[jira] Updated: (DERBY-3612) Developer's Guide needs correction on garbage collection

["Kim Haase (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/DERBY-3612?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Kim Haase updated DERBY-3612:
-----------------------------

    Attachment: tdevdvlp20349.html
                DERBY-3612.diff

Attaching DERBY-3612.diff and tdevdvlp20349.html. This patch 

 - corrects the description of System.gc() to make clear that it requests but does not force garbage collection

 - removes the references to the -nogc and -noclassgc options, since these appear to have been obsolete since Java 2 came in, and replaces them with the current non-standard -Xnoclassgc option. 

 - tidies up the language a bit (changes passive voice to active, etc.)

I'd be grateful if someone could check the correctness of the modified info. If I don't hear in a week or so, though, I'll go ahead and commit this.

> 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: 10.3.2.1
>            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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