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Editorial Team
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Asked: 2026-06-14T00:32:03+00:00

I am using C3p0 connection pool and I am observing following exception in my

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I am using C3p0 connection pool and I am observing following exception in my server. 

 com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector@ed866f -- APPARENT DEADLOCK!!! Complete Status:
    Managed Threads: 1
    Active Threads: 1
    Active Tasks:
        com.mchange.v2.resourcepool.BasicResourcePool$1DestroyResourceTask@995ec2 (com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0)
    Pending Tasks: 
            com.mchange.v2.resourcepool.BasicResourcePool$1RefurbishCheckinResourceTask@11c3ceb
            com.mchange.v2.resourcepool.BasicResourcePool$1RefurbishCheckinResourceTask@e392ed
            com.mchange.v2.resourcepool.BasicResourcePool$1RefurbishCheckinResourceTask@c33853
            com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@a6f77d
            com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@1c25bfc
            com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@12534a9
            com.mchange.v2.resourcepool.BasicResourcePool$1RefurbishCheckinResourceTask@1a4564c
Pool thread stack traces:
        Thread[com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0,5,main]
                oracle.jdbc.driver.OracleStatement.close(OracleStatement.java:1338)
                com.mchange.v2.c3p0.impl.NewPooledConnection.cleanupUncachedStatements(NewPooledConnection.java:651)
                com.mchange.v2.c3p0.impl.NewPooledConnection.close(NewPooledConnection.java:539)
                com.mchange.v2.c3p0.impl.NewPooledConnection.close(NewPooledConnection.java:234)
                com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.destroyResource(C3P0PooledConnectionPool.java:470)
                com.mchange.v2.resourcepool.BasicResourcePool$1DestroyResourceTask.run(BasicResourcePool.java:964)
               com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)

My configuration is

<property name="initialPoolSize" value="1" />
    <property name="minPoolSize" value="1" />
    <property name="maxPoolSize" value="20" />
    <property name="maxIdleTime" value="240" />
    <property name="checkoutTimeout" value="60000" />
    <property name="acquireRetryAttempts" value="0" />
    <property name="acquireRetryDelay" value="1000" />
    <property name="debugUnreturnedConnectionStackTraces" value="true" />
    <property name="unreturnedConnectionTimeout" value="300" />
    <property name="numHelperThreads" value="1" />
    <property name="preferredTestQuery" value="SELECT 1 FROM DUAL" />

After some googing I found following threads.
https://forum.hibernate.org/viewtopic.php?t=947246

It is suggested to disable the statement caching to avoid this problem. But in my configuration I didn’t enable the statement caching(maxStatements, maxStatementsPerConnection are 0 by default).

Please suggest any alternatives.

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1 Answer

  1. Editorial Team

    Don’t set numHelperThreads to 1.

    If you set numHelperThreads to 1, any slow task will trigger an APPARENT DEADLOCK. c3p0 relies on an internal Thread pool. One thread does not make a pool. Let numHelperThreads have at least its default value of 3.

    Specifically what is going on in your stack trace is that an attempt by the Connection pool to close() a Connection is taking long time, for some reason. There could be a real problem here, if this happens a lot, but it could just be an occasional slow operation, which a reasonably sized Thread pool would just handle and shrug off.

    Good luck!

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