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From Marshall Schor <...@schor.com>
Subject Re: [jira] [Commented] (UIMA-5763) UIMA: need a way to lock a CAS to prevent user from releasing it prematurely
Date Thu, 19 Apr 2018 17:14:31 GMT
I guess these should be posted as Jira comments,  I'll copy the one below, there


On 4/19/2018 1:10 PM, Marshall Schor wrote:
> This all started when a user didn't realize, when using the uima-as
> send-and-receive APIs, that they could not "release" the cas until that
> operation asynchronously completed.
> The original goal was to throw an exception when users accidentally did this. 
> This goal was somewhat expanded when it was realized that any update by "users"
> could conflict with the uima-as asynchronous update that would happen when the
> "receive" part of the asynchronous send=and-receive happened.
> So, the imagined impl is: uima-as sets the no-access mode bit, in it's ansynch.
> send-and-receive, and then when it receives the reply, it updates the cas and
> resets the bit.
> There would need to be perhaps a 2 bit indicator: the prohibit-access bit
> (set/not set), and another bit (privileged), where the setting of 'privileged'
> would be an "internal" API in UIMA, and uima-as would set this when it needed to
> update. 
> This two bit approach avoids a race condition which could occur otherwise.
> I just kind of made up this approach, right now; better ones welcome :-)
> -Marshall
> On 4/18/2018 3:05 PM, Richard Eckart de Castilho (JIRA) wrote:
>>     [ https://issues.apache.org/jira/browse/UIMA-5763?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16443046#comment-16443046
>> Richard Eckart de Castilho commented on UIMA-5763:
>> --------------------------------------------------
>> How would it update the CAS if access is prohibited? 
>> So is it a write(access)-only-by-one-single-thread mode then? I.e. a mode where the
CAS is exclusively owned by a specific thread?
>>> UIMA: need a way to lock a CAS to prevent user from releasing it prematurely
>>> ----------------------------------------------------------------------------
>>>                 Key: UIMA-5763
>>>                 URL: https://issues.apache.org/jira/browse/UIMA-5763
>>>             Project: UIMA
>>>          Issue Type: New Feature
>>>          Components: UIMA
>>>            Reporter: Jerry Cwiklik
>>>            Assignee: Marshall Schor
>>>            Priority: Major
>>>             Fix For: 3.0.1SDK, 2.10.3SDK
>>> UIMA-AS client supports an async style of sending CASes for processing to a remote
service. When using sendCAS( CAS aCas), the code serializes CAS and dispatches it to the remote
but keeps the CAS in a cache. When a reply comes, the cached CAS is used to deserialize a
response. The contract is that the user code should not call CAS.release(). When a reply finally
comes, the CAS is handed over to an application callback and upon return from the callback,
the UIMA-AS releases the CAS. 
>>> Problem: there is nothing to prevent user code to violate the contract. If CAS.release()
is called while UIMA-AS client awaits reply (or during reply deserialization), bad things
happen. In a specific use case, a NPE was thrown during deserialization and debugging was
quite painful.
>>> Proposed solution: to protect integrity of a CAS need a way to lock/unlock it.
Such facility can be added to CASImpl class. When a user code tries to call release()  when
a CAS is locked,  the code should throw an exception (IllegalStateException or similar). 
>>> WDYT?
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