Let's hear from others before we put anything on the roadmap. I recall Brian mentioning his need for locks, but AFAIR not in conjunction with JBossCache but with Farming... Manik Surtani wrote: > > On 20 Mar 2009, at 08:36, Bela Ban wrote: > >> I know, but what he wants to do is >> #1 Read a value >> #2 Based on that value (which I assume shouldn't change from >> underneath him), do some computations >> #3 Write the changed value back >> >> I guess the problem is that some other TX could change the value >> and have the later TX fail & roll back... >> >> AFAIR we don't have Cache.lock(K) and unlock(K), do we ? If so, >> would it make sense to add them ? And then we'd have to think about > > We don't at the moment. Adding them is simple, making them scale/ > perform well is hard. :-) > > It would be a simple LockCommand which is broadcast (anycast?) via > RPC. If it doesn't return (in time), assume we don't have the lock > and throw a timeout exception. This call would *have* to be > synchronous though, it can't work in an async manner. > >> * how this fares with TX-incurred locking > > It would hold the locks until unlock() is called, or a tx > completes, whichever happens first, I guess. > >> >> * what type of locks lock() acquires > > Write locks. We don't have such a thing as read locks in Horizon > or even JBC3's MVCC. > >> WDYT ? > > I don't mind putting it on the Horizon roadmap, but I can't promise > when it would get done - its just a case of prioritising stuff. If > another resource is looking unlikely/delayed we have a lot of stuff > on our plate... :-( > >> >> >> >> Manik Surtani wrote: >>> No, a tx +RR is still optimistic cluster-wide in that it is only >>> on tx commit (tx prepare, actually) that remote locks are acquired. >>> >>> This essentially is a distributed lock. >>> >>> >>> On 20 Mar 2009, at 07:34, Bela Ban wrote: >>> >>>> Do we have a hard-lock mechanism like the one below for >>>> Coherence ? >>>> >>>> Would a TX with RR be the equivalent ? >>>> >>>> >>>> -------- Original Message -------- >>>> Subject: RE: [javagroups-users] Distributed Lock Manager >>>> Listener >>>> Date: Thu, 19 Mar 2009 12:03:42 -0500 >>>> From: Urciolo, Kevin J (IS) <Kevin.Urciolo(a)ngc.com&gt; >>>> To: Bela Ban <belaban(a)yahoo.com&gt; >>>> CC: <javagroups-users(a)lists.sourceforge.net&gt; >>>> References: <0E36CF63779A934D876C5E7FD29E74EB01FA4FFC(a)XMBIL123.northgrum.com >>>> > <49C206DC.8030608(a)yahoo.com&gt; >>>> >>>> >>>> >>>> I am trying to accomplish the locking mechanism as shown in this >>>> example >>>> from Coherence. I need to execute a piece of code that is >>>> mutually >>>> exclusive throughout the group. >>>> >>>> I looked at the VotingAdapter. I seemed to get the >>>> notifications before >>>> the lock was released, but caused the thread waiting for the >>>> lock to try >>>> again too early and get another LockNotGrantedException. >>>> >>>> NamedCache cache = CacheFactory.getCache("dist-cache"); >>>> Object key = "example_key"; >>>> cache.lock(key, -1); >>>> try >>>> { >>>> Object value = cache.get(key); >>>> // application logic >>>> cache.put(key, value); >>>> } >>>> finally >>>> { >>>> // Always unlock in a "finally" block >>>> // to ensure that uncaught exceptions >>>> // don't leave data locked >>>> cache.unlock(key); >>>> } >>>> -----Original Message----- >>>> From: Bela Ban [mailto:belaban@yahoo.com] Sent: Thursday, March >>>> 19, 2009 4:48 AM >>>> To: Urciolo, Kevin J (IS) >>>> Cc: javagroups-users(a)lists.sourceforge.net >>>> Subject: Re: [javagroups-users] Distributed Lock Manager Listener >>>> >>>> >>>> >>>> Urciolo, Kevin J (IS) wrote: >>>>> I would like to use the distributed lock manager. However, I >>>>> would like my components to block until a lock is available >>>>> instead of getting an exception thrown. >>>> >>>> What if the lock cannot be granted ? There's a >>>> LockNotGrantedException >>>> when this happens. I also assume you would not want to wait >>>> forever if a >>>> lock is held by a different owner. >>>> >>>>> Is this possible? If not, is it possible to listen for events >>>>> on locks >>>> >>>>> so I can implement my own listener mechanism? >>>> >>>> There's a VotingAdapter class which implements >>>> VoteResponseProcessor. This class has callbacks, but of course >>>> you could also write your own >>>> implementation >>>> >>>> -- >>>> Bela Ban >>>> Lead JGroups / Clustering Team >>>> JBoss - a division of Red Hat >>>> >>>> >>>> >>>> >>>> -- >>>> Bela Ban >>>> Lead JGroups / Clustering Team >>>> JBoss - a division of Red Hat >>>> >>>> >>> >>> -- >>> Manik Surtani >>> Lead, JBoss Cache >>> http://www.jbosscache.org >>> manik(a)jboss.org >>> >>> >>> >>> >>> >> >> -- >> Bela Ban >> Lead JGroups / Clustering Team >> JBoss - a division of Red Hat >> > > -- > Manik Surtani > Lead, JBoss Cache > http://www.jbosscache.org > manik(a)jboss.org > > > > > -- Bela Ban Lead JGroups / Clustering Team JBoss - a division of Red Hat