父进程终止后如何杀死所有子进程?

时间:2019-04-13 18:53:25

标签: c linux process posix kill-process

我可以通过父进程杀死一个子进程。但是,如果一个父进程有多个子进程会发生什么?

例如,在下面的代码中,有一个父进程和6个子进程。如何在父进程终止后立即杀死其他六个子进程?

如果运行此代码,则父级将在5秒钟后终止。子进程在又5秒钟(总共10秒钟)后终止。

但是我想在父进程终止后立即杀死6个子进程。因此父级和6个子进程应该在5秒后终止。

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

int main() 
{ 
    for(int i=0;i<6;i++) // loop will run 6 times(there are 6 child processes.) 
    { 
        if(fork() == 0) 
        { 
            printf("Started [son] pid %d from [parent] pid %d\n",getpid(),getppid()); 

            sleep(10); //child waits 10 seconds,then it exitted.

            printf("Exitted [son] pid %d from [parent] pid %d\n",getpid(),getppid()); 

            exit(0); 
        } 
    } 

    //parent
    sleep(5);  //parent will wait 5 seconds than it will exit
    printf("Parent terminated\n");
    exit(0); //parent terminated.(how can I exit the the other 6 child processes too?)

} 

2 个答案:

答案 0 :(得分:2)

在Linux上,您可以使用prctl来请求通过信号通知您的父母去世(跳过错误检查)。

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

#include <sys/prctl.h> //<<<<<<<<
#include <signal.h> //<<<<<<<<

int main() 
{ 
    for(int i=0;i<6;i++) // loop will run 6 times(there are 6 child processes.) 
    { 
        if(fork() == 0) 
        { 
            prctl(PR_SET_PDEATHSIG, SIGTERM); //<<<<<<

            printf("Started [son] pid %d from [parent] pid %d\n",getpid(),getppid()); 

            sleep(2);

            printf("Exitted [son] pid %d from [parent] pid %d\n",getpid(),getppid()); 

            exit(0); 
        } 
    } 

    //parent
    sleep(1);
    printf("Parent terminated\n");
    exit(0);
   //<<< Linux auto-sends the deathsignal to all children

} 

对于不要求父进程死亡的父进程明确终止其子进程的POSIX兼容解决方案,您可以使用async-IO管道。

异步IO依赖于在文件描述符事件上发送的信号。在这种情况下,只要确保自动关闭关闭对管道末端文件的最后引用(跳过错误检查),您就可以收到由内核自动关闭即将死去的进程的文件描述符引起的关闭事件的通知: / p>

#define _GNU_SOURCE
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <unistd.h>

#include <signal.h>
#include <fcntl.h>
#include <sys/ioctl.h>

int main()
{

    int pipes[6][2];
    for(int i=0;i<6;i++) // loop will run 6 times(there are 6 child processes.)
    {
        pipe(pipes[i]); //create a pipe

        if(fork() == 0)
        {
            //get notified on an event on the read-end (we're aiming for the EOF event)
            fcntl(pipes[i][0],F_SETOWN,getpid()); 
            ioctl(pipes[i][0], FIOASYNC, &(int){1});

            for(int j=0; j<=i; j++) close(pipes[j][1]); //close all write-end ends so the refcount is 1 and the parent has the last ref

            printf("Started [son] pid %d from [parent] pid %d\n",getpid(),getppid());

            sleep(2);

            printf("Exitted [son] pid %d from [parent] pid %d\n",getpid(),getppid());

            exit(0);
        }
    }

    //parent
    sleep(1);
    printf("Parent terminated\n");
    exit(0); 
    //<<<this closes all the last write ends of the pipes and so the children will get notified with a signal 
    //the signal is SIGIO by default, whose default disposition is to kill the process (this can be changed by fcntl(fd,F_SETSIG,TheSignal))



}

答案 1 :(得分:2)

这是一个可能更便携的解决方案。

fork(2)系统调用将返回子进程的PID,可以存储PID,然后可以使用kill(2)向子进程发送信号并终止它们。

请注意,SIGKILLSIGTERM信号可能需要父进程的某些特权。如果没有这样的特权,则可以向子进程发送SIGCONT,并在子进程中修改SIGCONT信号处理程序。

!!!警告标志

从信号处理程序中使用exit()是不安全的。我刚刚查看了手册man 7 signal,发现它不是异步安全的。您可以使用_exit_Exitabort

一些伪代码:

#include <stdio.h> 
#include <unistd.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
void* handler(int sig){
    _exit(0);
}
int main() 
{ 
    pid_t children[6];
    for(int i=0;i<6;i++) // loop will run 6 times(there are 6 child processes.) 
    { 
        if((children[i] = fork()) == 0) 
        { 
            signal(SIGCONT,handler);
            printf("Started [son] pid %d from [parent] pid %d\n",getpid(),getppid()); 

            sleep(10); //child waits 10 seconds,then it exitted.

            printf("Exitted [son] pid %d from [parent] pid %d\n",getpid(),getppid()); 

            exit(0); 
        } 
    } 

    //parent
    sleep(5);  //parent will wait 5 seconds than it will exit
    for(int i=0;i<6;i++)
        kill(children[I],SIGCONT);
    printf("Parent terminated\n");
    exit(0); //parent terminated.(how can I exit the the other 6 child processes too?)

}