Andrew Dinn commented on JBTM-599:
I looked further into this and managed to isolate the problem. Each of the test threads
does an add then a delete of an object store record. I used a byteman script to allow 50
threads to proceed and then stall the next 50 threads for a few seconds at the call to
add.Work This caused the stall to happen every time I ran the test.
The remove operations alter the wait condition state because they increase the number of
pending remove operations. This can cause the condition test made in addWork to see the
cache as full. However, the removing threads do not test the condition and notify the
AsyncCache thread when the state changes to full.
So, the AsyncStore thread can deplete the queue of all pendiing adds and removes and then
go into a wait. If this is followed by enough removes with no adds then the cache fills
and further adds are stalled. This leaves them stalled until the AsyncStore thread wakes
The fix is to test the wait condition during remove and, if the cache is full notify the
Synchronization problem in CacheStore
Project: JBoss Transaction Manager
Issue Type: Bug
Security Level: Public(Everyone can see)
Components: Transaction Core
Affects Versions: 4.7.0
Reporter: Andrew Dinn
This bug manifests occasionally when running the CachedTest. The AsyncStore thread
suspends inside its run method on a (120 sec) timed wait because the cache is not full.
When I managed to catch this case in the debugger I found that there were many writer
threads (~30) suspended inside addWork in an untimed wait on the overflow lock. So, these
writing threads make no progress for 120 seconds. The AsyncStore thread does notify the
object on which the writers are waiting but there is clearly a window where the writers
can go to sleep while the cache is full and not get notified when the AsyncStore thread
has emptied it.
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