进程间通讯(四).非亲缘进程间交互信号
前言
UNIX/Linux 是多任务的操作系统，通过多个进程分别处理不同事务来实现，如果多个进程要进行协同工作或者争用同一个资源时，互相之间的通讯就很有必要了
进程间通信，Inter process communication，简称 IPC，在 UNIX/Linux 下主要有以下几种方式:
- 无名管道 ( pipe )
- 有名管道 ( fifo )
- 信号 ( signal )
- 信号量 ( semaphore )
- 消息队列 ( message queues )
- 共享内存 ( shared memory )
- 套接字 ( socket )
这里分享一下我在学习进程通讯过程中的笔记和心得
Tip: 前面分别演示了 FIFO 和 signal 的功能，FIFO 可以实现非亲缘进程间的通讯，signal可以实现父子进程间发送信号，将两者结合可以实现非亲缘进程间交互信号
概要
代码示例
要求
有A、B两个进程（无亲缘），实现如下功能：
- 1.A进程运行开始3秒后，向B进程发送一个40号信号
- 2.B收到信号后，打印“A，I have received your signal,now I will kill you!”
- 3.然后B向A发送SIGKILL信号使A进程退出。
要求：用signal做
提示：先可以用fifo互相告知对方的pid
代码示例
signalB.c
#include <stdio.h>
#include <signal.h> //signal,kill 等相关函数的原型声明
#include <unistd.h> //getpid,unlink,access,read,write,pause,close 等相关函数的原型声明
#include <sys/stat.h> //mkfifo 等相关函数的原型声明
#include <errno.h> //EEXIST,errno 等相关函数的原型声明
#include <fcntl.h> //open,O_RDONLY,O_WRONLY 等相关函数的原型声明和宏定义
void trigger(int signum) //定义一个触发函数，在收到信号后被调用
{
printf("B:A, I have received your signal , now I will kill you!, the signal is %d\n",signum); //打印一句话，并且将收到的信号打印出来
}
int main()
{
pid_t pid=getpid(),opid=0;
char *rfifo="/tmp/abfifo";
char *wfifo="/tmp/bafifo";
int rfd=0,wfd=0,res=-1,sig=9; //进行各种变量的初始化
unlink(rfifo);
unlink(wfifo); //删除掉现存的管道文件
if(-1 == access(rfifo,F_OK)) //如果rfifo不存在，则创建
{
if(0 > (mkfifo(rfifo,0600)) && (EEXIST != errno)) //如果创建rfifo失败，并且出错不是文件已经存在，则提示并返回
{
printf("cannot create fifo file %s\n",rfifo);
return res;
}
}
if(-1 == access(wfifo,F_OK)) //同样创建wfifo
{
if(0 > (mkfifo(wfifo,0600)) && (EEXIST != errno))
{
printf("cannot create fifo file %s\n",wfifo);
return res;
}
}
if(-1 == (rfd = open(rfifo,O_RDONLY))) //打开rfifo
{
printf("cannot open fifo file:%s\n",rfifo);
return res;
}
if(sizeof(pid_t) != read(rfd,&opid,sizeof(pid_t))) //从rfifo中读取pid_t型数值，并且存放到opid中
{
printf("read error on %s",rfifo);
return res;
}
if(-1 == (wfd = open(wfifo,O_WRONLY))) //打开wfifo
{
printf("cannot open fifo file:%s\n",wfifo);
return res;
}
if(sizeof(pid_t) != write(wfd,&pid,sizeof(pid_t))) //将自己的pid写到wfifo中
{
printf("write error on : %s\n",wfifo);
return res;
}
printf("B:my pid is %d, other process pid is %d\n",pid,opid); //打印出自己的pid和从管道中获取的另一个进程的pid
signal(40,trigger); //收到40号信号就进行trigger函数处理
pause(); //在收到信号之前，一直处于阻塞状态
if(0 == kill(opid,sig)) //给另一个进程发送信号
{
printf("B:sent %d signal to %d\n",sig,opid);
}
else
{
perror("B:kill");
}
close(wfd);
close(rfd); //进行收尾清理
res=0;
return res;
}signalA.c
#include <stdio.h>
#include <signal.h> //signal,kill 等相关函数的原型声明
#include <unistd.h> //getpid,write,read,sleep,close 等相关函数的原型声明
#include <fcntl.h> //open,O_RDONLY,O_WRONLY 等相关函数的原型声明和宏定义
int main()
{
pid_t pid=getpid(),opid=0;
char *rfifo="/tmp/bafifo";
char *wfifo="/tmp/abfifo";
int rfd=0,wfd=0,res=-1,sig=40; //进行各种变量的初始化
if(-1 == (wfd = open(wfifo,O_WRONLY))) //打开wfifo
{
printf("cannot open fifo file:%s\n",wfifo);
return res;
}
if(sizeof(pid_t) != write(wfd,&pid,sizeof(pid_t))) //将自己的pid写到wfifo中去
{
printf("write error on : %s\n",wfifo);
return res;
}
if(-1 == (rfd = open(rfifo,O_RDONLY))) //打开rfifo
{
printf("cannot open fifo file:%s\n",rfifo);
return res;
}
if(sizeof(pid_t) != read(rfd,&opid,sizeof(pid_t))) //从rfifo中获取pid_t类型的数据并且存储到opid中
{
printf("read error on %s",rfifo);
return res;
}
printf("A:my pid is %d, other process pid is %d\n",pid,opid); //将自己的和另一个进程的pid进行输出
sleep(3); //沉睡3秒
printf("A:I am ready to sent sig %d to process which pid is %d\n",sig,opid);
if(0 == kill(opid,sig)) //发送指定信号给另一个进程
{
printf("A:sent %d signal to %d\n",sig,opid);
}
else
{
perror("A:kill");
return res;
}
while(1) //一个死循环，用来查看被信号终结的效果
{
printf("A:this is A process with pid %d, opid is %d\n",pid,opid);
}
close(wfd);
close(rfd); //进行收尾清理
res=0;
return res;
}编译执行
emacs@ubuntu:~/c$ alias gtc
alias gtc='gcc -Wall -g -o'
emacs@ubuntu:~/c$ gtc signalA.x signalA.c
emacs@ubuntu:~/c$ gtc signalB.x signalB.c
emacs@ubuntu:~/c$ 先执行signalB.x，因为等待管道输入，所以会在终端挂起
emacs@ubuntu:~/c$ ./signalB.x 执行signalA.x，会等3秒后立即返回
emacs@ubuntu:~/c$ ./signalA.x
A:my pid is 19428, other process pid is 19427
A:I am ready to sent sig 40 to process which pid is 19427
A:sent 40 signal to 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
A:this is A process with pid 19428, opid is 19427
已杀死
emacs@ubuntu:~/c$这时signalB.x 也有返回了
emacs@ubuntu:~/c$ ./signalB.x
B:my pid is 19427, other process pid is 19428
B:A, I have received your signal , now I will kill you!, the signal is 40
B:sent 9 signal to 19428
emacs@ubuntu:~/c$ 编译执行过程中没有报错，从结果来看，符合预期
unlink
在 unistd.h 中有关于 unlink 的原型声明
/* Remove the link NAME. */
extern int unlink (__const char *__name) __THROW __nonnull ((1));它所起的作用就是删除文件
总结
以下函数可以进行有名管道的创建和信号的控制
- signal
- kill
- pause
- mkfifo
通过各方面资料弄懂其参数的意义和返回值的类型，是熟练掌握的基础
原文地址
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本文系转载，前往查看
如有侵权，请联系 cloudcommunity@tencent.com 删除。
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