unix 的信号signal常用于进程管理.

比如管理员或者操作系统通过向master进程实现重启和关闭服务．

master进程通过向worker进程发信号管理worker进程．

通常会在进程自定义信号处理函数,处理相关的逻辑.

自定义信号处理函数,从使用者的角度看,很简单,有点像快捷键的定制.

FPM 信号处理有以下几个特点:

master进程,不是直接处理信号,而是通过socketpair创建一个管道,把信号转换一个字符,写到管道里,master进程事件处理无限循环,读取到这个字符时,调用对应的函数.

socketpair,通常管道不同进程通信,而这里确是在同一个进程内部通信,左手交右手,感觉多此一举.

这样做的好处是: 避免信号处理函数与事件处理逻辑同时运行的情况.

注意worker 进程没有用到这个socketpair管道.

worker 进程的信号处理常见的方式,直接绑定处理函数.

处理过程: sig_soft_quit -> fpm_php_soft_quit -> fcgi_set_in_shutdown

fcgi_set_in_shutdown 函数很简单 就是设置in_shutdown这个全局的worker进程开关

worker进程无限循环时,每次都会检查这个开关, in_shutdown=1 时,跳出循环,优雅退出.

源码注释说明:

//fpm_signals.c

#include "fpm_config.h"

...

//整数数组,存放socketpair创建的管道两端文件句柄

static int sp[2];

...

//worker进程信号处理函数

static void sig_soft_quit(int signo) /* {{{ */

{

int saved_errno = errno;

/* closing fastcgi listening socket will force fcgi_accept() exit immediately */

close(0);

if (0 > socket(AF_UNIX, SOCK_STREAM, 0)) {

zlog(ZLOG_WARNING, "failed to create a new socket");

}

fpm_php_soft_quit();

errno = saved_errno;

}

//master进程信号处理函数

static void sig_handler(int signo) /* {{{ */

{

//C99 的数组初始化语法

//信号整数和字符的对应关系.

static const char sig_chars[NSIG + 1] = {

[SIGTERM] = 'T',

[SIGINT] = 'I',

[SIGUSR1] = '1',

[SIGUSR2] = '2',

[SIGQUIT] = 'Q',

[SIGCHLD] = 'C'

};

char s;

int saved_errno;

if (fpm_globals.parent_pid != getpid()) {

return;

}

saved_errno = errno;

s = sig_chars[signo];

//信号对应的字符写到管道

write(sp[1], &s, sizeof(s));

errno = saved_errno;

}

int fpm_signals_init_main() /* {{{ */

{

struct sigaction act;

//创建socketpair管道,管道两端的文件句柄fd 放在数组sp里

if (0 > socketpair(AF_UNIX, SOCK_STREAM, 0, sp)) {

zlog(ZLOG_SYSERROR, "failed to init signals: socketpair()");

return -1;

}

if (0 > fd_set_blocked(sp[0], 0) || 0 > fd_set_blocked(sp[1], 0)) {

zlog(ZLOG_SYSERROR, "failed to init signals: fd_set_blocked()");

return -1;

}

if (0 > fcntl(sp[0], F_SETFD, FD_CLOEXEC) || 0 > fcntl(sp[1], F_SETFD, FD_CLOEXEC)) {

zlog(ZLOG_SYSERROR, "falied to init signals: fcntl(F_SETFD, FD_CLOEXEC)");

return -1;

}

memset(&act, 0, sizeof(act));

act.sa_handler = sig_handler; //所有信号使用同一个处理函数

sigfillset(&act.sa_mask);

if (0 > sigaction(SIGTERM, &act, 0) ||

0 > sigaction(SIGINT, &act, 0) ||

0 > sigaction(SIGUSR1, &act, 0) ||

0 > sigaction(SIGUSR2, &act, 0) ||

0 > sigaction(SIGCHLD, &act, 0) ||

0 > sigaction(SIGQUIT, &act, 0)) {

zlog(ZLOG_SYSERROR, "failed to init signals: sigaction()");

return -1;

}

return 0;

}

int fpm_signals_init_child()

{

struct sigaction act, act_dfl;

memset(&act, 0, sizeof(act));

memset(&act_dfl, 0, sizeof(act_dfl));

act.sa_handler = &sig_soft_quit;

act.sa_flags |= SA_RESTART;

act_dfl.sa_handler = SIG_DFL; //系统默认动作

//worker 进程不使用socketpair创建的管道

close(sp[0]);

close(sp[1]);

if (0 > sigaction(SIGTERM, &act_dfl, 0) ||

0 > sigaction(SIGINT, &act_dfl, 0) ||

0 > sigaction(SIGUSR1, &act_dfl, 0) ||

0 > sigaction(SIGUSR2, &act_dfl, 0) ||

0 > sigaction(SIGCHLD, &act_dfl, 0) ||

0 > sigaction(SIGQUIT, &act, 0)) {

zlog(ZLOG_SYSERROR, "failed to init child signals: sigaction()");

return -1;

}

return 0;

}

int fpm_signals_get_fd()

{

return sp[0];

}

master 进程的信号被写到了管道,管道另一端的处理:

//fpm_events.c

static void fpm_got_signal(struct fpm_event_s *ev, short which, void *arg)

{

char c;

int res, ret;

int fd = ev->fd;

do {

do {

res = read(fd, &c, 1);

} while (res == -1 && errno == EINTR);

if (res <= 0) {

if (res < 0 && errno != EAGAIN && errno != EWOULDBLOCK) {

zlog(ZLOG_SYSERROR, "unable to read from the signal pipe");

}

return;

}

//依据读取到的字符做处理

switch (c) {

...

case 'Q' : /* SIGQUIT */

zlog(ZLOG_DEBUG, "received SIGQUIT");

zlog(ZLOG_NOTICE, "Finishing ...");

fpm_pctl(FPM_PCTL_STATE_FINISHING, FPM_PCTL_ACTION_SET);

break;

case '1' : /* SIGUSR1 */

zlog(ZLOG_DEBUG, "received SIGUSR1");

if (0 == fpm_stdio_open_error_log(1)) {

zlog(ZLOG_NOTICE, "error log file re-opened");

} else {

zlog(ZLOG_ERROR, "unable to re-opened error log file");

}

ret = fpm_log_open(1);

if (ret == 0) {

zlog(ZLOG_NOTICE, "access log file re-opened");

} else if (ret == -1) {

zlog(ZLOG_ERROR, "unable to re-opened access log file");

}

/* else no access log are set */

break;

case '2' : /* SIGUSR2 */

zlog(ZLOG_DEBUG, "received SIGUSR2");

zlog(ZLOG_NOTICE, "Reloading in progress ...");

fpm_pctl(FPM_PCTL_STATE_RELOADING, FPM_PCTL_ACTION_SET);

break;

}

if (fpm_globals.is_child) {

break;

}

} while (1);

return;

}