Re: Inserting single semaphore into the JavaSpace

You said without another service...  Dan Creswell has a distributed lock =
manager=20
on his web site that works.  I have one as well that is a little differen=
t in=20
design, using Jeri for communications instead jgroups.  But, in the end, =
its=20
something that is generally useful.   I had some thoughts about how to do=
 this=20
using Javaspaces, but have never had a chance to explore the ideas to see=
 if=20
they'd work.

Gregg Wonderly

Oliver Plohmann wrote:
> Hello,
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> thanks for the link. The article explains the idea of a token used as a=
=20
> semaphore. This is what I saw in Freeman's book and that's how I intend=
=20
> to do synchronization. Problem is that someone must be the first one to=
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> insert the >single< semaphore entry into the space since it is empty to=
=20
> begin with. Now there might be several clients using the space and ther=
e=20
> must be one of them who will insert the initial semaphore. How do they=20
> agree on who will do this when an initial semaphore not yet exists in=20
> the space to prevent race conditions from happening when working out th=
e=20
> agreement who will be the one?
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> As explained I use the RMI registry as a workaround to determine who is=
=20
> the first one (everyone that comes second faces a AlreadyExistsExceptio=
n=20
> when binding a remote object to the registry that already exists there=20
> with the same name) and thus is allowed to write the initial semaphore=20
> to the space.
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> I feel a method like
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> writeOnce(Entry entry, Transaction trx, long timeout) throws=20
> EntryAlreadyExistsException
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> would be a nice thing to have in the JavaSpace interface. Many=20
> concurrency issues could be solved easily this way and efficiently.=20
> Maybe there is still someone who has had this problem as well and found=
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> a simple quick solution.
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> Thanks, Oliver Plohmann
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> Holger Hoffst=E4tte wrote:
>> Oliver Plohmann wrote:
>> =20
>>> I need to have for certain operations exclusive access to the JavaSpa=
ce
>>> or at least part of it. [..]
>>>    =20
>>
>> There is a "discussion" with a pointer to an article on TSS:
>> http://www.theserverside.com/common/printthread.tss?thread_id=3D45418
>>
>> This should do what you want.
>>
>> -h
>>
>> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
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=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=20
>>
>> To unsubscribe, send email to [email protected] and include in the=
=20
>> body
>> of the message "signoff JAVASPACES-USERS".  For general help, send=20
>> email to
>> [email protected] and include in the body of the message "help".
>>
>> To view past JAVASPACES-USERS postings, please see:
>> http://archives.java.sun.com/archives/javaspaces-users.html
>>
>>  =20
>=20

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
To unsubscribe, send email to [email protected] and include in the bo=
dy
of the message "signoff JAVASPACES-USERS".  For general help, send email =
to
[email protected] and include in the body of the message "help".

To view past JAVASPACES-USERS postings, please see:
http://archives.java.sun.com/archives/javaspaces-users.html