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

[John Baldwin]

On Saturday 10 March 2007 15:52, Pawel Jakub Dawidek wrote:
> On Sat, Mar 10, 2007 at 12:44:26PM +0100, Attilio Rao wrote:
> > 2007/3/9, John Baldwin <jhb at freebsd.org>:
> > >I don't have a date set for removing msleep(), esp. given it's wide use.
> > >I would like to remove it and all the spl*() functions in 8.0 if we can
> > >swing it.
> > >
> > >I also have patches to let condition variables work with rwlocks and sx
> > >locks, but the current implementation results in an API "explosion"
> > >since each of the cv_*wait*() functions grows a cv_*wait*_rw() version 
for
> > >rwlocks and a cv_*waut*_sx() version for use with sx locks.  One 
possibility
> > >would be to just cast the lock argument to (struct lock_object *) since 
all
> > >of our locks have a lock_object as the first member, but then you use 
having
> > >the compiler do type checking, and I'm really not willing to give up on
> > >that.  Too easy to have evil bugs that way.  I suppose we could use some
> > >evil macro that used typeof() but that would be very gcc specific?
> > >
> > >I guess one other possibility is to standardize on the field name for
> > >the lock_object, calling it lo_object instead of mtx_object, rw_object,
> > >sx_object, etc.  Anyone else have any ideas?
> > 
> > What about adding a new function like:
> > 
> > static __inline struct lock_object *
> > mtx_export_lc(struct mtx *m)
> > {
> > 
> >        return (&m->mtx_object);
> > }
> > 
> > to be per-interface (so having sx_export_lc() and rw_export_lc() too)
> > and than using in this way:
> > 
> > static struct mtx foo_lock;
> > static struct cv foo_cv;
> > ...
> > 
> > mtx_lock(&foo_lock);
> > ...
> > cv_wait(&foo_cv, mtx_export_lc(&foo_lock));
> > 
> > (obviously using new struct lock_object methods you added for 
locking/unlocking)
> > 
> > It sounds reasonable to you?
> 
> This is ugly. If we really need to provide information about which type
> of lock we are using, I'd probably prefer cv_wait_<locktype>().
> 
> 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))

> PS. I'd really like to be able to use condvar(9) with sx(9) locks,
> because currently I've to manage mu own condvar(9) version for ZFS
> that does exactly this.

The patch is already done in //depot/jhb/lock/..., just need to settle on the 
API.

-- 
John Baldwin