Re: [jgroups-users] questions about CENTRAL_LOCK locking service under 3.6.11

On 12/10/17 4:12 PM, Questions/problems related to using JGroups wrote:
>> If you look at the coordinator, does it list all locks?
> The coordinator (i-06b66037ffd44d0fb) has the lock in the server and my sections (via printLocks).
>
> 	server locks: engradeSynchronizationTask: i-06b66037ffd44d0fb::107
> 	my locks: engradeSynchronizationTask (i-06b66037ffd44d0fb::107)
>
> 1st backup (i-040062a23b224bb64) and 2nd backup (i-0d42875495a3cb64f) has no my locks.
>
> 	server locks: engradeSynchronizationTask: i-06b66037ffd44d0fb::107
> 	my locks:
>
> Is the my-lock asymmetry expected?  Does it imply that the server is holding the lock or just that it is managing it?

Yes, this means the coordinator and backup have the server lock, but the 
coord itself actually _holds_ the lock. This is perfectly fine.

>
>> Note that the lock service in JGroups _can_ lead to multiple owners holding the same lock at the same time in case of a split brain. You'd have to resort to jgroups-raft to enforce at-most-once semantics.
> It looks like the cluster members have a consistent view so I think I don't have split brain.
>
>> Take a look at [1] and go from 3.6.12 to 3.6.14
> I've gone to 3.6.14 and I believe I'm seeing the same issues.
> gray
>
>
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-- 
Bela Ban, JGroups lead (http://www.jgroups.org)


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