[TUHS] In V6 exit(): wakeup(&proc)) unnecessary?
Mirian Crzig Lennox
mirian at cosmic.com
Mon Dec 23 05:00:37 AEST 2002
On Sun, 22 Dec 2002 12:15:01 +0100 (MET), Wolfgang Helbig <helbig at 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) 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) 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
>Furthermore, the "goto loop:" at the end of exit() will never be
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.
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