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From "Daniel John Debrunner (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-700) Derby does not prevent dual boot of database from different classloaders on Linux
Date Thu, 14 Jun 2007 13:42:26 GMT

    [ https://issues.apache.org/jira/browse/DERBY-700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12504735
] 

Daniel John Debrunner commented on DERBY-700:
---------------------------------------------

Couple of minor additonal comments:

 - The code would be a little simpler if getJvmId() just returned a String instead of a UUID.
Then there's no need to convert
    the value read back from disk to a uuid. String's compare just as well as UUIDs for this
purpose.

- The reading of the on-disk identifier has this code:

+            try 
+            {
+                if (exFileLock.length() != 0)
+                    onDiskJvmId = uuidFactory.recreateUUID(lckFileRaf.readUTF());
+            }   
+            catch (Exception e)
+            {
+                // The previous owner of the lock may have died before we
+                // finish writing its UUID down. Assume uuid file is invalid
+                // Set the id on the disk to null value.
+                onDiskJvmId = null;
+            }


  - Why is the file length of zero special cased?

  - I think the comment could be improved to

+                // The previous owner of the lock may have died before we
+                // finish writing its UUID down. Assume uuid file is invalid
+                // and thus the database is not in use (locked).

  

> Derby does not prevent dual boot of database from different classloaders on Linux
> ---------------------------------------------------------------------------------
>
>                 Key: DERBY-700
>                 URL: https://issues.apache.org/jira/browse/DERBY-700
>             Project: Derby
>          Issue Type: Bug
>          Components: Store
>    Affects Versions: 10.1.2.1
>         Environment: ava -version
> java version "1.4.2_08"
> Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_08-b03)
> Java HotSpot(TM) Client VM (build 1.4.2_08-b03, mixed mode)
>            Reporter: Kathey Marsden
>            Assignee: Kathey Marsden
>            Priority: Critical
>             Fix For: 10.3.0.0
>
>         Attachments: DERBY-700.diff, DERBY-700.stat, derby-700_06_07_07_diff.txt, derby-700_06_07_07_stat.txt,
derby-700_diff.txt, derby-700_stat.txt, DERBY-700_v1_use_to_run_DualBootrepro_multithreaded.diff,
DERBY-700_v1_use_to_run_DualBootrepro_multithreaded.stat, derby-700_with_NPE_fix_diff.txt,
derby-700_with_NPE_fix_stat.txt, derby.log, derby700_singleproperty_v1.diff, derby700_singleproperty_v1.stat,
DualBootRepro.java, DualBootRepro2.zip, DualBootRepro_mutltithreaded.tar.bz2, releaseNote.html
>
>
> Derby does not prevent dual boot from two different classloaders on Linux.
> To reproduce run the  program DualBootRepro with no derby jars in your classpath. The
program assumes derby.jar is in 10.1.2.1/derby.jar, you can change the location by changing
the DERBY_LIB_DIR variable.
> On Linux the output is:
> $java -cp . DualBootRepro
> Loading derby from file:10.1.2.1/derby.jar
> 10.1.2.1/derby.jar
> Booted database in loader java.net.URLClassLoader@8ed465
> FAIL: Booted database in 2nd loader java.net.URLClassLoader@dc6a77
> On Windows I get the expected output.
> $ java -cp . DualBootRepro
> Loading derby from file:10.1.2.1/derby.jar
> 10.1.2.1/derby.jar
> Booted database in loader java.net.URLClassLoader@1ac04e8
> PASS: Expected exception for dualboot:Another instance of Derby may have already booted
the database D:\marsden\repro\dualboot\mydb.

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