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From Isuru Haththotuwa <isu...@apache.org>
Subject Re: [Discuss] Hierarchical Locking for Topology
Date Mon, 06 Oct 2014 07:07:29 GMT
Thanks Imesh.

I have shown some examples for the new hierarchical locking approach.
Please do let me know your feedback on this.

   Acquire a write lock:

   From root level, acquire read lock, and acquire a write lock only for the
   relevant sub tree.

   Acquire a read lock:

   From root level, acquire read locks till the relevant sub tree

   Examples -

   Example 1: Acquiring write lock for a Cluster to modify the Cluster
object -
            acquiring:
            1. acquire read lock for all Services
            2. acquire read lock for the particular Service, to which the
cluster belongs to
            3. acquire write lock for the Cluster

            releasing:
            1. release write lock for the Cluster
            2. release read lock for the particular Service
            3. release read lock for all Services

   Example 2: Acquiring write lock to add a new Cluster object -
            acquiring:
            1. acquire read lock for all Services
            2. acquire write lock for the particular Service, to which the
cluster belongs to

            releasing:
            1. release write lock for the particular Service
            2. release read lock for all Services

   Example 3: Acquiring read lock to read Cluster information
            acquiring:
            1. acquire read lock for all Services
            2. acquire read lock for the particular Service, to which the
cluster belongs to
            3. acquire read lock for the relevant Cluster

            releasing:
            1. release read lock for the relevant Cluster
            2. release read lock for the particular Service
            3. release read lock for all Services

   Example 4: Acquiring the write lock to add a deploy a Cartridge (add a
new Service)
            acquire:
            1. acquire write lock for all Services

            release:
            1. release write lock for all Services

In all of these examples, the lock acquiring happens from top of the tree
to down. This is to avoid deadlocks.

On Mon, Oct 6, 2014 at 10:50 AM, Imesh Gunaratne <imesh@apache.org> wrote:

