linux多进程通讯---信号底层API sigaction sigqueue

sigaction 函数原型

int sigaction(int signum, const struct sigaction *act,struct sigaction *oldact);

sigaction 函数功能

•函数功能：给信号设置新的注册函数act，同时保留原有的信号处理函数在oldact
–执行某些信号时屏蔽某些信号，直接给sa_mask赋值即可
–处理带参数的信号
–一次注册，长期有效

struct sigaction 
{ 
	void (*sa_handler)(int); 
	void (*sa_sigaction)(int, siginfo_t *, void *); 
	sigset_t sa_mask; 
	int sa_flags; 
	void (*sa_restorer)(void); 
};

sigqueue 函数原型

int sigqueue (pid_t pid, int sig, const union sigval value);

sigqueue 函数功能

–用法与kill类似
–与kill不同之处：kill可以将 pid 设置为指定负值，向整个进程发送信号
–可以给指定进程传递一个int型数据
–sigaction 和 sigqueue 是一对 CP

一些经验

•一旦给信号安装了handler，它就一直有效
•信号的handler存在并发访问、可重入问题
•在信号的handler运行期间，会阻塞掉当前本身该信号
•在handler运行期间，当前信号的多次提交可能被丢弃，只保留一次
•除了本身信号是被阻塞的，可以通过设置，阻塞设定的一些信号
•signal是标准C定义的函数，而sigaction是POSIX接口函数
•Signal是对sigaction的封装
•不同的架构、操作系统对信号的value、default action 可能不一样
•特殊的两个信号：SIGKILL和SIGSTOP
–不能被忽略
–不能安装signal handler、不能被捕捉
–不能被阻塞

示例

signal

#include <signal.h>
#include <unistd.h>
#include <stdio.h>


void handler (int signo)
{
    int i,j;
	switch (signo)
	{
		case SIGHUP:
			printf ("get a SIGHUP signal: %d\n", signo);
			break;
		case SIGINT:
			printf ("get a SIGINT signal: %d\n", signo);
			break;
		case SIGQUIT:
			printf ("get a SIGQUIT signal: %d\n", signo);
			break;
        case SIGUSR1:
            printf ("get a SIGUSR1 signal: %d\n", signo);
            break;
        default:
            printf ("unknow signal\n");
	}
    for (i = 0; i < 10000; i++)  
    {
        for (j = 0; j < 1000; j++)
            ;
    }
    printf ("handler exit with signo: %d\n", signo);
}


int main (void)
{
	signal (SIGHUP, handler);
	signal (SIGINT, handler);
	signal (SIGQUIT, handler);
	signal (SIGUSR1, handler);

	while (1);
	return 0;
}
//test 1:
// run:  kill -HUP  22380
// run:  kill -HUP  22380
// run:  kill -HUP  22380
// run:  kill -HUP  22380
// run:  kill -HUP  22380
//test 2:
// run:  kill -HUP  22380
// run:  kill -INT  22380
// run:  kill -QUIT  22380
// run:  kill -USR1  22380
// run:  kill -HUP  22380

sigaction 和 sigqueue CP交互

sigaction

#include <unistd.h>
#include <signal.h>
#include <stdio.h>

void signal_handler (int signum)
{
    printf ("signal_handler\n");
    switch (signum)
    {
        case SIGHUP:
            printf ("get signal: SIGHUP\n");
            sleep (20);
            break;
        case SIGINT:
            printf ("get signal: SIGINT\n");
            break;
        case SIGQUIT:
            printf ("get signal: SIGQUIT\n");
            break;
        case SIGUSR1:
            printf ("get signal: SIGUSR1\n");
            break;
        default:
            printf ("undefined signal\n");
    }
}
void signal_sigaction (int signum, siginfo_t *parm, void *parm2)
{
    printf ("signal_sigaction\n");
    switch (signum)
    {
        case SIGHUP:
            printf ("get signal: SIGHUP\n");
            break;
        case SIGINT:
            printf ("get signal: SIGINT\n");
            break;
        case SIGQUIT:
            printf ("get signal: SIGQUIT\n");
            break;
        case SIGUSR1:
            printf ("get signal: SIGUSR1\n");
    }
    printf ("received data: %d\n", parm->si_value);
    printf ("sending signal process pid : %d\n", parm->si_pid);
}


int main (void)
{
	struct sigaction act, old_act;
    act.sa_sigaction = signal_sigaction;
	act.sa_handler = signal_handler;
	sigemptyset (&act.sa_mask);
	sigaddset (&act.sa_mask, SIGUSR1);
    act.sa_flags = 0;
        //sa_flags must be set,or it will cause core dump
        //set 0 may cause signal losing
        //act.sa_flags = SA_RESETHAND | SA_NODEFER;
        //SA_RESETHAND: restore signal action to DEF
        //SA_SIGINFO: use sa_sigaction as signal handler
        //SA_NODEFER: umask sa_mask

	sigaction (SIGHUP, &act, &old_act);
//	sigaction (SIGINT, &act, &old_act);
//	sigaction (SIGQUIT, &act, &old_act);
//	sigaction (SIGUSR1, &act, &old_act);
    while (1);
	return 0;
}

sigqueue

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>

int main (int argc, char *argv[])
{
    union sigval val;
    val.sival_int = 10;
    pid_t pid = atoi (argv[1]);
    if (sigqueue (pid, SIGHUP, val) == -1)
    {
        perror ("sigqueue");
        exit (EXIT_FAILURE);
    }
    printf ("current pid:%d\n", getpid());
    return 0;
}