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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