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From Jozef Vilcek <jozo.vil...@gmail.com>
Subject Re: Persistent locks
Date Fri, 17 Jan 2014 07:20:58 GMT
Jordan,

so, do you think it is feasible to do such changes into Curator locks? Via
changes into LockInternalsDriver? If yes, should I go ahead and create a
JIRA and draft a patch?

Best,
Jozef


On Wed, Jan 15, 2014 at 12:06 PM, Jozef Vilcek <jozo.vilcek@gmail.com>wrote:

> Yes. I was digging a bit in curator code and thinking about how can I
> implement this. If I would be able to somehow intercept creation of lock
> nodes, I could build GC/heartbeat logic around the lock by "installing"
> appropriate hooks.
>
> One idea is that lock would accept a kind of LockNodeFactory, which would
> be responsible for creating actual zookeeper nodes.
> LockInternals.attemptLock() would delegate construction to the factory.
> There, in my own factory, I could add posibility to listen to created lock
> nodes and apply GC/heartbeat logic.
>
> As you suggested, same could be done if node creation would be moved to
> the LockInternalsDriver and made public/reusable. I like this even better.
> It could be tricky how to reuse e.g. read-write lock, but it would not be
> so painful to "re-implement" only that part of curator code on my end.
>
>
> Jozo
>
>
> On Tue, Jan 14, 2014 at 6:51 PM, Jordan Zimmerman <
> jordan@jordanzimmerman.com> wrote:
>
>> You might be able to re-use the code in the LockInternals class. It could
>> easily be modified to do what you want via the LockInternalsDriver. Of
>> course it would need to be made public. The gc/heartbeat stuff would have
>> to be coded fresh, though.
>>
>> -Jordan
>>
>> ------------------------------
>> From: Jozef Vilcek Jozef Vilcek <jozo.vilcek@gmail.com>
>> Reply: Jozef Vilcek jozo.vilcek@gmail.com
>> Date: January 14, 2014 at 12:18:15 AM
>> To: Jordan Zimmerman jordan@jordanzimmerman.com
>> Subject:  Re: Persistent locks
>>
>> Yes, you are correct. I tried to sketch this in my post. There will be
>> possibility to create persistent lock, which will cause deadlock if holder
>> crashes and one with possibility to to be gc collected after some time if
>> holder crashes. The mechanism for this has to be implemented.
>>
>> Off course that I use "classical" ephemeral locks where possible. But I
>> have few cases where it is not feasible.
>>
>>
>> On Tue, Jan 14, 2014 at 2:42 AM, Jordan Zimmerman <
>> jordan@jordanzimmerman.com> wrote:
>>
>>>  How will you avoid dead locks? You’ll need to write some kind of
>>> heartbeat/gc mechanism to the lock. Otherwise I don’t see how it works if
>>> the lock holder crashes.
>>>
>>>  -JZ
>>>
>>>  ------------------------------
>>> From: Jozef Vilcek Jozef Vilcek <jozo.vilcek@gmail.com>
>>> Reply: user@curator.apache.org user@curator.apache.org
>>> Date: January 13, 2014 at 7:24:06 AM
>>> To: user@curator.apache.org user@curator.apache.org
>>> Subject:  Persistent locks
>>>
>>>   Hi
>>>
>>> I have a question about curator locks. I see that locks are implemented
>>> via znode type EPHEMERAL_SEQUENTIAL. I am thinking about having an
>>> implementation via PERSISTENT_SEQUENTIAL.
>>>
>>> Main reason for this are processes with critical sections, where we can
>>> not afford to loose a lock due to session expiration. In such case, others
>>> might acquire a lock and kick in while the previous process is still
>>> running but e.g. experiencing connection issues. To kill this temporally
>>> detached process in favor of others would be too costly.
>>>
>>> My thoughts are to have:
>>>
>>> * Persistent lock - if something go south and client code does not
>>> release lock, it will stay there until removed by manual or some other
>>> intervention
>>>
>>> * Persistent ephemeral lock - this would be ephemeral implemented by
>>> persistent lock. For not so much critical stuff but e.g. for unstable
>>> environments. This would install kind of refresh hook on a created lock
>>> node. Other clients waiting to acquire lock could garbage collect locks
>>> which does not received refresh for reasonable long time (scaling beyond
>>> session timeouts).
>>>
>>> What I would like to know:
>>>
>>> * any wisdom, if this does make sense or if there is a better way out
>>> there
>>> * support from curator ... There is a lot of good code in curator I
>>> would have to copy to make this work. I want to avoid this. Would it be
>>> possible of provide either path for making locks core extensible/reusable
>>> (or to contribute implementation of locks if considered worth for
>>> framework) ?
>>>
>>>
>>> Best,
>>> Jozo
>>>
>>>
>>
>

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