exit from pause()

[jesusitoLinux]

Hi friends! I have a doubt with this code. I have to implement two processes, the child and parent. First the parent will block on pause(), waiting signal SIGUSR1 from the children, and executing a function handler. This is the code

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

void execute()
{
 printf("function execute()\n"); 
}

int main()
{
	int var;
	if(fork()!=0)//parent
	{
	  struct sigaction act_sigexec,old_sigexec;
	  act_sigexec.sa_handler=execute;
	  sigemptyset(&act_sigexec.sa_mask);
	  act_sigexec.sa_flags=0;
	  int ret;
	  sigaction(SIGUSR1, &act_sigexec, &old_sigexec);
	  while(1)
	  {
	    printf("parent waiting for signals\n");
	    pause();
	  }
	}
	else//child
	{
	  while(1)
	  {
	    printf("and this is the child\n");
	    scanf("%d",&var);
	    if(var==1)
	      kill(getppid(),SIGUSR1);
	    else if(var==0)
	    {
	      exit(EXIT_SUCCESS);
	    }
	  }
	}
	return 1;
}

The problem is that when children exits, the parent is still in pause(), and I want pause() to quit when the children exits. How can I achieve this???

Thank you very much!

[hazel]

When the child exits, the parent gets a SIGCHILD from the kernel. You could handle this.

[Rubberman]

1. Set up a signal handler to intercept the SIGUSR1 signals.
2. Use the wait() or waitpid() command to wait on the child death.

You will vector to the signal handler if you get a SIGUSR1 signal, and wait()/waitpid() will return if the child has died before it has issued the SIGUSR1 to you, the parent process.

FWIW, using wait() or waitpid() is preferable to pause() since that will also clean up the child's zombie process in the kernel. In fact, in 30+ years of C/C++ programming, I think I can count the number of times I have used pause() on one thumb...