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Old 09-28-2004, 07:52 AM   #1
coolfrog
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Registered: Sep 2004
Location: India
Distribution: Slackware 10.0
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Killing child process


Hi,
i am currently working on the Diner Philosophers problem. I have this code :
Code:
while(ctr < 5)
	{
		switch(pid=fork())
		{
			case 0:	p.pid = ctr;
				for(i=0;i<iteration;i++)
				{
					cout << "\n" << p.pid << ": Thinking.....";
					sleep(rand());	//	THINKING
					cout << "\n" << p.pid << ": Acquiring right chopstick.....";
					lock(p.pid);	//	LOCK RIGHT CHOPSTICK
					cout << "\n" << p.pid << ": Acquiring left chopstick.....";
					lock((p.pid+1)%5);	//	LOCK LEFT CHOPSTICK
					cout << "\n" << p.pid << ": Eating.....";
					sleep(rand());
					cout << "\n" << p.pid << ": Releasing chopsticks.....";
					unlock(p.pid);	//	LOCK RIGHT CHOPSTICK
					unlock((p.pid+1)%5);	//	LOCK LEFT CHOPSTICK				
				}
				cout << "\nProcess " << p.pid << " exiting....";
				exit(0);
				break;
			case -1: cout << "\nError";
				break;
			default: ctr++;
				continue;
		}
		break;
	}
Now after fork the child process does enter case 0 but does not enter for loop. Also after the entire program terminates and when i execute the command 'ps' i still have 5 a.out processes running. How do i kill the processes permanently through C/C++ code ? What about the for loop problem ?
 
Old 09-28-2004, 11:11 AM   #2
koyi
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Registered: Jul 2003
Location: Osaka, Japan
Distribution: Arch, Ubuntu
Posts: 421

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As far as I know, there are two ways to prevent the child process from becoming a zombie process.

1. Call wait() from the parent process.
2. After the first fork(), fork() again and kill the child process immediately thus handing the grand-child process to the init process. I am not sure whether you should do a wait() in the parent process in this case. So please do experiment yourself.

Search for "kill zombie process" may help you understand why those child processes exist.
 
Old 09-28-2004, 12:48 PM   #3
trickykid
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Moved: Seems more suitable in the Programming forum.
 
Old 09-28-2004, 02:58 PM   #4
aluser
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Registered: Mar 2004
Location: Massachusetts
Distribution: Debian
Posts: 557

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sleep() takes its time in seconds, and rand returns a number between 0 and RAND_MAX. On my system, RAND_MAX is over 200 million, so your program would sleep, on average, around 3 years at the first "THINKING" comment. That sounds wrong.

To kill a process, see the kill() syscall's man page.
 
  


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