Date: Mon, 12 Mar 2007 21:17:52 +0100 From: "Attilio Rao" <attilio@freebsd.org> To: "Pawel Jakub Dawidek" <pjd@freebsd.org> Cc: cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org, John Baldwin <jhb@freebsd.org> Subject: Re: cvs commit: src/share/man/man9 Makefile condvar.9 lock.9 mi_switch.9 mtx_pool.9 mutex.9 rwlock.9 sleep.9 sleepqueue.9 sx.9 thread_exit.9 src/sys/kern kern_synch.c src/sys/sys mutex.h rwlock.h sleepqueue.h sx.h systm.h Message-ID: <3bbf2fe10703121317h2fc8d639qfd47def80f5cbe91@mail.gmail.com> In-Reply-To: <20070312200345.GB5688@garage.freebsd.pl> References: <200703092241.l29Mf2Ds062856@repoman.freebsd.org> <200703121116.24667.jhb@freebsd.org> <20070312185638.GA5688@garage.freebsd.pl> <200703121535.22140.jhb@freebsd.org> <20070312200345.GB5688@garage.freebsd.pl>
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2007/3/12, Pawel Jakub Dawidek <pjd@freebsd.org>:
> On Mon, Mar 12, 2007 at 03:35:21PM -0400, John Baldwin wrote:
> > On Monday 12 March 2007 14:56, Pawel Jakub Dawidek wrote:
> > > On Mon, Mar 12, 2007 at 11:16:23AM -0400, John Baldwin wrote:
> > > > On Saturday 10 March 2007 15:52, Pawel Jakub Dawidek wrote:
> > > > > What about something like this:
> > > > >
> > > > > #define cv_wait(cv, lock) do {
> > > > > switch (LO_CLASSINDEX((struct lock_object *)(lock))) {
> > > >
> > > > The problem with a cast is you use type checking. Might as well do this:
> > > >
> > > > #define cv_wait(cv, lock) _cv_wait((cv), (struct lock_object *)(lock))
> > >
> > > This will skip type checking and my version only cast to provide type
> > > checking, so when you pass some random variable it will give you an
> > > error.
> >
> > Not really, you may pass some garbage and the LO_CLASSINDEX turns out to be a
> > mutex. :) You only get a runtime error, not a compile-time one.
> > Type-checking by the compiler is nice because you get compile-time errors.
>
> I'll get compile-time error, because cv_wait_mtx() takes
> 'struct condvar *' and 'struct mtx *' as arguments. So even if some
> garbage returns 1, which turns out to be a mutex, call to cv_wait_mtx()
> will generate compile-time error.
However, it has another kind of problem we were trying to avoid: the
first member of the lock you pass should be the struct lock_object. We
should not deal on the ordering of members for locks.
> But it seems the solution may not be that good if it is not very obvious
> on a first look. If typeof() thing works, its fine by me, just give me
> condvar(9) that works with sx(9) locks:)
I think problems with typeof() are 2:
1) It requires a serie of if/else if before to call the cv_wait()
(increase of kernel .text, small slowness, etc.)
2) It is GCC dependant (but we have other of it inside the kernel
alredy, so this is a minor nit)
Attilio
--
Peace can only be achieved by understanding - A. Einstein
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