Hi,
I recently discovered what may be responsible for frequent deadlocks of an
application here. In the "jstack -l" output, I see almost all threads waiting
on a single ReentrantLock, and this thread is what holds that lock:
"WorkerThread4" prio=5 tid=103bc9000 nid=0x132caf000 in Object.wait()
[132cae000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <22711d098> (a
com.webobjects.appserver.WOSessionStore$TimeoutEntry)
at java.lang.Object.wait(Object.java:485)
at
com.webobjects.appserver.WOSessionStore.checkOutSessionWithID(WOSessionStore.java:191)
- locked <22711d098> (a
com.webobjects.appserver.WOSessionStore$TimeoutEntry)
at
com.webobjects.appserver.WOApplication.restoreSessionWithID(WOApplication.java:1913)
at
er.extensions.appserver.ERXApplication.restoreSessionWithID(ERXApplication.java:2440)
at
er.extensions.appserver.ERXComponentRequestHandler._dispatchWithPreparedApplication(ERXComponentRequestHandler.java:260)
at
er.extensions.appserver.ERXComponentRequestHandler._handleRequest(ERXComponentRequestHandler.java:302)
at
er.extensions.appserver.ERXComponentRequestHandler.handleRequest(ERXComponentRequestHandler.java:377)
at
com.webobjects.appserver.WOApplication.dispatchRequest(WOApplication.java:1687)
at
er.extensions.appserver.ERXApplication.dispatchRequestImmediately(ERXApplication.java:2139)
at
er.extensions.appserver.ERXApplication.dispatchRequest(ERXApplication.java:2104)
at
com.webobjects.appserver._private.WOWorkerThread.runOnce(WOWorkerThread.java:144)
at
com.webobjects.appserver._private.WOWorkerThread.run(WOWorkerThread.java:226)
at java.lang.Thread.run(Thread.java:680)
Locked ownable synchronizers:
- <20ce7bbc0> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
Now, ERXApplication.restoreSessionWithID contains an interesting call to
useSessionStoreDeadlockDetection(), but this detection only works in single
threaded mode. I'm afraid I can't afford to switch off concurrent requests even
for a testing period in production.
I'm looking for someone with experience regarding this problem. The doc for
that method mentions that it could help "to find cases when a session is
checked out twice in a single RR-loop, which will lead to a session store
lockup." Since I cannot switch on this detection, what in your experience could
lead to that happening?
Thanks
Maik
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