* Daniel P. Berrangé (berra...@redhat.com) wrote: > On Wed, Sep 11, 2019 at 05:42:00PM +0100, Dr. David Alan Gilbert (git) wrote: > > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com> > > > > RCU_READ_LOCK_AUTO takes the rcu_read_lock and then uses glib's > > g_auto infrastrcture (and thus whatever the compilers hooks are) to > > release it on all exits of the block. > > > > Note this macro has a variable declaration in, and hence is not in > > a while loop. > > > > Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com> > > --- > > include/qemu/rcu.h | 12 ++++++++++++ > > 1 file changed, 12 insertions(+) > > > > diff --git a/include/qemu/rcu.h b/include/qemu/rcu.h > > index 22876d1428..6a25b27d28 100644 > > --- a/include/qemu/rcu.h > > +++ b/include/qemu/rcu.h > > @@ -154,6 +154,18 @@ extern void call_rcu1(struct rcu_head *head, RCUCBFunc > > *func); > > }), \ > > (RCUCBFunc *)g_free); > > > > +typedef char rcu_read_auto_t; > > +static inline void rcu_read_auto_unlock(rcu_read_auto_t *r) > > +{ > > + rcu_read_unlock(); > > +} > > + > > +G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC(rcu_read_auto_t, rcu_read_auto_unlock) > > > > +#define RCU_READ_LOCK_AUTO g_auto(rcu_read_auto_t) \ > > + _rcu_read_auto = 'x'; \ > > + rcu_read_lock(); > > + > > Functionally this works, but my gut feeling would be to follow > the design of GMutexLocker as-is: > > https://developer.gnome.org/glib/stable/glib-Threads.html#g-mutex-locker-new > > so you get a use pattern of > > g_autoptr(rcu_read_locker) locker = rcu_read_locker_new(); > > This makes it explicit that the code is creating a variable here, which > in turns means it is clear to force unlock early with > > g_clear_pointer(&locker, rcu_read_locker_free)
The difference compared to the g-mutex-locker is that I don't have another object to use as my pointer; that uses the address of the GMutex as the dummy pointer value. I did try an experiment with g_autoptr and found that it did need to return a non-NULL value for it to work, which then lead me to think what value to use - while it seems to work if I return (void *)1 it makes me nervous. Dave > > > Regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK