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From Paul Taylor <paul_t...@fastmail.fm>
Subject Re: Best way to detect if embedded derby is being used by another application ?
Date Wed, 03 Feb 2010 11:22:25 GMT
Dag H. Wanvik wrote:
> Paul Taylor <paul_t100@fastmail.fm> writes:
>
>   
>> Hi, I'm trying to prevent a program being run concurrently by trying
>> to access the database but getting in a bit of a mess, what is the
>> simplest/neated way of doing this.
>>     
>
> Normally (al least newer Derby releases), if you try to connect
> (implied boot) a Derby database which has already been booted by
> another VM you would get an error message. You could also check for
> the presence of the db.lck file in the database's directory before you
> attempt to boot a database.
>
>   /export/home/tmp/derby/sb/sb1/wombat:
>   :
>   -rw-r--r--   1 user group       38 feb.  2 15:30 db.lck   <------- 
>   -rw-r--r--   1 user group        4 feb.  2 15:30 dbex.lck
>   drwxr-xr-x   2 user group      512 feb.  2 15:30 log
>   drwxr-xr-x   2 user group     1536 feb.  2 15:30 seg0
>   -rw-r--r--   1 user group      860 feb.  2 15:30 service.properties
>   drwxr-xr-x   2 user group      512 feb.  2 15:30 tmp
>
> On a normal shutdown this file will be removed. An abnormal
> termination would leave the lock file in place, though, so that needs
> to be considered before you decide if that's a sufficient hint for
> your needs, since you could then risk starving the waiting VM..
>
> Dag
>
>   
 I thought if there was an abnormal termination then the db.lck is left 
in place and an attempt to boot the db will fail., and this wast he crux 
of my problem , my code is 99% Java but there is 1% native code provided 
by a 3rd party that I have to call using Runtime that does crash 
occasionally. But I've just tried starting my application , making 
copies of db.lck and db.ex.lck and the starting the program again and it 
actually starts okay.

But in the real world I get users complaining that they cannot start the 
program because it complains the program is already running, even though 
it isnt, any ideas.

Paul

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