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 >> 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
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