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From Isuru Haththotuwa <isu...@apache.org>
Subject Re: [Discuss] Hierarchical Locking for Topology
Date Mon, 13 Oct 2014 12:20:54 GMT
Another improvement that we can do is to introduce the same hierarchical
locking to the Topology structure maintained in the Cloud Controller. Its
actually the CC who will be updating the local Topology and sending the
relevant events. In that case, if we have have only one write lock for the
whole Topology in the CC's TopologyBuilder, it will still be a bottleneck.
WDYT?

On Thu, Oct 9, 2014 at 3:36 PM, Isuru Haththotuwa <isuruh@apache.org> wrote:

> Hi,
>
>
> Since the Topology is updated from the messaging component only, I removed
> the methods to access the write locks to an internal class. Those methods
> will not be exposed to outside by the messaging component. Now, the
> following methods to obtain read-only locks are exposed from
> TopologyManager:
>
>     // Topology level read locks
>
>     /**
>      * Acquires read lock for the Complete Topology
>      */
> *    public static void acquireReadLock() ;*
>
>     /**
>      * Releases read lock for the Complete Topology
>      */
> *    public static void releaseReadLock();*
>
>     // Application and Service read locks
>
>     /**
>      * Acquires read lock for the all Applications
>      */
> *    public static void acquireReadLockForApplications() ;*
>
>     /**
>      * Releases read lock for the all Applications
>      */
> *    public static void releaseReadLockForApplications();*
>     /**
>      * Acquires read lock for the all Services
>      */
> *    public static void acquireReadLockForServices();*
>
>     /**
>      * Releases read lock for the all Services
>      */
> *    public static void releaseReadLockForServices() ;*
>
>     /**
>      * Acquires read lock for a Service
>      *
>      * @param serviceName service name to acquire read lock
>      */
> *    public static void acquireReadLockForService (String serviceName) ;*
>
>     /**
>      * Releases read lock for a Service
>      *
>      * @param serviceName service name to release read lock
>      */
> *    public static void releaseReadLockForService (String serviceName) ;*
>
>     /**
>      * Acquires read lock for a Cluster. This will acquire the read lock
> in the following order
>      *      1. for the Service
>      *      2. for the Cluster
>      *
>      * @param serviceName service name to acquire read lock
>      * @param clusterId cluster id to acquire read lock
>      */
> *    public static void acquireReadLockForCluster (String serviceName,
> String clusterId);*
>
>     /**
>      * Releases read lock for a Cluster. This will release the read lock
> in the following order
>      *      1. for the Cluster
>      *      2. for the Service
>      *
>      * @param serviceName service name to release read lock
>      * @param clusterId cluster id to release read lock
>      */
> *    public static void releaseReadLockForCluster (String serviceName,
> String clusterId);*
>
>     /**
>      * Acquires read lock for the Application
>      *
>      * @param appId Application id
>      */
> *    public static void acquireReadLockForApplication (String appId) ;*
>
>     /**
>      * Releases read lock for the Application
>      *
>      * @param appId Application id
>      */
> *    public static void releaseReadLockForApplication (String appId);*
>
>
>
>
>
> On Mon, Oct 6, 2014 at 2:51 PM, Imesh Gunaratne <imesh@apache.org> wrote:
>
>> This looks great! As we discussed may be we could provide an interface in
>> the messaging component to acquire and release locks at different sub tree
>> levels. The whole idea is to avoid any possibilities of reading the
>> topology in an inconsistent state.
>>
>> Thanks
>>
>> On Mon, Oct 6, 2014 at 12:37 PM, Isuru Haththotuwa <isuruh@apache.org>
>> wrote:
>>
>>> 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/>*
>>>>
>>>>
>>>>
>>
>>
>> --
>> Imesh Gunaratne
>>
>> Technical Lead, WSO2
>> Committer & PMC Member, Apache Stratos
>>
>> --
>> Thanks and Regards,
>>
>> Isuru H.
>> +94 716 358 048
>>
>> --
>> Thanks and Regards,
>>
>> Isuru H.
>> +94 716 358 048* <http://wso2.com/>*
>>
>>
>> * <http://wso2.com/>*
>>
>>
>>

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