Nginx进程分析（master_process篇）

<span style="font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);">首先看Nginx的主进程，主进程从main函数开始运行：</span>

int ngx_cdecl main(int argc, char *const *argv){    ngx_int_t         i;    ngx_log_t        *log;    ngx_cycle_t      *cycle, init_cycle;    ngx_core_conf_t  *ccf;    ngx_max_sockets = -1;// 初始化时钟模块，更新时钟（详见ngx_time_update）ngx_time_init();// 获取进程号    ngx_pid = ngx_getpid();// 初始化日志    log = ngx_log_init();    if (log == NULL) { return 1;}// 初始化Opensslngx_ssl_init(log);    ngx_memzero(&init_cycle, sizeof(ngx_cycle_t));    init_cycle.log = log;    ngx_cycle = &init_cycle;// 创建内存池    init_cycle.pool = ngx_create_pool(1024, log);    if (init_cycle.pool == NULL) { return 1; }// 保存argc和argv到ngx_argc和ngx_argv中    if (ngx_save_argv(&init_cycle, argc, argv) != NGX_OK) { return 1; }// 解析argv中的参数，部分作用于init_cycle    if (ngx_getopt(&init_cycle, argc, ngx_argv) != NGX_OK) { return 1; }// 这里的ngx_show_version、ngx_show_configure和ngx_test_config都是由ngx_getopt确定的    if (ngx_show_version) {        ngx_write_fd(ngx_stderr_fileno, "nginx version: " NGINX_VER CRLF,                     sizeof("nginx version: " NGINX_VER CRLF) - 1);        if (ngx_show_configure) { …… }        if (!ngx_test_config) { return 0; }    }    if (ngx_test_config) {        log->log_level = NGX_LOG_INFO;    }// 获取系统相关参数，例如pagesize和cpu个数；初始化随机种子    if (ngx_os_init(log) != NGX_OK) { return 1; }    if (ngx_crc32_init() != NGX_OK) { return 1; }// 如果获得了环境变量，就会初始化cycle. Listening，否则直接返回    if (ngx_add_inherited_sockets(&init_cycle) != NGX_OK) { return 1; }    ngx_max_module = 0;    for (i = 0; ngx_modules[i]; i++) {        ngx_modules[i]->index = ngx_max_module++;    }// 超级大的一个函数    cycle = ngx_init_cycle(&init_cycle);    if (cycle == NULL) {        if (ngx_test_config) {            ngx_log_error(NGX_LOG_EMERG, log, 0,                          "the configuration file %s test failed",                          init_cycle.conf_file.data);        }        return 1;    }    if (ngx_test_config) {        ngx_log_error(NGX_LOG_INFO, log, 0,                      "the configuration file %s was tested successfully",                      cycle->conf_file.data);        return 0;    }// 打印日志    ngx_os_status(cycle->log);    ngx_cycle = cycle;// 宏展开为ccf = cycle->conf_ctx[ngx_core_module.index];    ccf = (ngx_core_conf_t *) ngx_get_conf(cycle->conf_ctx, ngx_core_module);// ccf->master在ngx_core_module_init_conf中被设置为1    ngx_process = ccf->master ? NGX_PROCESS_MASTER : NGX_PROCESS_SINGLE;// 设置软中断（信号）处理函数ngx_signal_handler，该函数完成了对11种信号的处理    if (ngx_init_signals(cycle->log) != NGX_OK) { return 1; }    if (!ngx_inherited && ccf->daemon) {        if (ngx_daemon(cycle->log) != NGX_OK) {            return 1;        }        ngx_daemonized = 1;    }// 创建进程记录文件    if (ngx_create_pidfile(&ccf->pid, cycle->log) != NGX_OK) {        return 1;}    if (ngx_process == NGX_PROCESS_MASTER) {        ngx_master_process_cycle(cycle);    } else {        ngx_single_process_cycle(cycle);    }    return 0;}

main函数主要完成一系列初始化（详见注释），然后进入进程循环函数。根据输入参数的设置，可以进入主进程循环（ngx_master_process_cycle）或者单进程循环（ngx_single_process_cycle）。一般都是进入主进程循环。在该模式下，主进程会启动若干个（等于CPU核心数）工作进程用以完成相关计算。

