;
             //向所有子进程发送QUIT信号
             ngx_signal_worker_processes(cycle,
                                         ngx_signal_value(NGX_SHUTDOWN_SIGNAL));
         }
         //ngx_restart标志位在ngx_noaccepting（表示正在停止接受新的连接）为1的时候被设置为1.
         //重启子进程
         if (ngx_restart) {
             ngx_restart = 0;
             ngx_start_worker_processes(cycle, ccf->worker_processes,
                                        NGX_PROCESS_RESPAWN);
             ngx_start_cache_manager_processes(cycle, 0);
             live = 1;
         }

         //ngx_reopen标志位为1，重新打开所有文件
         if (ngx_reopen) {
             ngx_reopen = 0;
             ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "reopening logs");
             ngx_reopen_files(cycle, ccf->user);
             ngx_signal_worker_processes(cycle,
                                         ngx_signal_value(NGX_REOPEN_SIGNAL));
         }

         //平滑升级Nginx
         if (ngx_change_binary) {
             ngx_change_binary = 0;
             ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "changing binary");
             ngx_new_binary = ngx_exec_new_binary(cycle, ngx_argv);
         }

         //ngx_noaccept为1，表示所有子进程不再处理新的连接
         if (ngx_noaccept) {
             ngx_noaccept = 0;
             ngx_noaccepting = 1;
             ngx_signal_worker_processes(cycle,
                                         ngx_signal_value(NGX_SHUTDOWN_SIGNAL));
         }
     }
 }

ngx_start_worker_processes函数：

 static void
 ngx_start_worker_processes(ngx_cycle_t *cycle, ngx_int_t n, ngx_int_t type)
 {
     ngx_int_t      i;
     ngx_channel_t  ch;

     ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "start worker processes");

     ch.command = NGX_CMD_OPEN_CHANNEL;

     //循环创建n个worker子进程
     for (i = 0; i < n; i++) {
         //完成fok新进程的具体工作
         ngx_spawn_process(cycle, ngx_worker_process_cycle,
                           (void *) (intptr_t) i, "worker process", type);

         //全局数组ngx_processes就是用来存储每个子进程的相关信息，如：pid，channel，进程做具体事情的接口指针等等，这些信息就是用结构体ngx_process_t来描述的。
         ch.pid = ngx_processes[ngx_process_slot].pid;
         ch.slot = ngx_process_slot;
         ch.fd = ngx_processes[ngx_process_slot].channel[0];

         /*在ngx_spawn_process创建好一个worker进程返回后，master进程就将worker进程的pid、worker进程在ngx_processes数组中的位置及channel[0]传递给前面已经创建好的worker进程，然后继续循环开始创建下一个worker进程。刚提到一个channel[0]，这里简单说明一下：channel就是一个能够存储2个整型元素的数组而已，这个channel数组就是用于socketpair函数创建一个进程间通道之用的。master和worker进程以及worker进程之间都可以通过这样的一个通道进行通信，这个通道就是在ngx_spawn_process函数中fork之前调用socketpair创建的。*/
         ngx_pass_open_channel(cycle, &ch);
     }
 }

ngx_spawn_process函数：

 //参数解释：
 //cycle：nginx框架所围绕的核心结构体
 //proc：子进程中将要执行的工作循环
 //data：参数
 //name：子进程名字
 ngx_pid_t
 ngx_spawn_process(ngx_cycle_t *cycle, ngx_spawn_proc_pt proc, void *data,
     char *name, ngx_int_t respawn)
 {
     u_long     on;
     ngx_pid_t  pid;
     ngx_int_t  s;

     if (respawn >= 0) {
         s = respawn;

