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From "Marshall Schor (JIRA)" <...@uima.apache.org>
Subject [jira] [Commented] (UIMA-5763) UIMA: need a way to lock a CAS to prevent user from releasing it prematurely
Date Thu, 19 Apr 2018 20:22:00 GMT

    [ https://issues.apache.org/jira/browse/UIMA-5763?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16444730#comment-16444730

Marshall Schor commented on UIMA-5763:

So here's the current thought of how this could be implemented.
 # add a mode bit to the CAS, called no_access.  APIs for setting/resetting/reading this
will be "internal use only", so won't normally be used by ordinary users.
 # for operations that modify the CAS, including calling reset, if no_access is set, do a
further check:
 ## An "internal use only" API is provided to specify a "privileged" thread.  If the thread
doing the operation is this one, permit the operation; otherwise, throw an exception.

uima-as picks up and processes the received CAS on an arbitrary thread, but then sets that
into the CAS before deserializing.

> 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). 

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