本文分析了Nginx中的信号处理机制，包括信号初始化、处理函数及关键变量的作用。通过对ngx_init_signals()函数和signals数组的解析，揭示了Nginx如何通过不同信号控制其启动、停止和升级过程。
- 序
- ngx_init_signals()函数
- ngx_signal_t结构
- signals数组
- sigaction结构
- ngx_signal_handler()函数
- ngx_master_process_cycle()数
- 小结
1序
本文主要分析nginx信号初始化及其处理，信号处理用于master进程的接收reload，stop等操作。
2.1 ngx_init_signals()函数
ngx_int_t
ngx_init_signals(ngx_log_t *log)
{
ngx_signal_t *sig;
struct sigaction sa;
for (sig = signals; sig->signo != 0; sig++) {
ngx_memzero(&sa, sizeof(struct sigaction));
sa.sa_handler = sig->handler;
sigemptyset(&sa.sa_mask);//清空此信号集
if (sigaction(sig->signo, &sa, NULL) == -1) {//设置相关singl的action
//signaction，则可以设置比较多的消息。尤其是在信号处理函数过程中接受信号，进行何种处理
//替代signal 来设计的较稳定的信号处理
#if (NGX_VALGRIND)
ngx_log_error(NGX_LOG_ALERT, log, ngx_errno,
"sigaction(%s) failed, ignored", sig->signame);
#else
ngx_log_error(NGX_LOG_EMERG, log, ngx_errno,
"sigaction(%s) failed", sig->signame);
return NGX_ERROR;
#endif
}
}
return NGX_OK;
}2.2 ngx_signal_t结构
//Nginx服务器的启动、停止和升级都是通过信号控制的
typedef struct {
int signo;//信号的编号
char *signame;//信号的字符串表现形式，如"SIGIO"。
char *name;//信号的名称，如"stop"。
void (*handler)(int signo);//信号处理函数。
} ngx_signal_t;当收到信号会先调用handler函数。
2.3 signals数组
ngx_signal_t signals[] = {
{ ngx_signal_value(NGX_RECONFIGURE_SIGNAL),//RECONFIGURE信号，重新读取配置信息
"SIG" ngx_value(NGX_RECONFIGURE_SIGNAL),//SIGHUP信号
"reload",
ngx_signal_handler },
{ ngx_signal_value(NGX_REOPEN_SIGNAL),
"SIG" ngx_value(NGX_REOPEN_SIGNAL),//SIGHUP信号
"reopen",
ngx_signal_handler },
{ ngx_signal_value(NGX_NOACCEPT_SIGNAL),//NOACCEPT信号，工作进程不接受事件
"SIG" ngx_value(NGX_NOACCEPT_SIGNAL),
"",
ngx_signal_handler },
{ ngx_signal_value(NGX_TERMINATE_SIGNAL),//TERMINATE信号，工作进程终止
"SIG" ngx_value(NGX_TERMINATE_SIGNAL),
"stop",
ngx_signal_handler },
{ ngx_signal_value(NGX_SHUTDOWN_SIGNAL),
"SIG" ngx_value(NGX_SHUTDOWN_SIGNAL),//SHUTDOWN信号，结束网络通信
"quit",
ngx_signal_handler },
{ ngx_signal_value(NGX_CHANGEBIN_SIGNAL),//CHANGEBIN信号，热升级Nginx运行程序
"SIG" ngx_value(NGX_CHANGEBIN_SIGNAL),
"",
ngx_signal_handler },
//以下是常见的系统信号
{ SIGALRM, "SIGALRM", "", ngx_signal_handler },
{ SIGINT, "SIGINT", "", ngx_signal_handler },//来自键盘的中断信号 ( ctrl + c )
{ SIGIO, "SIGIO", "", ngx_signal_handler },//表示 Io 有数据可供读取
{ SIGCHLD, "SIGCHLD", "", ngx_signal_handler },//标识子进程停止或结束的信号
{ SIGSYS, "SIGSYS, SIG_IGN", "", SIG_IGN },
//在linux下写socket的程序的时候，如果尝试send到一个disconnected socket上，就会让底层抛出一个SIGPIPE信号。
//这个信号的缺省处理方法是退出进程
{ SIGPIPE, "SIGPIPE, SIG_IGN", "", SIG_IGN },//无效系统调用
{ 0, NULL, "", NULL }
};3. ngx_signal_handler()函数
主要是赋值ngx_quit 、ngx_terminate 、ngx_noaccept 等变量在ngx_master_process_cycle()中做判断
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):
if (ngx_daemonized) {
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:
ngx_sigalrm = 1;
break;
case SIGIO:
ngx_sigio = 1;
break;
case SIGCHLD:
ngx_reap = 1;
break;
}
break;
case NGX_PROCESS_WORKER:
case NGX_PROCESS_HELPER:4. ngx_master_process_cycle()数
sigprocmask(SIG_BLOCK, &set, NULL) //将SIGINT信号阻塞
sigsuspend()//等待信号，知道有信号才苏醒，在ngx_signal_handler响应处理之后
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));
//将SIGINT信号阻塞，同时保存当前信号集
//记住是屏蔽，不是消除，就是来了信号，如果当前是block，则先不传递给当前进程，但是一旦unblock，则信号会重新到达
if (sigprocmask(SIG_BLOCK, &set, NULL) == -1) {
ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_errno,
"sigprocmask() failed");
}
sigemptyset(&set);
........
........
for ( ;; ) {
sigsuspend(&set); //用于在接收到某个信号之前，临时用mask替换进程的信号掩码，并暂停进程执行，直到收到信号为止
ngx_time_update();
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;
}
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;
}5. 小结
再接再厉
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