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Date: Fri, 24 Nov 2006 08:04:03 -0800 (PST)
From: "Phil Steitz (JIRA)" <jira@apache.org>
To: commons-dev@jakarta.apache.org
Subject: [jira] Commented: (DBCP-65) [dbcp] Deadlock when evicting dbcp
 objects (testWhileIdle=true)
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    [ http://issues.apache.org/jira/browse/DBCP-65?page=comments#action_12452488 ] 
            
Phil Steitz commented on DBCP-65:
---------------------------------

I am +1 on option 2, or just migrate to Pool 2 when it is released.  Having spent many hours trying to find workarounds for this and DBCP-44 (trying to do things like 1 outside of [pool], which is hopeless), I agree that the current evictor setup is a recipe for deadlocks and can't be fixed without changes to [pool] or [dbcp] config semantics.

> [dbcp] Deadlock when evicting dbcp objects (testWhileIdle=true)
> ---------------------------------------------------------------
>
>                 Key: DBCP-65
>                 URL: http://issues.apache.org/jira/browse/DBCP-65
>             Project: Commons Dbcp
>          Issue Type: Bug
>         Environment: Operating System: All
> Platform: All
>            Reporter: Wang Xianzhu
>             Fix For: 1.3
>
>
> 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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