     } else {
         for (s = 0; s < ngx_last_process; s++) {
             if (ngx_processes[s].pid == -1) {
                 break;
             }
         }

         if (s == NGX_MAX_PROCESSES) {
             ngx_log_error(NGX_LOG_ALERT, cycle->log, 0,
                           "no more than %d processes can be spawned",
                           NGX_MAX_PROCESSES);
             return NGX_INVALID_PID;
         }
     }


     if (respawn != NGX_PROCESS_DETACHED) {

         /* Solaris 9 still has no AF_LOCAL */
         //创建父子进程间通信的套接字对（基于TCP）
         if (socketpair(AF_UNIX, SOCK_STREAM, 0, ngx_processes[s].channel) == -1)
         {
             ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
                           "socketpair() failed while spawning \"%s\"", name);
             return NGX_INVALID_PID;
         }

         ngx_log_debug2(NGX_LOG_DEBUG_CORE, cycle->log, 0,
                        "channel %d:%d",
                        ngx_processes[s].channel[0],
                        ngx_processes[s].channel[1]);

         //设置为非阻塞模式
         if (ngx_nonblocking(ngx_processes[s].channel[0]) == -1) {
             ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
                           ngx_nonblocking_n " failed while spawning \"%s\"",
                           name);
             ngx_close_channel(ngx_processes[s].channel, cycle->log);
             return NGX_INVALID_PID;
         }

         if (ngx_nonblocking(ngx_processes[s].channel[1]) == -1) {
             ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
                           ngx_nonblocking_n " failed while spawning \"%s\"",
                           name);
             ngx_close_channel(ngx_processes[s].channel, cycle->log);
             return NGX_INVALID_PID;
         }

         on = 1;
         if (ioctl(ngx_processes[s].channel[0], FIOASYNC, &on) == -1) {
             ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
                           "ioctl(FIOASYNC) failed while spawning \"%s\"", name);
             ngx_close_channel(ngx_processes[s].channel, cycle->log);
             return NGX_INVALID_PID;
         }

         if (fcntl(ngx_processes[s].channel[0], F_SETOWN, ngx_pid) == -1) {
             ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
                           "fcntl(F_SETOWN) failed while spawning \"%s\"", name);
             ngx_close_channel(ngx_processes[s].channel, cycle->log);
             return NGX_INVALID_PID;
         }

         if (fcntl(ngx_processes[s].channel[0], F_SETFD, FD_CLOEXEC) == -1) {
             ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
                           "fcntl(FD_CLOEXEC) failed while spawning \"%s\"",
                            name);
             ngx_close_channel(ngx_processes[s].channel, cycle->log);
             return NGX_INVALID_PID;
         }

         if (fcntl(ngx_processes[s].channel[1], F_SETFD, FD_CLOEXEC) == -1) {
             ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
                           "fcntl(FD_CLOEXEC) failed while spawning \"%s\"",
                            name);
             ngx_close_channel(ngx_processes[s].channel, cycle->log);
             return NGX_INVALID_PID;
         }

         ngx_channel = ngx_processes[s].channel[1];

     } else {
         ngx_processes[s].channel[0] = -1;
         ngx_processes[s].channel[1] = -1;
     }

     ngx_process_slot = s;

     //创建子进程
     pid = fork();

     switch (pid) {

     case -1:
         ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
                       "fork() failed while spawning \"%s\"", name);
         ngx_close_channel(ngx_processes[s].channel, cycle->log);
         return NGX_INVALID_PID;

     case 0:
         ngx_pid = ngx_getpid();
         proc(cycle, data);
         break;

     default:
         break;
     }

     ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "start %s %P", name, pid);

     ngx_processes[s].pid = pid;
     ngx_processes[s].exited = 0;

     if (respawn >= 0) {
         return pid;
     }

     ngx_processes[s].proc = proc;
     ngx_processes[s].data = data;
     ngx_processes[s].name = name;
     ngx_processes[s].exiting = 0;

     switch (respawn) {

     case NGX_PROCESS_NORESPAWN:
         ngx_processes[s].respawn = 0;
         ngx_processes[s].just_spawn = 0;
         ngx_processes[s].detached = 0;
         break;

     case NGX_PROCESS_JUST_SPAWN:
         ngx_processes[s].respawn = 0;
         ngx_processes[s].just_spawn = 1;
         ngx_processes[s].detached = 0;
         break;

