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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-2689) Deadlock with GenericPreparedStatement
Date Tue, 26 Jun 2007 22:13:26 GMT

    [ https://issues.apache.org/jira/browse/DERBY-2689?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12508349
] 

Knut Anders Hatlen commented on DERBY-2689:
-------------------------------------------

> For 1, there seems to be no synchronization at all in this class.

Yes, you're absolutely right. For some reason I kept thinking that it was shared between threads,
but lcc is not.

> As far as 2 goes-- if we set "unusedActs" to false at the beginning of the loop and while
trying to close all activations, get an exception won't we end up with the case where unusedActs
= false, yet there are unused activations which the loop did not get to?

I think you are right. We risk ending up with an incorrect value no matter where we put the
assignment. Since it's really just a hint as to when it could be worthwhile to do the cleanup,
I don't think it really matters. If we are leaking activations, the cleanup code will be triggered
sooner or later, but there might be more than 20 activations (which is a low number anyway).

> On the same note, I'm not sure I understand why we have to do the following:
>
> for (int i = acts.size() - 1; i >= 0; i--) {
>
> // it maybe the case that a reset() ends up closing
> // one or more activation leaving our index beyond
> // the end of the array
> if (i >= acts.size())
> continue;

BaseActivation.close(), which is called further down in the method, calls lcc.removeActivation()
which removes only one activation and should therefore not cause any problems. I assume that
the reset() method mentioned in the comment is BaseActivation.reset(), but I can't see that
it will close any activations, so I believe you are right on this too. Perhaps the comment
refers to some old code?

> Deadlock with GenericPreparedStatement
> --------------------------------------
>
>                 Key: DERBY-2689
>                 URL: https://issues.apache.org/jira/browse/DERBY-2689
>             Project: Derby
>          Issue Type: Bug
>          Components: JDBC
>    Affects Versions: 10.2.2.0
>         Environment: Windows
>            Reporter: Marc Ewert
>            Assignee: Manish Khettry
>            Priority: Critical
>         Attachments: deadlock.patch.txt, TestDerbyPreparedStatements.java
>
>
> We encountered two times a deadlock inside of derby. It seems that we can't workaround
it. The involved two threads are attached, it looks like a classical deadlock:
> "Thread-22" daemon prio=6 tid=0x0cdaa400 nid=0x1c0 waiting for monitor entry [0x1317f000..0x1317fd4c]
>    java.lang.Thread.State: BLOCKED (on object monitor)
> 	at org.apache.derby.impl.sql.GenericPreparedStatement.finish(Unknown Source)
> 	- waiting to lock <0x052f4d70> (a org.apache.derby.impl.sql.GenericPreparedStatement)
> 	at org.apache.derby.impl.sql.execute.BaseActivation.close(Unknown Source)
> 	at org.apache.derby.impl.sql.conn.GenericLanguageConnectionContext.addActivation(Unknown
Source)
> 	at org.apache.derby.impl.sql.execute.BaseActivation.initFromContext(Unknown Source)
> 	at org.apache.derby.impl.services.reflect.LoadedGeneratedClass.newInstance(Unknown Source)
> 	at org.apache.derby.impl.services.reflect.ReflectGeneratedClass.newInstance(Unknown
Source)
> 	at org.apache.derby.impl.sql.GenericActivationHolder.<init>(Unknown Source)
> 	at org.apache.derby.impl.sql.GenericPreparedStatement.getActivation(Unknown Source)
> 	- locked <0x05306f88> (a org.apache.derby.impl.sql.GenericPreparedStatement)
> 	at org.apache.derby.impl.jdbc.EmbedPreparedStatement.<init>(Unknown Source)
> 	at org.apache.derby.impl.jdbc.EmbedPreparedStatement20.<init>(Unknown Source)
> 	at org.apache.derby.impl.jdbc.EmbedPreparedStatement30.<init>(Unknown Source)
> 	at org.apache.derby.impl.jdbc.EmbedPreparedStatement40.<init>(Unknown Source)
> 	at org.apache.derby.jdbc.Driver40.newEmbedPreparedStatement(Unknown Source)
> 	at org.apache.derby.impl.jdbc.EmbedConnection.prepareStatement(Unknown Source)
> 	- locked <0x047beb00> (a org.apache.derby.impl.jdbc.EmbedConnection40)
> 	at org.apache.derby.impl.jdbc.EmbedConnection.prepareStatement(Unknown Source)
>         [custom methods]
> "ThreadPoolThread-SyncScheduler-3-1" prio=2 tid=0x0e620400 nid=0xfec waiting for monitor
entry [0x10a7e000..0x10a7fa14]
>    java.lang.Thread.State: BLOCKED (on object monitor)
> 	at org.apache.derby.impl.sql.GenericPreparedStatement.finish(Unknown Source)
> 	- waiting to lock <0x05306f88> (a org.apache.derby.impl.sql.GenericPreparedStatement)
> 	at org.apache.derby.impl.sql.execute.BaseActivation.close(Unknown Source)
> 	at org.apache.derby.impl.sql.conn.GenericLanguageConnectionContext.addActivation(Unknown
Source)
> 	at org.apache.derby.impl.sql.execute.BaseActivation.initFromContext(Unknown Source)
> 	at org.apache.derby.impl.services.reflect.LoadedGeneratedClass.newInstance(Unknown Source)
> 	at org.apache.derby.impl.services.reflect.ReflectGeneratedClass.newInstance(Unknown
Source)
> 	at org.apache.derby.impl.sql.GenericActivationHolder.<init>(Unknown Source)
> 	at org.apache.derby.impl.sql.GenericPreparedStatement.getActivation(Unknown Source)
> 	- locked <0x052f4d70> (a org.apache.derby.impl.sql.GenericPreparedStatement)
> 	at org.apache.derby.impl.jdbc.EmbedPreparedStatement.<init>(Unknown Source)
> 	at org.apache.derby.impl.jdbc.EmbedPreparedStatement20.<init>(Unknown Source)
> 	at org.apache.derby.impl.jdbc.EmbedPreparedStatement30.<init>(Unknown Source)
> 	at org.apache.derby.impl.jdbc.EmbedPreparedStatement40.<init>(Unknown Source)
> 	at org.apache.derby.jdbc.Driver40.newEmbedPreparedStatement(Unknown Source)
> 	at org.apache.derby.impl.jdbc.EmbedConnection.prepareStatement(Unknown Source)
> 	- locked <0x04225178> (a org.apache.derby.impl.jdbc.EmbedConnection40)
> 	at org.apache.derby.impl.jdbc.EmbedConnection.prepareStatement(Unknown Source)
>         [custom methods]

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