下面是主进程真正进入主循环之前所做的工作：

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;    sigset_t           set;    struct itimerval   itv;    ngx_uint_t         live;    ngx_msec_t         delay;    ngx_listening_t   *ls;    ngx_core_conf_t   *ccf;// 屏蔽前述11种信号之10种（SIGPIPE除外，因为信号处理函数唯独对SIGPIPE没处理）    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_palloc(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);    ngx_start_worker_processes(cycle, ccf->worker_processes, NGX_PROCESS_RESPAWN);    ngx_start_garbage_collector(cycle, NGX_PROCESS_RESPAWN);

下面是master进程的主循环。进程每次等待信号到来，信号到来后首先被ngx_signal_handler处理，设置标志变量，然后进程被唤醒，根据标志变量执行相关操作，然后再次等待信号。注意主循环之前已屏蔽ngx_singal_handler中会被处理的信号，只在sigsuspend时解除屏蔽，保证了标志变量访问的互斥性。

    ngx_new_binary = 0;    delay = 0;    live = 1;    for ( ;; ) {<span style="white-space:pre"></span>// delay只在<span style="font-family: Arial, Helvetica, sans-serif;">ngx_terminate被置位后才被赋为非零值，然后在此基础上每次循环增加一倍，并添加一个定时器，在delay毫秒后唤醒该进程</span>        if (delay) {            delay *= 2;            ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,                           "temination 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);        ngx_time_update(0, 0);        ngx_log_debug0(NGX_LOG_DEBUG_EVENT, cycle->log, 0, "wake up");        if (ngx_reap) {            ngx_reap = 0;            ngx_log_debug0(NGX_LOG_DEBUG_EVENT, cycle->log, 0, "reap children");// 如果还有运行着的工作进程则返回1，否则返回0            live = ngx_reap_children(cycle);        }// 如果工作进程已死并且主进程终端或退出标志置位，则退出主进程        if (!live && (ngx_terminate || ngx_quit)) {            ngx_master_process_exit(cycle);        }        if (ngx_terminate) {            if (delay == 0) {                delay = 50;            }// 运行到这里说明工作进程没有全部退出，从delay=0开始依次间隔50ms、100ms、200ms、400ms、800ms向所有工作进程发送SIGTERM信号，最后一次直接发送SIGKILL强制终止工作进程。            if (delay > 1000) {                ngx_signal_worker_processes(cycle, SIGKILL);            } else {                ngx_signal_worker_processes(cycle,                                       ngx_signal_value(NGX_TERMINATE_SIGNAL));            }            continue;        }        if (ngx_quit) {// 向所有工作进程发送SIGQUIT信号            ngx_signal_worker_processes(cycle,                                        ngx_signal_value(NGX_SHUTDOWN_SIGNAL));// 关闭所有监听套接字            ls = cycle->listening.elts;            for (n = 0; n < cycle->listening.nelts; n++) {                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;        }        if (ngx_reconfigure) {            ngx_reconfigure = 0;// 另外再创建ccf->worker_processes个工作进程            if (ngx_new_binary) {                ngx_start_worker_processes(cycle, ccf->worker_processes,                                           NGX_PROCESS_RESPAWN);                ngx_start_garbage_collector(cycle, NGX_PROCESS_RESPAWN);                ngx_noaccepting = 0;                continue;            }            ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "reconfiguring");// 重新创建ccf->worker_processes个工作进程            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);            ngx_start_worker_processes(cycle, ccf->worker_processes,                                       NGX_PROCESS_JUST_RESPAWN);            ngx_start_garbage_collector(cycle, NGX_PROCESS_JUST_RESPAWN);            live = 1;            ngx_signal_worker_processes(cycle, ngx_signal_value(NGX_SHUTDOWN_SIGNAL));        }        if (ngx_restart) {            ngx_restart = 0;            ngx_start_worker_processes(cycle, ccf->worker_processes,                                       NGX_PROCESS_RESPAWN);            ngx_start_garbage_collector(cycle, NGX_PROCESS_RESPAWN);            live = 1;        }        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));        }        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);        }        if (ngx_noaccept) {            ngx_noaccept = 0;            ngx_noaccepting = 1;            ngx_signal_worker_processes(cycle,                                        ngx_signal_value(NGX_SHUTDOWN_SIGNAL));        }    }}