     case NGX_PROCESS_RESPAWN:
         ngx_processes[s].respawn = 1;
         ngx_processes[s].just_spawn = 0;
         ngx_processes[s].detached = 0;
         break;

     case NGX_PROCESS_JUST_RESPAWN:
         ngx_processes[s].respawn = 1;
         ngx_processes[s].just_spawn = 1;
         ngx_processes[s].detached = 0;
         break;

     case NGX_PROCESS_DETACHED:
         ngx_processes[s].respawn = 0;
         ngx_processes[s].just_spawn = 0;
         ngx_processes[s].detached = 1;
         break;
     }

     if (s == ngx_last_process) {
         ngx_last_process++;
     }

     return pid;
 }

worker进程

worker进程的主要任务是完成具体的任务逻辑。其主要关注点是与客户端或后端真实服务器（此时nginx作为中间代理）之间的数据可读/可写等I/O交互事件，所以工作进程的阻塞点是在像select()、epoll_wait()等这样的I/O多路复用函数调用处，以等待发生数据可读/写事件。当然也可能被新收到的进程信号中断。

master进程如何通通知worker进程去做某些工作呢？采用的是信号。

当收到信号时，信号处理函数ngx_signal_handler()就会执行。

对于worker进程的工作方法ngx_worker_process_cycle来说，它主要关注4个全局标志位：

sig_atomic_t ngx_terminate;//强制关闭进程

sig_atomic_t ngx_quit;//优雅地关闭进程（有唯一一段代码会设置它，就是接受到QUIT信号。ngx_quit只有在首次设置为1,时，才会将ngx_exiting置为1）

ngx_uint_t ngx_exiting;//退出进程标志位

sig_atomic_t ngx_reopen;//重新打开所有文件

其中ngx_terminate、ngx_quit 、ngx_reopen都将由ngx_signal_handler根据接受到的信号来设置。ngx_exiting标志位仅由ngx_worker_cycle方法在退出时作为标志位使用。

核心代码（ngx_process_cycle.c）：

 static void
 ngx_worker_process_cycle(ngx_cycle_t *cycle, void *data)
 {
     ngx_int_t worker = (intptr_t) data;

     ngx_uint_t         i;
     ngx_connection_t  *c;

     ngx_process = NGX_PROCESS_WORKER;

     //子进程初始化
     ngx_worker_process_init(cycle, worker);

     ngx_setproctitle("worker process");

 //这里有一段多线程条件下的代码。由于nginx并不支持多线程，因此删除掉了

     //循环
     for ( ;; ) {

         //ngx_exiting标志位为1，进程退出
         if (ngx_exiting) {
             c = cycle->connections;
             for (i = 0; i < cycle->connection_n; i++) {
                 if (c[i].fd != -1 && c[i].idle) {
                     c[i].close = 1;
                     c[i].read->handler(c[i].read);
                 }
             }

             if (ngx_event_timer_rbtree.root == ngx_event_timer_rbtree.sentinel)
             {
                 ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "exiting");
                 ngx_worker_process_exit(cycle);
             }
         }

         ngx_log_debug0(NGX_LOG_DEBUG_EVENT, cycle->log, 0, "worker cycle");

         ngx_process_events_and_timers(cycle);//处理事件的方法

         //强制结束进程
         if (ngx_terminate) {
             ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "exiting");
             ngx_worker_process_exit(cycle);
         }

         //优雅地退出进程
         if (ngx_quit) {
             ngx_quit = 0;
             ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0,
                           "gracefully shutting down");
             ngx_setproctitle("worker process is shutting down");

             if (!ngx_exiting) {
                 ngx_close_listening_sockets(cycle);
                 //设置ngx_exiting 标志位
                 ngx_exiting = 1;
             }
         }

         //重新打开所有文件
         if (ngx_reopen) {
             ngx_reopen = 0;
             ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "reopening logs");
             ngx_reopen_files(cycle, -1);
         }