Date: Fri, 3 Jul 2020 00:36:05 +0530 From: "Kamal R. Prasad" <kamalpr@gmail.com> To: Ian Lepore <ian@freebsd.org> Cc: kamalp@acm.org, freebsd-arm@freebsd.org Subject: Re: cv_wait Message-ID: <CAK=yUGLvZ7uM=pTNrODnTgw6NStT4gHExsTDkrYTP_rQBV1C-A@mail.gmail.com> In-Reply-To: <ef01153a05887b10a443c71cb42aff6180ae7f8f.camel@freebsd.org> References: <CAK=yUGLoM1YWX5yxsboKqaCMr2jKGgtJ0a-CVVsfeEO3SpsYLQ@mail.gmail.com> <ef01153a05887b10a443c71cb42aff6180ae7f8f.camel@freebsd.org>
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but if i am doing cv_wait() for the first time, should someone be
calling cv_signal for it to proceed?
my algo is something like this in my driver:-
function1()
{
mtx_lock(&sc->sc_mtx);
cv_wait(&sc->sc_cv);
mtx_unlock(&sc->sc_mtx);
....
critical section
....
cv_signal(&sc->sc_cv);
}
function2()
{
mtx_lock(&sc->sc_mtx);
cv_wait(&sc->sc_cv);
mtx_unlock(&sc->sc_mtx);
....
critical section
....
cv_signal(&sc->sc_cv);
}
---------------------
i want to protect critical section. The critical section calls a common
piece of code which has some locks. if i put in locks to guard the cs, it
triggers a call to witness().
Update: i saw an implementation wherein they used a callout to periodically
send a cv_signal(). i could do that but the pt of this implementation is
that cs in either of these functions should not be eecuting at the same
time.
thanks
-kamal
On Thu, Jul 2, 2020 at 10:29 PM Ian Lepore <ian@freebsd.org> wrote:
> On Thu, 2020-07-02 at 21:48 +0530, Kamal R. Prasad wrote:
> > hello,
> >
> > i have written a piece of code in a freebsd driver meant for arm. The
> > first
> > cv_wait(&sc->sc_cv, &sc->sc_mtx);
> > keeps waiting indefinitely. If I use cv_timedwait() instead, it
> > returns
> >
> > EWOULDBLOCK
> >
> >
> > does someone know why this is happening?
> >
> >
> > thanks
> >
> > -kamal
> >
>
> That would imply that nothing is ever calling cv_signal(&sc->sc_cv) or
> cv_broadcast(&sc->sc_cv).
>
> -- Ian
>
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