Date: Mon, 12 Mar 2007 16:18:40 -0400 From: John Baldwin <jhb@freebsd.org> To: Pawel Jakub Dawidek <pjd@freebsd.org> Cc: Attilio Rao <attilio@freebsd.org>, cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@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: <200703121618.41084.jhb@freebsd.org> In-Reply-To: <20070312200345.GB5688@garage.freebsd.pl> References: <200703092241.l29Mf2Ds062856@repoman.freebsd.org> <200703121535.22140.jhb@freebsd.org> <20070312200345.GB5688@garage.freebsd.pl>
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On Monday 12 March 2007 16:03, Pawel Jakub Dawidek wrote:
> 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.
Err, no, actually, yours will always give compile errors actually. Keep in
mind that LO_CLASSINDEX() is a run-time check. This:
#define cv_wait(cv, lock) do {
switch (LO_CLASSINDEX((struct lock_object *)(lock))) {
case 1:
cv_wait_mtx(cv, lock);
break;
case 2:
cv_wait_sx(cv, lock);
break;
case 3:
cv_wait_rw(cv, lock);
break;
default:
panic("Invalid lock.");
}
} while (0)
Will try to pass 'lock' to three different functions, at least 2 of which will
trigger compile errors. :) The kernel won't choose which one to run until
runtime though. The key is that I want a compile error, not a panic(). :)
--
John Baldwin
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