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From Daniel John Debrunner <...@apache.org>
Subject Re: security manager implication of requiring one or multiple system properties?
Date Sun, 29 Jan 2006 00:10:51 GMT
Daniel John Debrunner wrote:

> 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?

Sorry, found the discussion of the possible algorithm at

http://mail-archives.apache.org/mod_mbox/db-derby-dev/200601.mbox/%3c43D68A01.5050806@sbcglobal.net%3e

Dan.


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