From: helbig@Informatik.BA-Stuttgart.DE (Wolfgang Helbig)
Subject: [TUHS] In V6 exit(): wakeup(&proc[1])) unnecessary?
Date: Mon, 23 Dec 2002 00:01:55 +0100 (MET) [thread overview]
Message-ID: <200212230104.gBN14iw00526@bsd.korb> (raw)
>>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.
Oh, I see! So the condition to wakeup init would be
"Do I have any zombie children"?
The code as it is is simpler. But harder to understand.
Thank you very much for your help!
Greetings
Wolfgang Helbig
next reply other threads:[~2002-12-22 23:01 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-12-22 23:01 Wolfgang Helbig [this message]
-- strict thread matches above, loose matches on Subject: below --
2002-12-22 11:15 Wolfgang Helbig
2002-12-22 19:00 ` Mirian Crzig Lennox
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