> Great! Thanks for the clarification Isuru!
>
> Yes I agree, I think what we can do is, identify the sub trees that will
> not break the consistency of the data structure and manage locks at those
> sub tree level.
>
> Thanks
>
> On Sun, Oct 5, 2014 at 8:07 PM, Isuru Haththotuwa <isuruh@apache.org>
> wrote:
>
>> Hi Lahiru and Imesh,
>>
>> Thanks a lot for the input.
>>
>> What I do here is locking only the relevant sub tree of the complete
>> Topology tree, as locking the whole tree is rather inefficient. For an
>> example, when a MemberActivated event is received, we have the cluster id
>> of the cluster that particular member belongs to. IMHO, we only need to
>> acquire the write lock for that cluster , and do not need the lock for
>> complete Topology tree. Therefore, any other thread which needs to do
>> another operation on a separate sub tree (for an example, deploy a new
>> service, etc.) can do that concurrently.
>>
>> On Sun, Oct 5, 2014 at 12:20 AM, Lahiru Sandaruwan <lahirus@wso2.com>
>> wrote:
>>
>>> Hi Isuru,
>>>
>>> Looks like a good move to improve the efficiency,
>>>
>>> On Fri, Oct 3, 2014 at 3:05 PM, Isuru Haththotuwa <isuruh@apache.org>
>>> wrote:
>>>
>>>> I did the initial changes, at the testing phase now. For an example, if
>>>> we need to add a new Service, we do not need to lock everything now. We an
>>>> only acquire the write lock on Services, and add the Service.
>>>>
>>>
>>> Service can be an element of a group or an app. So shouldn't we lock
>>> complete application if we add/modify a service? Otherwise a different
>>> thread might change parents/relationships otherwise.
>>>
>> AFAIK a Service gets created when we deploy a cartridge. An
>> application/Group can refer a service. In the case of modifying an
>> Application, we do need to lock the relevant clusters that belong to that
>> Application. I implemented that.
>>
>>>
>>> So generally i think we can bring down the locking level to Application,
>>> but not the services. Also if we need to read any part, we have to get the
>>> read lock for the whole topology, such that the receiver get a particular
>>> snapshot of the topology as Imesh also mentioned.
>>>
>> If we need to lock the complete Topology, we can still do that, such as
>> in a Complete Topology event. But IMHO, if we know the exact part (a
>> particular Cluster, etc.) that we need to read/write, we do not need to
>> lock the whole Topology.
>>
>>>
>>> Thanks.
>>>
>>> If we need to modify a particular Service, can read lock the Services
>>>> and acquire the write lock on the relevant Service and do the modification.
>>>>
>>> This support is there for Services, Cluster and Applications.
>>>>
>>>
>>>> On Wed, Oct 1, 2014 at 9:27 PM, Manula Chathurika Thantriwatte <
>>>> manulac@wso2.com> wrote:
>>>>
>>>>> Hi Isuru,
>>>>>
>>>>> +1 for the hierarchical locking approach. Using hierarchical locking
>>>>> we can have more benefits [1].
>>>>>
>>>>> [1]
>>>>> http://synapticnulship.com/blog/2013/03/08/comparison-chainlocker-vs-heirarchical-mutexes/
>>>>>
>>>>>
>>>>> On Wed, Oct 1, 2014 at 7:46 PM, Isuru Haththotuwa <isuruh@apache.org>
>>>>> wrote:
>>>>>
>>>>>> Hi Devs,
>>>>>>
>>>>>> In the current Topology implementation, we acquire read/write locks
>>>>>> on Topology from the root level itself. For an example, if we need
to
>>>>>> modify a single Cluster object, we still need to acquire a write
lock from
>>>>>> the Topology root level. But, this is a costly operation. Specially,
with
>>>>>> Service Grouping changes, we would need to traverse through an Application.
>>>>>> Since an Application can be a recursive structure, it can be a time
>>>>>> consuming operation. in such a scenario, if we are to lock the whole
>>>>>> Topology, there will be many threads waiting on that lock.
>>>>>>
>>>>>> As a solution, I think we can use hierarchical locking [1]. For an
>>>>>> example, when you need to obtain the write lock for a particular
>>>>>> Application, you do not need to lock the whole tree, but can lock
only that
>>>>>> Application itself. However, still we need to get the read locks
for the
>>>>>> parents.
>>>>>>
>>>>>> A separate Lock tree will be maintained for the Topology.
>>>>>>
>>>>>> Please share your feedback.
>>>>>>
>>>>>> [1].
>>>>>> http://collaboration.cmc.ec.gc.ca/science/rpn/biblio/ddj/Website/articles/DDJ/2008/0801/071201hs01/071201hs01.html
>>>>>>
>>>>>> --
>>>>>> Thanks and Regards,
>>>>>>
>>>>>> Isuru H.
>>>>>> +94 716 358 048* <http://wso2.com/>*
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Regards,
>>>>> Manula Chathurika Thantriwatte
>>>>> Software Engineer
>>>>> WSO2 Inc. : http://wso2.com
>>>>> lean . enterprise . middleware
>>>>>
>>>>> email : manulac@wso2.com / manula@apache.org
>>>>> phone : +94 772492511
>>>>> blog : http://manulachathurika.blogspot.com/
>>>>>
>>>>> --
>>>>> <http://manulachathurika.blogspot.com/>
>>>>> Thanks and Regards,
>>>>>
>>>>> Isuru H.
>>>>> <http://manulachathurika.blogspot.com/>
>>>>> +94 716 358 048 <http://manulachathurika.blogspot.com/>*
>>>>> <http://wso2.com/>*
>>>>>
>>>>>
>>>>> * <http://wso2.com/>*
>>>>>
>>>>>
>>>>>
>>>
>>>
>>> --
>>> --
>>> Lahiru Sandaruwan
>>> Committer and PMC member, Apache Stratos,
>>> Senior Software Engineer,
>>> WSO2 Inc., http://wso2.com
>>> lean.enterprise.middleware
>>>
>>> email: lahirus@wso2.com cell: (+94) 773 325 954
>>> blog: http://lahiruwrites.blogspot.com/
>>> twitter: http://twitter.com/lahirus
>>> linked-in: http://lk.linkedin.com/pub/lahiru-sandaruwan/16/153/146
>>>
>>> --
>>> <http://lk.linkedin.com/pub/lahiru-sandaruwan/16/153/146>
>>> Thanks and Regards,
>>>
>>> Isuru H.
>>> <http://lk.linkedin.com/pub/lahiru-sandaruwan/16/153/146>
>>> +94 716 358 048
>>> <http://lk.linkedin.com/pub/lahiru-sandaruwan/16/153/146>*
>>> <http://wso2.com/>*
>>>
>>>
>>> * <http://wso2.com/>*
>>>
>>>
>>>
>
>
> --
> Imesh Gunaratne
>
> Technical Lead, WSO2
> Committer & PMC Member, Apache Stratos
>
> --
> Thanks and Regards,
>
> Isuru H.
> +94 716 358 048* <http://wso2.com/>*
>
>
> * <http://wso2.com/>*
>
>
>

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