cvs commit: src/share/man/man9 sleep.9

Maxime Henrion mux at
Mon Mar 5 09:32:28 UTC 2007

Greg Lehey wrote:
> grog        2007-03-05 05:59:49 UTC
>   FreeBSD src repository
>   Modified files:
>     share/man/man9       sleep.9 
>   Log:
>   Another typo.
>   Spotted by:             ru
>   Another pointy hat to:  grog
>   Revision  Changes    Path
>   1.58      +1 -1      src/share/man/man9/sleep.9

I've been reading the latest version of this manpage with your
modifications, and still find the information you have added in it
largely misleading and/or wrong.  I'm particularly worried by this
paragraph :

Due to the way it works, the wakeup_one() function requires that only
related threads sleep on a specific chan address.  It is the programmer's
responsibility to choose a unique chan value.  The older wakeup() func-
tion did not require this, though it was never good practice for threads
to share a chan value.  When converting from wakeup() to wakeup_one(),
pay particular attention to ensure that no other threads wait on the same

You're making it look as if sharing the wait channel when using
wakeup_one() is more of a problem than when using wakeup().  This
isn't true; both usages are completely wrong.  What is different
is that when in the wakeup_one() case, the symptoms are likely to
be more apparent and more annoying because chances are that it will
lead to deadlocks pretty quickly.  This does not make sharing wait
channels "more" OK within the context of wakeup().

Also, this particular bit : "The older wakeup() function did not
require this, [...]" looks entirely wrong.  You are somehow mitigating
it by saying that it was never a good practice to share wait channels
afterwards, but this is still untrue.  Sharing wait channels isn't
just "not a good practice", it is entirely incorrect.  As far as I
can tell, the wakeup() function always required separate wait
channels, it's just that the effect of the sharing wasn't necessarily
visible, if every process/thread checks that the condition it was
waiting on is indeed met when it is woken up (and that it goes back
to sleep if it isn't).

I think these changes should be backed out.

As a side note, we really need to migrate from the msleep()/wakeup()
API to using CVs.  It would make those kind of confusions impossible.


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