Nginx源码分析 - 主流程篇 - 多进程实现

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多进程实现的流程图

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
/**
* Nginx的多进程运行模式
*/
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;

/* 设置能接收到的信号 */
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;
}

/* 保存进程标题 */
title = ngx_pnalloc(cycle->pool, size);
if (title == NULL) {
/* fatal */
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);

/* 获取核心配置 ngx_core_conf_t */
ccf = (ngx_core_conf_t *) ngx_get_conf(cycle->conf_ctx, ngx_core_module);

/* 启动工作进程 - 多进程启动的核心函数 */
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;

/* 主线程循环 */
for (;;) {

/* delay用来设置等待worker推出的时间，master接受了退出信号后，
* 首先发送退出信号给worker，而worker退出需要一些时间*/
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");

/* 等待信号的到来，阻塞函数 */
sigsuspend(&set);

ngx_time_update();

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

/* 收到了SIGCHLD信号，有worker退出(ngx_reap == 1) */
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);
}

/* 中止进程 */
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;
}

/* 退出进程 */
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
.fd) == -1) {
ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_socket_errno,
ngx_close_socket_n " %V failed", &ls
.addr_text);
}
}
cycle->listening.nelts = 0;

continue;
}

/* 收到SIGHUP信号 重新初始化配置 */
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);

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

live = 1;
ngx_signal_worker_processes(cycle,
ngx_signal_value(NGX_SHUTDOWN_SIGNAL));
}

/* 当ngx_noaccepting==1时，会把ngx_restart设为1，重启worker */
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;
}

/* 收到SIGUSR1信号，重新打开log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));
}

/* SIGUSER2，热代码替换 */
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);
}

/* 收到SIGWINCH信号不在接受请求，worker退出，master不退出 */
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
/**
* 创建工作进程
*/
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));

ch.command = NGX_CMD_OPEN_CHANNEL;

/* 循环创建工作进程 默认ccf->worker_processes=8个进程，根据CPU个数决定 */
for (i = 0; i < n; i++) {

/* 打开工作进程 （ngx_worker_process_cycle 回调函数，主要用于处理每个工作线程）*/
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。
/* fork 一个子进程 */
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:
/* 如果pid fork成功，则调用 ngx_worker_process_cycle方法 */
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。
/**
* 子进程 回调函数
* 每个进程的逻辑处理就从这个方法开始
*/
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;

/* 工作进程初始化 */
ngx_worker_process_init(cycle, worker);

ngx_setproctitle("worker process");

/* 进程循环 */
for (;;) {

/* 判断是否是退出的状态，如果退出，则需要清空socket连接句柄 */
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");

/* 事件驱动核心函数 */
ngx_process_events_and_timers(cycle);

if (ngx_terminate) {
ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "exiting");

ngx_worker_process_exit(cycle);
}

/* 如果是退出 */
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);
}
}

/* 如果是重启 */
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

/**
* 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;

/* 配置环境变量 */
if (ngx_set_environment(cycle, NULL) == NULL) {
/* fatal */
exit(2);
}

/* 获取核心配置 */
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);
}
}

/* 设置UID GROUPUID */
if (geteuid() == 0) {
if (setgid(ccf->group) == -1) {
ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_errno,
"setgid(%d) failed", ccf->group);
/* fatal */
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);
/* fatal */
exit(2);
}
}

/* 设置CPU亲和性 */
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)

/* allow coredump after setuid() in Linux 2.4.x */

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");
}

#endif

/* 切换工作目录 */
if (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);
/* fatal */
exit(2);
}
}

sigemptyset(&set);

/* 清除所有信号 */
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());

/*
* disable deleting previous events for the listening sockets because
* in the worker processes there are no events at all at this point
*/
/* 清除sokcet的监听 */
ls = cycle->listening.elts;
for (i = 0; i < cycle->listening.nelts; i++) {
ls[i].previous = NULL;
}

/* 对模块初始化 */
for (i = 0; cycle->modules[i]; i++) {
if (cycle->modules[i]->init_process) {
if (cycle->modules[i]->init_process(cycle) == NGX_ERROR) {
/* fatal */
exit(2);
}
}
}

/**
*将其他进程的channel[1]关闭，自己的channel[0]关闭
*/
for (n = 0; n < ngx_last_process; n++) {

if (ngx_processes
.pid == -1) {
continue;
}

if (n == ngx_process_slot) {
continue;
}

if (ngx_processes
.channel[1] == -1) {
continue;
}

if (close(ngx_processes
.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 0
ngx_last_process = 0;
#endif

/**
* 给ngx_channel注册一个读事件处理函数
*/
if (ngx_add_channel_event(cycle, ngx_channel, NGX_READ_EVENT,
ngx_channel_handler) == NGX_ERROR) {
/* fatal */
exit(2);
}
}
下一章节，我们会讲解Nginx的惊群和进程间的负载均衡处理。