之前提到主进程首先会屏蔽信号处理函数中会被处理的信号，那么信号处理函数究竟会处理哪些信号，有时怎么处理，信号和主循环中的标志变量之间的对应关系是什么？所以我们看一看信号处理函数（由于我们暂时并不关心工作进程，因此下面只有主进程相关的信号处理）：

void ngx_signal_handler(int signo){    char            *action;    ngx_int_t        ignore;    ngx_err_t        err;    ngx_signal_t    *sig;    ignore = 0;    err = ngx_errno;    for (sig = signals; sig->signo != 0; sig++) {        if (sig->signo == signo) {            break;        }    }    ngx_time_update(0, 0);    action = "";    switch (ngx_process) {    case NGX_PROCESS_MASTER:    case NGX_PROCESS_SINGLE:        switch (signo) {        case ngx_signal_value(NGX_SHUTDOWN_SIGNAL):            ngx_quit = 1;            action = ", shutting down";            break;        case ngx_signal_value(NGX_TERMINATE_SIGNAL):        case SIGINT:            ngx_terminate = 1;            action = ", exiting";            break;        case ngx_signal_value(NGX_NOACCEPT_SIGNAL):            ngx_noaccept = 1;            action = ", stop accepting connections";            break;        case ngx_signal_value(NGX_RECONFIGURE_SIGNAL):            ngx_reconfigure = 1;            action = ", reconfiguring";            break;        case ngx_signal_value(NGX_REOPEN_SIGNAL):            ngx_reopen = 1;            action = ", reopening logs";            break;        case ngx_signal_value(NGX_CHANGEBIN_SIGNAL):            if (getppid() > 1 || ngx_new_binary > 0) {                /*                 * Ignore the signal in the new binary if its parent is                 * not the init process, i.e. the old binary's process                 * is still running.  Or ignore the signal in the old binary's                 * process if the new binary's process is already running.                 */                action = ", ignoring";                ignore = 1;                break;            }            ngx_change_binary = 1;            action = ", changing binary";            break;        case SIGALRM:            break;        case SIGIO:            ngx_sigio = 1;            break;        case SIGCHLD:            ngx_reap = 1;            break;        }        break;    case NGX_PROCESS_WORKER:        ...        break;    }    ...    if (signo == SIGCHLD) {        ngx_process_get_status();    }    ngx_set_errno(err);}

NGX_SHUTDOWN_SIGNAL（SIGQUIT）信号会将ngx_quit变量置一。NGX_TERMINATE_SIGNAL（SIGTERM）和SIGINT信号对于主进程没有区别，都是将ngx_terminate置一。NGX_NOACCEPT_SIGNAL（SIGWINCE）信号会将ngx_noaccept变量置一。NGX_RECONFIGURE_SIGNAL（SIGHUP）信号会将ngx_reconfigure变量置一。NGX_REOPEN_SIGNAL（SIGUSR1）会将ngx_reopen变量置一。NGX_CHANGEBIN_SIGNAL（SIGUSR2）信号会将ngx_change_binary变量置一，这时需要注意，如果一个新的（Nginx）程序的父进程不是init进程，也就是说新程序的父进程仍然是旧程序，旧程序并没有死掉，就忽略该信号，Nginx并不希望在一台主机上运行着两个程序。SIGIO信号会将ngx_sigio变量置一。SIGCHLD会将ngx_reap变量置一。SIGALRM信号不做任何处理，将最终唤醒进程执行定时器的相关响应。SIGPIPE信号没有出现，直接忽略。

