On Monday 12 March 2007 16:17, Attilio Rao wrote:
> 2007/3/12, Pawel Jakub Dawidek <[EMAIL PROTECTED]>:
> > 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.)
The compiler should optimize those out actually to a single call to
_cv_wait(), just as it does with PCPU_*().
> 2) It is GCC dependant (but we have other of it inside the kernel
> alredy, so this is a minor nit)
That is the only really big nit.
--
John Baldwin
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