[jira] [Created] (UIMA-4857) UIMA-AS: Fix NullPointerException

["Jerry Cwiklik (JIRA)" <de...@uima.apache.org>]

Jerry Cwiklik created UIMA-4857:
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             Summary: UIMA-AS: Fix NullPointerException
                 Key: UIMA-4857
                 URL: https://issues.apache.org/jira/browse/UIMA-4857
             Project: UIMA
          Issue Type: Bug
          Components: Async Scaleout
            Reporter: Jerry Cwiklik
            Assignee: Jerry Cwiklik
             Fix For: 2.8.1AS


Fix NPE in the UIMA-AS service caused by a race condition when the service (remote multiplier) sends child CASes to a client. 

For each child it receives, the client sends a message to the service to free the CAS. Upon receipt of the message the service removes CAS from its cache.

The race condition is as follows:
1) Service in Thread 1 sends child CAS to client and the OS suspends the thread.
2) Client immediately sends request to free CAS to the service
3) Service in Thread 2 receives request to free CAS and deletes it from its cache.
4) Service in Thread 1 looks up the CAS in its cache and gets NULL (since the CAS was deleted in 3) above.

So the problem is that right after sending a child CAS to a client, the service tries to access cache entry for this CAS to change the state of the cache entry.

Move the cache look up and state change *before* the send. 




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