我们首先来看SIGCHLD信号，对应着ngx_reap，在主循环中如果ngx_reap置一则调用ngx_reap_children函数。子进程结束时，父进程就会收到SIGCHLD信号。所以ngx_reap主要做的是：关闭与该子进程（工作进程）通信的管道；通知其他所有（工作）进程该工作进程退出的消息；对于需要重启的则重启该工作进程（守护功能），同时也要通知其他进程；从进程数组中移除该进程。

static ngx_uint_t ngx_reap_children(ngx_cycle_t *cycle){    ngx_int_t         i, n;    ngx_uint_t        live;    ngx_channel_t     ch;    ngx_core_conf_t  *ccf;    ch.command = NGX_CMD_CLOSE_CHANNEL;    ch.fd = -1;    live = 0;    for (i = 0; i < ngx_last_process; i++) {        if (ngx_processes[i].pid == -1) {            continue;        }        if (ngx_processes[i].exited) {            if (!ngx_processes[i].detached) {// 关闭读管道                ngx_close_channel(ngx_processes[i].channel, cycle->log);                ngx_processes[i].channel[0] = -1;                ngx_processes[i].channel[1] = -1;                ch.pid = ngx_processes[i].pid;                ch.slot = i;// 通知其他所有进程该进程已退出，因为工作进程都是通过fork产生的，所以它们都有和主进程一样的该进程管道句柄，需要关闭                for (n = 0; n < ngx_last_process; n++) {                    if (ngx_processes[n].exited                        || ngx_processes[n].pid == -1                        || ngx_processes[n].channel[0] == -1)                    {                        continue;                    }                    ngx_write_channel(ngx_processes[n].channel[0],                                      &ch, sizeof(ngx_channel_t), cycle->log);                }            }// 需要重启的进程则调用ngx_spawn_process重启。            if (ngx_processes[i].respawn                && !ngx_processes[i].exiting                && !ngx_terminate                && !ngx_quit)            {                if (ngx_spawn_process(cycle, ngx_processes[i].proc,                                      ngx_processes[i].data,                                      ngx_processes[i].name, i)                    == NGX_INVALID_PID)                {                    continue;                }                ch.command = NGX_CMD_OPEN_CHANNEL;                ch.pid = ngx_processes[ngx_process_slot].pid;                ch.slot = ngx_process_slot;                ch.fd = ngx_processes[ngx_process_slot].channel[0];// 通知其他所有进程，新进程已创建，与上面的类似，也需要设置新进程ID和管道描述符                for (n = 0; n < ngx_last_process; n++) {                    if (n == ngx_process_slot                        || ngx_processes[n].pid == -1                        || ngx_processes[n].channel[0] == -1)                    {                        continue;                    }                    ngx_write_channel(ngx_processes[n].channel[0],                                      &ch, sizeof(ngx_channel_t), cycle->log);                }                live = 1;                continue;            }            if (ngx_processes[i].pid == ngx_new_binary) {                ccf = (ngx_core_conf_t *) ngx_get_conf(cycle->conf_ctx,                                                       ngx_core_module);                if (ngx_rename_file((char *) ccf->oldpid.data,                                    (char *) ccf->pid.data)                    != NGX_OK)                {}                ngx_new_binary = 0;                if (ngx_noaccepting) {                    ngx_restart = 1;                    ngx_noaccepting = 0;                }            }// 移除该进程            if (i == ngx_last_process - 1) {                ngx_last_process--;            } else {                ngx_processes[i].pid = -1;            }        } else if (ngx_processes[i].exiting || !ngx_processes[i].detached) {            live = 1;        }    }    return live;}

在主循环中，如果ngx_terminate或ngx_quit变量被置一，并且没有工作进程仍在运行，则会调用ngx_master_process_exit函数负责退出主进程。

static void ngx_master_process_exit(ngx_cycle_t *cycle){    ngx_uint_t  i;    ngx_delete_pidfile(cycle);    ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "exit");    for (i = 0; ngx_modules[i]; i++) {        if (ngx_modules[i]->exit_master) {            ngx_modules[i]->exit_master(cycle);        }    }    /*     * Copy ngx_cycle->log related data to the special static exit cycle,     * log, and log file structures enough to allow a signal handler to log.     * The handler may be called when standard ngx_cycle->log allocated from     * ngx_cycle->pool is already destroyed.     */    ngx_exit_log_file.fd = ngx_cycle->log->file->fd;    ngx_exit_log = *ngx_cycle->log;    ngx_exit_log.file = &ngx_exit_log_file;    ngx_exit_cycle.log = &ngx_exit_log;    ngx_cycle = &ngx_exit_cycle;    ngx_destroy_pool(cycle->pool);    exit(0);}