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

[Pawel Jakub Dawidek]

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:
> > > > > > 
> > > > > > #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(). :)

Ah, you are right.

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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