5

在 GNU libc 关于孤立进程组的手册中，它提到：

“process groups that continue running even after the session leader 
has terminated are marked as orphaned process groups. 

When a process group becomes an orphan, its processes are sent a SIGHUP 
signal. Ordinarily, this causes the processes to terminate. However, 
if a program ignores this signal or establishes a handler for it 
(see Signal Handling), it can continue running as  in the orphan process
 group even after its controlling process terminates; but it still 
cannot access the terminal any more. ”

我写了一个测试程序，但是当进程组成为孤儿时，它的进程没有收到 SIGHUP 信号。我想知道为什么？

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>


static void  
sig_hup(int signo) //**never get called ???**
{
    printf("SIGHUP received, pid = %ld\n", (long)getpid());
}

static void
pr_ids(char *name)
{
    printf("%s: pid = %ld, ppid = %ld, pgrp = %ld, tpgrp = %ld\n",
        name, (long)getpid(), (long)getppid(), (long)getpgrp(),
        (long)tcgetpgrp(STDIN_FILENO));
    fflush(stdout);
}

int
main(void)
{
    char    c;
    pid_t   pid;

    pr_ids("parent");
    pid = fork();
    if (pid > 0) {       // parent 
        sleep(5);
        exit(0);         // parent exit;
    } else {
        pr_ids("child");
        setsid();        //create new session, and "child" becomes the session leader
        pid = fork();
        if(pid>0) {
            sleep(20);
            exit(0);     // "child" exit
                         // so the process group become an orphan process group
        }
        else{
            pr_ids("grandson");
            signal(SIGHUP, sig_hup);    // establish signal handler 
            sleep(60);                  // now becoming orphan process group
            printf("end\n");
        }
    }
    exit(0);
}
4

2 回答 2

3

如果孤立的进程组在它们成为孤立的时候被停止，它们就会被SIGHUP跟踪。SIGCONT

睡眠不够，你需要：

kill(getpid(), SIGSTOP); //or raise(SIGSTOP);

除此之外，如果孤立是由或因为它不是由无辜地不知道作业控制的退出进程引起的，则 POSIX 不需要SIGHUP并且发送（参见http://pubs.opengroup.org/onlinepubs /9699919799/functions/_exit.html )。SIGCONTsetsid()setprgrp()

但是，kill(getpid(), SIGSTOP)即使sleep(60)您不调用setsid().

#define _GNU_SOURCE
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <signal.h>

static void  
sig_hup(int signo) //**never get called ???**
{
    printf("SIGHUP received, pid = %ld\n", (long)getpid());
}

static void
pr_ids(char *name)
{
    printf("%s: pid = %ld, ppid = %ld, pgrp = %ld, tpgrp = %ld\n",
        name, (long)getpid(), (long)getppid(), (long)getpgrp(),
        (long)tcgetpgrp(STDIN_FILENO));
    fflush(stdout);
}

int
main(void)
{
    pid_t   pid;

    pr_ids("parent");
    pid = fork();
    if (pid > 0) {       // parent 
        sleep(5);
        _exit(0);         // parent exit;
    } else {
        pr_ids("child");

        /*setsid();        //create new session, and "child" becomes the session leader*/

        pid = fork();
        if(pid>0) {
            sleep(2);
            exit(0);     // "child" exit
                         // so the process group become an orphan process group
        }
        else{
            pr_ids("grandson");
            signal(SIGHUP, sig_hup);    // establish signal handler 
            kill(getpid(), SIGSTOP);
            printf("end\n");
        }
    }
    exit(0);
}

SIGHUP父母去世后（5s）应该让你在孩子身上得到一个。

于 2016-08-23T19:57:14.137 回答
0

该文档部分专门讨论了一个进程的控制终端的丢失——通常是由于调制解调器挂断或虚拟等价物（结束 ssh 会话等）。（我认为文档中的措辞可以在这里改进）。当你setsid()在这里使用时，你在时间返回时放弃了对控制终端的访问setsid()，所以从那里开始没有控制终端丢失。

你可以open()用一个 tty 设备（比如一个 pty slave）来获得一个控制终端（注意你可能还需要做一些额外的操作——FreeBSD 需要一个TIOCSCTTYioctl），然后再次丢失它，然后你应该得到SIGHUP信号。

于 2013-11-04T02:09:17.047 回答