Re: [infinispan-dev] Semaphore vs Lock

On Tue, Mar 13, 2012 at 2:53 PM, Galder Zamarreño <galder(a)redhat.com&gt; wrote: > > On Mar 8, 2012, at 12:42 PM, Dan Berindei wrote: > >> On Wed, Mar 7, 2012 at 2:39 PM, Sanne Grinovero <sanne(a)infinispan.org&gt; wrote: >>> On 7 March 2012 12:05, Galder Zamarreño <galder.zamarreno(a)redhat.com&gt; wrote: >>>> Hi, >>>> >>>> I was reading up about Java's Semaphores (http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/Semaphore.html) and a couple of ideas came to my mind: >>>> >>>> 1. Wouldn't it make sense to use binary semaphores instead of locks in Infinispan? We're already having to override ReentrantLock in order to have locks owned by Transactions rather than threads. Initially I thought it might make easier for deadlock detection, but not so sure right now cos we're already changing things to avoid thread ownership of locks. >>>> >> >> We don't support most of the Lock operations, so I think it would be >> fair to remove 'implements Lock' from the OwnableReentrantLock >> declaration. But we can't remove the reentrant part, as we acquire the >> lock when we put a value in L1 in DistributionInterceptor - after we >> have already acquired the lock once in LockInterceptor (that's before >> we even consider a pessimistic transaction doing multiple puts on the >> same key). > > True, but reentrant is only needed for non-transactional scenarios. For pessimistric transactions, we have ownable locks where they're owned by transactions. > I meant reentrant in a more general sense - OwnableReentrantLock is reentrant because it allows the same transaction to lock the same key twice, even if it happens on different threads.