默认情况下，Nginx都是多进程的运行模式。Nginx和Memcached不一样，是多进程的模式。采用多进程模式最大的好处：

1. 每个进程的资源独立

2. 不需要添加各种繁琐的锁了



Nginx多进程具体实现

1. ngx_master_process_cycle 进入多进程模式

ngx_master_process_cycle方法主要做了两个工作：

1. 主进程进行信号的监听和处理

2. 开启子进程

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;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);if (title == NULL) {exit(2);}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_cache_manager_processes(cycle, 0);ngx_new_binary = 0;delay = 0;sigio = 0;live = 1;for (;;) {if (delay) {if (ngx_sigalrm) {sigio = 0;delay *= 2;ngx_sigalrm = 0;}ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,"termination cycle: %M", 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();ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,"wake up, sigio %i", sigio);if (ngx_reap) {ngx_reap = 0;ngx_log_debug0(NGX_LOG_DEBUG_EVENT, cycle->log, 0, "reap children");live = ngx_reap_children(cycle);}if (!live && (ngx_terminate || ngx_quit)) {ngx_master_process_exit(cycle);}if (ngx_terminate) {if (delay == 0) {delay = 50;}if (sigio) {sigio--;continue;}sigio = ccf->worker_processes + 2 ;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) {ngx_signal_worker_processes(cycle,ngx_signal_value(NGX_SHUTDOWN_SIGNAL));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;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");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_cache_manager_processes(cycle, 1);ngx_msleep(100);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_cache_manager_processes(cycle, 0);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));}}}

2. ngx_start_worker_processes 创建工作进程

通过循环创建N个子进程。每个子进程都有独立的内存空间。

子进程的个数由Nginx的配置：ccf->worker_processes决定

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");ngx_memzero(&ch, sizeof(ngx_channel_t));chmand = NGX_CMD_OPEN_CHANNEL;for (i = 0; i < n; i++) {ngx_spawn_process(cycle, ngx_worker_process_cycle,(void *) (intptr_t) i, "worker process", type);ch.pid = ngx_processes[ngx_process_slot].pid;ch.slot = ngx_process_slot;ch.fd = ngx_processes[ngx_process_slot].channel[0];ngx_pass_open_channel(cycle, &ch);}}

3. ngx_spawn_process fork工作进程

ngx_spawn_process方法主要用于fork出各个工作进程。具体主要看fork过程的代码。

        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;    }

4. ngx_worker_process_cycle 子进程的回调函数

ngx_worker_process_cycle为子进程的回调函数，一切子进程的工作从这个方法开始。

Nginx的进程最终也是有事件驱动的，所有这个方法中，最终会调用ngx_process_events_and_timers事件驱动的核心函数。

static void ngx_worker_process_cycle(ngx_cycle_t *cycle, void *data) {ngx_int_t worker = (intptr_t) data;ngx_process = NGX_PROCESS_WORKER;ngx_worker = worker;ngx_worker_process_init(cycle, worker);ngx_setproctitle("worker process");for (;;) {if (ngx_exiting) {ngx_event_cancel_timers();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);if (ngx_terminate) {ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "exiting");ngx_worker_process_exit(cycle);}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_exiting = 1;ngx_close_listening_sockets(cycle);ngx_close_idle_connections(cycle);}}if (ngx_reopen) {ngx_reopen = 0;ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "reopening logs");ngx_reopen_files(cycle, -1);}}}

5. ngx_worker_process_init 工作进程初始化

static void ngx_worker_process_init(ngx_cycle_t *cycle, ngx_int_t worker) {sigset_t set;ngx_int_t n;ngx_uint_t i;ngx_cpuset_t *cpu_affinity;struct rlimit rlmt;ngx_core_conf_t *ccf;ngx_listening_t *ls;if (ngx_set_environment(cycle, NULL) == NULL) {exit(2);}ccf = (ngx_core_conf_t *) ngx_get_conf(cycle->conf_ctx, ngx_core_module);if (worker >= 0 && ccf->priority != 0) {if (setpriority(PRIO_PROCESS, 0, ccf->priority) == -1) {ngx_log_error(NGX_LOG_alert, cycle->log, ngx_errno,"setpriority(%d) failed", ccf->priority);}}if (ccf->rlimit_nofile != NGX_CONF_UNSET) {rlmt.rlim_cur = (rlim_t) ccf->rlimit_nofile;rlmt.rlim_max = (rlim_t) ccf->rlimit_nofile;if (setrlimit(RLIMIT_NOFILE, &rlmt) == -1) {ngx_log_error(NGX_LOG_alert, cycle->log, ngx_errno,"setrlimit(RLIMIT_NOFILE, %i) failed", ccf->rlimit_nofile);}}if (ccf->rlimit_core != NGX_CONF_UNSET) {rlmt.rlim_cur = (rlim_t) ccf->rlimit_core;rlmt.rlim_max = (rlim_t) ccf->rlimit_core;if (setrlimit(RLIMIT_CORE, &rlmt) == -1) {ngx_log_error(NGX_LOG_alert, cycle->log, ngx_errno,"setrlimit(RLIMIT_CORE, %O) failed", ccf->rlimit_core);}}if (geteuid() == 0) {if (setgid(ccf->group) == -1) {ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_errno,"setgid(%d) failed", ccf->group);exit(2);}if (initgroups(ccf->username, ccf->group) == -1) {ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_errno,"initgroups(%s, %d) failed", ccf->username, ccf->group);}if (setuid(ccf->user) == -1) {ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_errno,"setuid(%d) failed", ccf->user);exit(2);}}if (worker >= 0) {cpu_affinity = ngx_get_cpu_affinity(worker);if (cpu_affinity) {ngx_setaffinity(cpu_affinity, cycle->log);}}#if (NGX_HAVE_PR_SET_DUMPABLE)if (prctl(PR_SET_DUMPABLE, 1, 0, 0, 0) == -1) {ngx_log_error(NGX_LOG_alert, cycle->log, ngx_errno,"prctl(PR_SET_DUMPABLE) failed");}#endifif (ccf->working_directory.len) {if (chdir((char *) ccf->working_directory.data) == -1) {ngx_log_error(NGX_LOG_alert, cycle->log, ngx_errno,"chdir(\"%s\") failed", ccf->working_directory.data);exit(2);}}sigemptyset(&set);if (sigprocmask(SIG_SETMASK, &set, NULL) == -1) {ngx_log_error(NGX_LOG_alert, cycle->log, ngx_errno,"sigprocmask() failed");}srandom((ngx_pid << 16) ^ ngx_time());ls = cycle->listening.elts;for (i = 0; i < cycle->listening.nelts; i++) {ls[i].previous = NULL;}for (i = 0; cycle->modules[i]; i++) {if (cycle->modules[i]->init_process) {if (cycle->modules[i]->init_process(cycle) == NGX_ERROR) {exit(2);}}}for (n = 0; n < ngx_last_process; n++) {if (ngx_processes[n].pid == -1) {continue;}if (n == ngx_process_slot) {continue;}if (ngx_processes[n].channel[1] == -1) {continue;}if (close(ngx_processes[n].channel[1]) == -1) {ngx_log_error(NGX_LOG_alert, cycle->log, ngx_errno,"close() channel failed");}}if (close(ngx_processes[ngx_process_slot].channel[0]) == -1) {ngx_log_error(NGX_LOG_alert, cycle->log, ngx_errno,"close() channel failed");}#if 0ngx_last_process = 0;#endifif (ngx_add_channel_event(cycle, ngx_channel, NGX_READ_EVENT,ngx_channel_handler) == NGX_ERROR) {exit(2);}}