Re: [Qemu-block] [Qemu-devel] [PATCH 02/10] qemu-thread: introduce QemuLockCnt

[Eric Blake]

On 11/29/2016 05:46 AM, Paolo Bonzini wrote:
> A QemuLockCnt comprises a counter and a mutex, with primitives
> to increment and decrement the counter, and to take and release the
> mutex.  It can be used to do lock-free visits to a data structure
> whenever mutexes would be too heavy-weight and the critical section
> is too long for RCU.
> 
> This could be implemented simply by protecting the counter with the
> mutex, but QemuLockCnt is harder to misuse and more efficient.
> 
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---


> +    int qemu_lockcnt_count(QemuLockCnt *lockcnt);
> +
> +        Return the lockcnt's count.  The count can change at any time
> +        any time; still, while the lockcnt is locked, one can usefully

duplicate 'any time'


> +++ b/util/lockcnt.c
> @@ -0,0 +1,113 @@
> +/*
> + * QemuLockCnt implementation
> + *
> + * Copyright Red Hat, Inc. 2015

You've been sitting on this a while :)  Want to add 2016?

The documentation is a huge help to understanding the code; overall it
looks pretty clean.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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