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From: rhys@batserver.cs.uq.oz.au (Rhys Weatherley)
Newsgroups: comp.unix.questions
Subject: Re: How do you handle while(1) fork(); ?
Message-ID: <4261@uqcspe.cs.uq.oz.au>
Date: 12 Jul 90 10:09:55 GMT
References: <841@massey.ac.nz> <1990Jul11.115612.2155@aucs.uucp>
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Reply-To: rhys@batserver.cs.uq.oz.au
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peter@aucs.uucp (Peter Steele) writes:

>ARaman@massey.ac.nz (A.V. Raman) writes:

>>Is there any way to kill all instances of a process that has the
>>following piece of code in it without having to bring the system down?

>>   while (1)
>>      fork();

>>Any help (by email) would be appreciated.

>I think a summary of responses to this question would be appreciated.
>We've had students do this on many occasions on our Sun.

I would also be interested in a summary, but how about this one:

	while (!fork ())
	  {
	    /* some non-important code */
	  }
	/* some "clean-up" code */
	exit (0);

This will create a round-robin of processes, where each process spawns
a child, and then dies (fork() returns 0 in the child process).  Extremely 
difficult to kill these ones, because by the time you have a process-id 
to kill, that process doesn't exist usually anymore!  This is an 
over-simplification of the code to produce this effect, but both examples 
show the danger of using fork(), when you don't really know what you're doing!  

Personally I prefer the idea of having some sort of library 'spawn' function 
which takes a program name and arguments (similar to exec, without overwriting
the current process), and takes care of all the details for you when you want 
to start up a new program as a child process, allowing the experts to deal 
with fork() and its friends.  (This has no doubt been covered before :-).

Rhys.

+===============================+==============================+
||  Rhys Weatherley             |  University of Queensland,  ||
||  rhys@batserver.cs.uq.oz.au  |  Australia.  G'day!!        ||
+===============================+==============================+