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From Peter Monks <pmo...@alfresco.com>
Subject Re: OpenCMIS: should Session extend Serializable?
Date Wed, 08 Jun 2011 15:42:05 GMT
Thanks for the clarification Florent.

Question for you - if Session was Serializable, couldn't org.nuxeo.ecm.core.opencmis.impl.client.NuxeoSession
hold a transient reference to the non-serializable objects, with the "connection" re-estalished
automatically post-deserialization?  Presumably this would require some serialization of the
session parameters, but generally speaking those are fairly small / lightweight.

Cheers,
Peter



On Jun 8, 2011, at 8:11 am, Florent Guillaume wrote:

> Hi Peter,
> 
> FYI, here's an example of non-Serializable Session implementation:
> Nuxeo plugins can use OpenCMIS APIs directly in same-JVM mode (without
> a networking layer being invoked), using
> org.nuxeo.ecm.core.opencmis.impl.client.NuxeoSession. This
> implementation of Session holds (indirectly) a reference to a
> non-Serializable low-level connection-like object (think
> java.sql.Connection), that by definition is not Serializable.
> 
> Florent
> 
> 
> On Thu, Jun 2, 2011 at 9:21 PM, Peter Monks <pmonks@alfresco.com> wrote:
>> Thanks Florian.  I'm still a little confused though - if Session is not Serializable,
how can I rely on an arbitrary Session implementation class being Serializable?  What if someone
configures my client to use one of these non-Chemistry Session implementations?
>> 
>> Possible workarounds include:
>> Checking whether the implementation class is an instanceof Serializable, and not
caching it if it isn't (which implies poor performance for Session implementations that aren't
serializable)
>> Wrapping Session in a Serializable wrapper that has a transient reference to the
Session (Session will be cached as long as it's kept in memory by the JVM - as soon as the
cache serializes a Session for whatever reason, that Session will effectively become decached
and incur the creation cost next time that user does something that requires CMIS)
>> 
>> In the specific client I'm working on right now I can live with either workaround,
but in general (and imho) they are both quite undesirable given that this is likely to be
a common use case.  I notice for example that the Liferay guys identified a need for Session
caching in their "CMIS Document Library" implementation (see [1], in particular the comments).
 We can probably assume that either the Liferay cache doesn't require items to be Serializable,
or they worked around it in something like one of the two ways described above.
>> 
>> Thinking along different lines for a moment - why does creating a Session have to
hit the CMIS server at all - is it to validate the username and password?  If so, is it worth
delaying that check until the first "real" CMIS call, thereby significantly reducing the cost
of establishing a Session (i.e. by eliminating any RPCs to the CMIS server at Session creation
time)?  This could even be configured via a flag to the SessionFactory to preserve backwards
compatibility.
>> 
>> Cheers,
>> Peter
>> 
>> [1] http://www.liferay.com/web/alexander.chow/blog/-/blogs/7670631
>> 
>> 
>> 
>> 
>> On Jun 2, 2011, at 2:26 am, Florian Müller wrote:
>> 
>>> Hi Peter,
>>> 
>>> We had some discussions about that in the past. There are actually other implementations
of the OpenCMIS interfaces (not part of Apache Chemistry) that can not and need not be serializable.
We don't want to force them to do something crazy just to implement the OpenCMIS interfaces.
>>> 
>>> The OpenCMIS classes have been designed to be serializable from the start to
support HTTP sessions. Casting to Serializable is safe now and will be safe in the future
-- even though it might feel weird.
>>> 
>>> What surprises me is that creating a session takes several seconds. Connecting
to a Alfresco server on a local network takes about 100ms. If it takes significantly longer
then there is something wrong...
>>> 
>>> 
>>> Florian
>>> 
>>> 
>>> On 01/06/2011 23:35, Peter Monks wrote:
>>>> G'day everyone,
>>>> 
>>>> Creating an org.apache.chemistry.opencmis.client.api.Session is quite an
expensive operation (it typically takes several seconds), so I'm looking to cache Session
objects in a per-user cache in my client app so that I don't have to recreate Sessions for
every single interaction with the CMIS server.
>>>> 
>>>> Unfortunately the cache library I'm using requires that cached objects implement
java.io.Serializable, which Session does not.  However the default implementation class (org.apache.chemistry.opencmis.client.runtime.SessionImpl)
does in fact implement Serializable, allowing me the workaround of casting the Session object
to Serializable prior to adding to the cache.  I'm not particularly comfortable with this
approach however, given that this seems to be an implementation detail and not officially
part of the contract for Sessions.
>>>> 
>>>> Is there a compelling reason that Session doesn't implement Serializable?
 Is this something that could be added (noting that this change is backwards compatible)?
>>>> 
>>>> Thanks in advance,
>>>> Peter
>>>> 
>>>> 
>>> 
>> 
>> 
> 
> 
> 
> -- 
> Florent Guillaume, Director of R&D, Nuxeo
> Open Source, Java EE based, Enterprise Content Management (ECM)
> http://www.nuxeo.com   http://www.nuxeo.org   +33 1 40 33 79 87


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