Developer's Guide needs correction on garbage collection
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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
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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