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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 13:57:26 GMT

    [ https://issues.apache.org/jira/browse/DERBY-2689?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12508180
] 

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

Hi Manish,

Thank you for working on this issue. I looked at the patch and I have a couple of questions/comments:

1) Since GenericLanguageConnectionContext.acts now is an unsynchronized ArrayList and not
a Vector, is it safe to access/modify it outside the synchronized block?

2) I noticed that you moved "unusedActs = false;" below the loop. I believe that the assignment
was placed above the loop deliberately (see Dan's comment 25/Aug/06 on DERBY-418).

3) There are some lines >80 characters.

4) Most of the changes in GenericLanguageConnectionContext are pure whitespace changes (adding
or removal of trailing blanks). Also, some extra garbage has ended up in the comments, like
"// size exceeds 20.SelectNod3" and "(...) true *if*z *all* (...)"

5) *Tiny* nit: In GenericPreparedStatement.getActivation(), ac is initialized to null. Since
this initial value is not intended to be used, I think it is better to leave the variable
uninitialized. The compiler will complain if one tries to use an uninitialized variable, so
by setting it to null we actually remove some compile-time error checking.

> 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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