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From "craig mcmillan (JIRA)" <j...@apache.org>
Subject [jira] Created: (DBCP-281) CLONE -[dbcp] Deadlock when evicting dbcp objects (testWhileIdle=true)
Date Mon, 26 Jan 2009 13:59:59 GMT
CLONE -[dbcp] Deadlock when evicting dbcp objects (testWhileIdle=true)
----------------------------------------------------------------------

                 Key: DBCP-281
                 URL: https://issues.apache.org/jira/browse/DBCP-281
             Project: Commons Dbcp
          Issue Type: Bug
         Environment: Operating System: All
Platform: All
            Reporter: craig mcmillan
             Fix For: 1.2.2


The GenericKeyedObjectPool$Evictor thread has probability of deadlock with dbcp
objects.

For example, at a certain time, a normal user thread calls a PoolingConnection
object's synchronized method, which in turn calls GenericKeyedObjectPool
object's synchronzied method.

At the same time, the evictor thread calls the GenericKeyedObjectPool object's
synchronized method 'evict', which in turn calls the PoolingConnection object's
synchronized method.  When testWhileIdle=true, the probability of evictor
calling GenericKeyedObjectPool's synchronized method is much greater.

The following is the deadlock information in the thread dump of our program
(testWhileIdle=true):

"Thread-106":
	at org.apache.commons.dbcp.AbandonedTrace.removeTrace(AbandonedTrace.java:221)
	- waiting to lock <0x6a6b1b80> (a org.apache.commons.dbcp.PoolingConnection)
	at
org.apache.commons.dbcp.PoolablePreparedStatement.passivate(PoolablePreparedStatement.java:100)
	at
org.apache.commons.dbcp.PoolingConnection.passivateObject(PoolingConnection.java:239)
	at
org.apache.commons.pool.impl.GenericKeyedObjectPool.evict(GenericKeyedObjectPool.java:1001)
	- locked <0x6a6b1858> (a org.apache.commons.pool.impl.GenericKeyedObjectPool)
	at
org.apache.commons.pool.impl.GenericKeyedObjectPool$Evictor.run(GenericKeyedObjectPool.java:1156)
	at java.lang.Thread.run(Thread.java:534)
"Thread-41":
	at
org.apache.commons.pool.impl.GenericKeyedObjectPool.borrowObject(GenericKeyedObjectPool.java:715)
	- waiting to lock <0x6a6b1858> (a
org.apache.commons.pool.impl.GenericKeyedObjectPool)
	at
org.apache.commons.dbcp.PoolingConnection.prepareStatement(PoolingConnection.java:87)
	- locked <0x6a6b1b80> (a org.apache.commons.dbcp.PoolingConnection)
	at
org.apache.commons.dbcp.DelegatingConnection.prepareStatement(DelegatingConnection.java:185)
	at
org.apache.commons.dbcp.PoolingDataSource$PoolGuardConnectionWrapper.prepareStatement(PoolingDataSource.java:278)
...

This problem can be worked around by setting testWhileIdle to false, although
there is still very small possibility of deadlock.

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