Question

在GNU libc关于orphaned process groups的手册中，它提到了：

“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. ”

我编写了一个测试程序，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);
}

Answer 1

如果孤立的进程组在孤立时被拦截，则会获得SIGHUP，然后是SIGCONT。

睡眠不够，你需要：

kill(getpid(), SIGSTOP);

除此之外，如果孤立是由setsid()或setprgrp()引起的，POSIX不要求发送SIGHUP和SIGCONT，因为它不是由一个无意识地没有意识到的退出进程引起的工作控制（见http://pubs.opengroup.org/onlinepubs/9699919799/functions/_exit.html）。

但是，使用kill(getpid(), SIGSTOP)代替孩子中的sleep(60)，即使您没有拨打setsid()，您的程序也会获得已停止的孤儿。

#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);
}

在父母去世（5s）后，

应该在孩子身上得到一个SIGHUP。

Answer 2

该文档部分专门讨论了一个进程的控制终端的丢失 - 通常是通过调制解调器挂断或虚拟等效（结束ssh会话等）。（我认为文件中的措词可以在这里改进）。当您在此处使用setsid()时，您会在setsid()返回时放弃对控制终端的访问权限，因此没有控制终端会从此处丢失。

你可以open() tty设备（例如pty slave）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TIOCSCTTY ioctl），然后再次失去它，然后你应该得到SIGHUP信号。

为什么在成为孤立进程组时没有收到SIGHUP信号

2 个答案: