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Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lo
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lock variant |
Date: |
Wed, 11 Sep 2019 19:49:50 +0100 |
User-agent: |
Mutt/1.12.1 (2019-06-15) |
* Eric Blake (address@hidden) 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" <address@hidden>
> >>
> >> 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 / address@hidden / Manchester, UK
- [Qemu-devel] [PATCH 0/3] Automatic RCU read unlock, Dr. David Alan Gilbert (git), 2019/09/11
- [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lock variant, Dr. David Alan Gilbert (git), 2019/09/11
- Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lock variant, Daniel P . Berrangé, 2019/09/11
- Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lock variant, Dr. David Alan Gilbert, 2019/09/11
- Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lock variant, Daniel P . Berrangé, 2019/09/11
- Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lock variant, Dr. David Alan Gilbert, 2019/09/11
- Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lock variant, Daniel P . Berrangé, 2019/09/11
- Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lock variant, Dr. David Alan Gilbert, 2019/09/11
- Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lock variant, Eric Blake, 2019/09/11
- Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lock variant,
Dr. David Alan Gilbert <=
Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lock variant, Eric Blake, 2019/09/11
Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lock variant, Dr. David Alan Gilbert, 2019/09/11
[Qemu-devel] [PATCH 2/3] migration: Use automatic rcu_read unlock in ram.c, Dr. David Alan Gilbert (git), 2019/09/11
[Qemu-devel] [PATCH 3/3] migration: Use automatic rcu_read unlock in rdma.c, Dr. David Alan Gilbert (git), 2019/09/11
Re: [Qemu-devel] [PATCH 0/3] Automatic RCU read unlock, Daniel P . Berrangé, 2019/09/11