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From Daniel John Debrunner <...@apache.org>
Subject Re: security manager implication of requiring one or multiple system properties?
Date Sat, 28 Jan 2006 23:54:48 GMT
Mike Matrigali wrote:

> Note that the problem we are trying to solve is multiple derby
> instances from 2 classloaders accessing the same database at the
> same time.  We are unlikely to ever allow this - as correct
> direct access to the database requires sharing a lot of information
> (page cache, lock tables, ...).
> 
> I am not happy with the system property approach - but best I could
> come up with so far, and the thread describes the problems with current
> lock files.
> 
> I don't know much about what is and is not available from different
> classloaders.  I think all that is needed is some way to generate a
> unique key which can be used to identify what jvm instance I am in.  The
> pid
> of the jvm would work, but I don't think it is available from java.
> Then each classloader in the jvm could use some sort of file lock to
> tell if another classloader in the same jvm existed.

I guess I'm not seeing the jump from unique jvm id to use of a file
lock. If a file lock doesn't prevent multiple threads within a JVM from
modifying a file, how does the unique jvm id help?

Dan.



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