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From "Kim Haase (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3612) Developer's Guide needs correction on garbage collection
Date Thu, 17 Apr 2008 21:13:21 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3612?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12590205#action_12590205

Kim Haase commented on DERBY-3612:

Thanks, Martin. I hope we can get an answer to this question. I tried removing a System.gc()
call from one of my programs for DERBY-3200, which starts Derby in embedded mode, stops it,
restarts it, then stops it again. I removed the System.gc() call from between the stop and
restart. There seems to be no change in behavior. But this is a fairly trivial example.

> Developer's Guide needs correction on garbage collection
> --------------------------------------------------------
>                 Key: DERBY-3612
>                 URL: https://issues.apache.org/jira/browse/DERBY-3612
>             Project: Derby
>          Issue Type: Bug
>          Components: Documentation
>    Affects Versions:
>            Reporter: Kim Haase
>            Assignee: Kim Haase
>            Priority: Minor
>         Attachments: DERBY-3612.diff, tdevdvlp20349.html
> In a comment on DERBY-3585, Martin Zaun pointed out the following error:
> devguide/tdevdvlp20349.dita
>    - found a flatly wrong statement but did NOT correct here since
>      unrelated to server shutdown authentication:
>      "You cannot explicitly request that the JVM unload a class, but you
>      can ensure that the EmbeddedDriver class is unloaded by using a
>      System.gc() to force it to garbage collect classes that are no longer
>      needed. Running with -nogc or -noclassgc definitely prevents the class
>      from being unloaded and makes you unable to restart Derby in the same
>      JVM."
>      System.gc() is only a suggestion to the Runtime to garbage-collect, it
>      cannot be enforced, and there's no guarantee whatsoever that GC has
>      run and any classes been unloaded. Likewise it's most probably not
>      guarantueed that -nogc or -noclassgc definitely (!) prevent a class
>      from being unloaded (a JVM may ignore these options...) 
> This needs to be fixed. Thanks, Martin.
> One more question: are -nogc and -noclassgc java command line options, or options to
some other command? I can't find them in the java command documentation -- http://java.sun.com/javase/6/docs/technotes/tools/windows/java.html.
There is an -Xnoclassgc option, however.

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