进程模型

        Nginx分为Single和Master两种进程模型。Single模型即为单进程方式工作，具有较差的容错能力，不适合生产之用。Master模型即为一个master进程+N个worker进程的工作方式。

生产环境都是用master-worker模型来工作。

master进程

        我们知道在main函数中完毕了Nginx启动初始化过程，启动初始化过程中的一个重要环节就是解析配置文件。回调各个配置指令的回调函数。因此完毕了各个模块的配置及相互关联。在全部的这些重要及不重要的初始化完毕后。main函数就開始为我们打开进程的“大门”——调用ngx_master_process_cycle(cycle); 在剖析ngx_master_process_cycle(cycle)之前，我们先来看看该函数中用到的7个标志位，如以下的表所看到的：

进程中接收到的信号对Nginx框架的意义：

        另一个标志位会用到：ngx_restart。它不过在master工作流程中作为标志位使用。与信号无关。master进程就是依据这8个标志来决定工作流程的，流程图例如以下：

        下面是对ngx_master_process_cycle()函数源代码的剖析，可參照流程图理解：

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;
/*屏蔽一些列信号*/
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;
}

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);
/*创建子进程，接受请求，完毕响应*/
ngx_start_worker_processes(cycle, ccf->worker_processes,
NGX_PROCESS_RESPAWN);
/*创建有关cache的子进程*/
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: %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;
//设置定时器
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");

/*master进程挂起，等待信号的产生*/
sigsuspend(&set);

ngx_time_update();

ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
"wake up, sigio %i", sigio);
/*ngx_reap若为1。则表示要监控全部子进程*/
if (ngx_reap) {
ngx_reap = 0;
ngx_log_debug0(NGX_LOG_DEBUG_EVENT, cycle->log, 0, "reap children");
/*ngx_reap_children(会遍历ngx_process数组。检查每一个子进程的状态，对于非正常退出的子进程会又一次拉起，
最后。返回一个live标志位，假设全部的子进程都已经正常退出，则live为0。初次之外live为1。*/
live = ngx_reap_children(cycle);
}
/*当live标志为0，而且ngx_terminate或ngx_quit中的一个标志位1时，都将调用ngx_master_process_exit方法退出master进程*/
if (!live && (ngx_terminate || ngx_quit)) {
ngx_master_process_exit(cycle);
}
/*ngx_terminate标志为1，则向全部子进程发送信号TERM。通知子进程强制退出进程*/
if (ngx_terminate) {
if (delay == 0) {
delay = 50;
}

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

sigio = ccf->worker_processes + 2 /* cache processes */;
//强制退出进程
if (delay > 1000) {
ngx_signal_worker_processes(cycle, SIGKILL);
} else {
ngx_signal_worker_processes(cycle,
ngx_signal_value(NGX_TERMINATE_SIGNAL));
}

continue;
}
//优雅地退出服务。向全部子进程发送QUIT信号，通知它们退出进程
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;
}
/*
又一次读取配置文件。Nginx不会让原先的worker等子进程在从新读取配置文件。
它的策略是又一次初始化ngx_cycle_t结构体，用它来读取新的配置文件。再拉起
新的worker进程，销毁就的worker进程。

*/
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");
/*调用ngx_init_cycle方法又一次初始化ngx_cycle_t结构体*/
cycle = ngx_init_cycle(cycle);
if (cycle == NULL) {
cycle = (ngx_cycle_t *) ngx_cycle;
continue;
}

ngx_cycle = cycle;
//又一次读取配置文件
ccf = (ngx_core_conf_t *) ngx_get_conf(cycle->conf_ctx,
ngx_core_module);
//启动worker子进程
ngx_start_worker_processes(cycle, ccf->worker_processes,
NGX_PROCESS_JUST_RESPAWN);
//启动cache_manage子进程
ngx_start_cache_manager_processes(cycle, 1);

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

live = 1;
//向原先的全部子进程发送QUIT信号
ngx_signal_worker_processes(cycle,
ngx_signal_value(NGX_SHUTDOWN_SIGNAL));
}
/*
调用ngx_start_worker_processes拉起worker进程。调用ngx_start_cache_manager_processes
依据缓存模块的请款选择是否启动cache manage进程或者cache loader进程，
同一时候将live置为1。ngx_restart置为0
*/
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;
}
/*又一次打开全部文件*/
if (ngx_reopen) {
/*将ngx_reopen置为0*/
ngx_reopen = 0;
ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "reopening logs");
/*调用ngx_reopen_files方法又一次打开全部文件*/
ngx_reopen_files(cycle, ccf->user);
/*向全部子进程发送USR1信号，要求子进程都又一次打开全部文件*/
ngx_signal_worker_processes(cycle,
ngx_signal_value(NGX_REOPEN_SIGNAL));
}
/*表示须要平滑升级Nginx*/
if (ngx_change_binary) {
/*将ngx_change_binary标志置为0*/
ngx_change_binary = 0;
ngx_log_error(NGX_LOG_NOTICE, cycle->log, 0, "changing binary");
/*调用ngx_exec_new_binary方法用新的子进程启动新版本号的Nginx程序*/
ngx_new_binary = ngx_exec_new_binary(cycle, ngx_argv);
}
/*向全部子进程发送QUIT信号，要求他们优雅关闭服务*/
if (ngx_noaccept) {
/*将ngx_noaccept置为0*/
ngx_noaccept = 0;
/*将ngx_noaccepting置为1，表示正在停止接受新的连接*/
ngx_noaccepting = 1;
/*向全部子进程发送QUIT信号*/
ngx_signal_worker_processes(cycle,
ngx_signal_value(NGX_SHUTDOWN_SIGNAL));
}
}
}

 转载注明出处，谢谢~~