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Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lo
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lock variant |
Date: |
Wed, 11 Sep 2019 12:56:55 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 |
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
>> 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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- [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 <=
- 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, 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