22 Dec
2002
22 Dec
'02
5:15 p.m.
Hi,
encouraged by the profound answers I thankfully recieved to my previous
question about the Unix V6 kernel, here is another one:
When a process terminates (in sys1.c/exit()), it explicitly wakes up
the init process. In light of the fact, that every process has a parent,
this extra wakeup(&proc[1]) seems unnecessary. Furthermore, the "goto
loop:"
at the end of exit() will never be executed.
So is this just defensive programming, or did I miss something?
Greetings,
Wolfgang Helbig
23 Dec
23 Dec
1 a.m.
On Sun, 22 Dec 2002 12:15:01 +0100 (MET), Wolfgang Helbig
<helbig(a)Informatik.BA-Stuttgart.DE> wrote:
When a process terminates (in sys1.c/exit()), it explicitly wakes up
the init process. In light of the fact, that every process has a parent,
this extra wakeup(&proc[1]) seems unnecessary.
I believe this is meant to handle the case where a process exits
without having called wait() on its children.
Imagine two processes, A and B, where A is B's parent and A's parent
is some process other than init. B calls exit(), becomes a zombie,
and awakens A. Some time later, A calls exit() without ever having
called wait(). This will cause B to become a child of init, and as B
is a zombie, init should awaken so that B can die. However, A might
have any number of zombie children, and it would be redundant to call
wakeup(&proc[1]) for each one. Therefore, the wakeup call to init is
done up front, whether it is needed or not. This does result in some
unnecessary wakeup calls but on the whole it seems a good tradeoff for
code simplicity.
Furthermore, the "goto loop:" at the end of
exit() will never be
executed.
This seems to be correct. I can't think of any normal sequence of
events which could result in an exiting process having no parent in
the process table.
--Mirian
8035
days inactive
8035
days old
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Wolfgang Helbig