* Eric Blake (ebl...@redhat.com) wrote: > On 9/11/19 11:56 AM, Daniel P. Berrangé 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 > > spurious double space > > >> g_auto infrastrcture (and thus whatever the compilers hooks are) to > > infrastructure > compiler's
Thanks. Dave > >> release it on all exits of the block. > >> > >> Note this macro has a variable declaration in, and hence is not in > >> a while loop. > >> > > >> +#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(); > > Another pattern to consider: nbdkit uses: > > #define ACQUIRE_LOCK_FOR_CURRENT_SCOPE(mutex) \ > CLEANUP_UNLOCK pthread_mutex_t *_lock = mutex; \ > do { \ > int _r = pthread_mutex_lock (_lock); \ > assert (!_r); \ > } while (0) > > with later code calling: > > ACQUIRE_LOCK_FOR_CURRENT_SCOPE (&lock); > > > > > 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) > > Yes, this aspect of glib is nicer than the corresponding nbdkit usage > pattern. > > -- > Eric Blake, Principal Software Engineer > Red Hat, Inc. +1-919-301-3226 > Virtualization: qemu.org | libvirt.org > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
