Inserting single semaphore into the JavaSpace

Hello,

I need to have for certain operations exclusive access to the JavaSpace 
or at least part of it. I found the approach of a distributed semaphore 
in the book from Freeman. So far so good. Now I have the problem that 
this semaphore must only be inserted once into the space. Two or more 
clients might be in a race to be the first one that inserts the semaphore.

GigaSpaces has a write method that you can call with a parameter so that 
an exception is thrown if the entry already exists in the space. 
Unhappily, this is not possible with the JavaSpace05 interface.  I could 
create my own Jini service for this, but  I would prefer a simpler 
solution as I have other things to do. I found the threads "Re: Seeding 
a space with a semaphore" and "Adding a "singleton" method to JavaSpace 
API?" in the mailing archive, but a "cookbook" solution wasn't provided 
there.

What I do at the moment is adding a token with a specific label to an 
RMI registry. Not really a nice solution when you have Jini at your 
disposal anyway, but simple and quick. Any possible race condition is 
then handled by the RMI registry. The guy that comes second in a race to 
register this token with the same label will receive an exception, so 
the token cannot be inserted twice. Any other ideas I was pursuing 
(harcoded seed, and others) always turn out as not working. Maybe 
someone knows a simple solution that works without installing a new Jini 
service.

Thanks, Oliver Plohmann

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