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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 Tue, 03 Jul 2018 21:34:00 GMT

    [ https://issues.apache.org/jira/browse/UIMA-5763?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16531957#comment-16531957

Marshall Schor commented on UIMA-5763:

There are 2 topics in this comment chain:  a "no_access" and "read-only".  The original
impetus was to prevent accidental "releasing" of CASes in uima-as context while the cas was
sent to a remote service. 

The various expansions and augmentations in the comment chain, if implemented, probably slightly
slow down normal CAS operations. 
 * I wonder if it's worth checking on every FS creation or feature update, whether or not
a global (to the CAS) read-only flag is set.  
 * I wonder if it's worth checking on every index or feature access, whether or not a no-access
flag is set.

Doing the original request (preventing a user from accidentally releasing a CAS) is a very
low frequency operation, so no performance impact would be expected.

For the next release, I'll make a new Jira, which will cover a minimal implementation of the
original intent (preventing accidental releasing of CASes), and leave this Jira open, in case
we figure out a good approach on going forward with read-only / no-access that won't impact

> 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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