Hello, I've spoken with Manik in IRC about this, so wanted to share this, especially because he mentioned to ask someone to help me. I've been busy writing a lock-stress-test for our implementation for Lucene's Lock and Lockfactory, and got some trouble using cache.putIfAbsent(Object key, Object value); It appears to not behave atomically as it should. I've confirmed the test is working when mocking the cache with a plain ConcurrentHashMap, so next step for me is having someone with better knowledge of Infinispan core have a look into the code; I might have some configuration problem. My test is attached to ISPN-227, here are some instructions: the test to run is org.infinispan.lucene.InfinispanLockFactoryStressTest, which creates and uses several org.infinispan.lucene.InfinispanLock. mvn test -Dtest=org.infinispan.lucene.InfinispanLockFactoryStressTest -Dbind.address=127.0.0.1 -Djava.net.preferIPv4Stack=true The test defines 3 different cacheFactory, only one is not commented, so please edit the code to try against a different ConcurrentMap implementation and see what happens. Some status will be sent to system.out. * MultiNodeTestCacheFactory emulates different nodes sharing state, and each node is having n threads (using Core Infinispan's MultipleCacheManagersTest) * ConcurrentHashMapCacheTestFactory uses Java's ConcurrentHashMap * LocalISPNCacheTestFactory (using TestCacheManagerFactory.createLocalCacheManager(false)) This is not intended to be committed for now, just to find out what's wrong. Also this is not the Lock implementation as we need it, but first this step should be fixed. thanks, Sanne