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Date: Mon, 12 Mar 2007 21:42:05 +0100
From: Pawel Jakub Dawidek <pjd@FreeBSD.org>
To: John Baldwin <jhb@freebsd.org>
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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
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On Mon, Mar 12, 2007 at 04:18:40PM -0400, John Baldwin wrote:
> 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:
> > > > > >=20
> > > > > > #define cv_wait(cv, lock) do {
> > > > > > switch (LO_CLASSINDEX((struct lock_object *)(lock))) {
> > > > >=20
> > > > > The problem with a cast is you use type checking. Might as well =
do=20
> this:
> > > > >=20
> > > > > #define cv_wait(cv, lock) _cv_wait((cv), (struct lock_object *)(l=
ock))
> > > >=20
> > > > This will skip type checking and my version only cast to provide ty=
pe
> > > > checking, so when you pass some random variable it will give you an
> > > > error.
> > >=20
> > > Not really, you may pass some garbage and the LO_CLASSINDEX turns out=
to=20
> be a=20
> > > mutex. :) You only get a runtime error, not a compile-time one. =20
> > > Type-checking by the compiler is nice because you get compile-time er=
rors.
> >=20
> > 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.
>=20
> Err, no, actually, yours will always give compile errors actually. Keep =
in=20
> mind that LO_CLASSINDEX() is a run-time check. This:
>=20
> #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)
>=20
> Will try to pass 'lock' to three different functions, at least 2 of which=
will=20
> trigger compile errors. :) The kernel won't choose which one to run unti=
l=20
> runtime though. The key is that I want a compile error, not a panic(). :)
Ah, you are right.
--=20
Pawel Jakub Dawidek http://www.wheel.pl
pjd@FreeBSD.org http://www.FreeBSD.org
FreeBSD committer Am I Evil? Yes, I Am!
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