Author: manik.surtani(a)jboss.com Date: 2009-03-19 06:06:23 -0400 (Thu, 19 Mar 2009) New Revision: 7921 Modified: core/branches/flat/src/main/java/org/horizon/util/concurrent/locks/containers/AbstractPerEntryLockContainer.java Log: HORIZON-40 - Create a lock-per-entry lock manager Modified: core/branches/flat/src/main/java/org/horizon/util/concurrent/locks/containers/AbstractPerEntryLockContainer.java =================================================================== --- core/branches/flat/src/main/java/org/horizon/util/concurrent/locks/containers/AbstractPerEntryLockContainer.java 2009-03-19 09:59:50 UTC (rev 7920) +++ core/branches/flat/src/main/java/org/horizon/util/concurrent/locks/containers/AbstractPerEntryLockContainer.java 2009-03-19 10:06:23 UTC (rev 7921) @@ -17,11 +17,14 @@ protected abstract Lock newLock(); - public Lock getLock(Object key) { - Lock l = newLock(); - Lock tmp = locks.putIfAbsent(key, l); - if (tmp != null) l = tmp; - return l; + public final Lock getLock(Object key) { + // this is an optimisation. It is not foolproof as we may still be creating new locks unnecessarily (thrown away + // when we do a putIfAbsent) but it minimises the chances somewhat, for the cost of an extra CHM get. + Lock lock = locks.get(key); + if (lock == null) lock = newLock(); + Lock existingLock = locks.putIfAbsent(key, lock); + if (existingLock != null) lock = existingLock; + return lock; } public int getNumLocksHeld() { @@ -33,13 +36,23 @@ } public boolean acquireLock(Object key, long timeout, TimeUnit unit) throws InterruptedException { - Lock l = getLock(key); - boolean success = l.tryLock(timeout, unit); - if (l != locks.get(key)) { - l.unlock(); - success = acquireLock(key, timeout, unit); // todo avoid recursion here, this could get ugly! + while (true) { + Lock lock = getLock(key); + if (lock.tryLock(timeout, unit)) { + // lock acquired. Now check if it is the *correct* lock! + Lock existingLock = locks.putIfAbsent(key, lock); + if (existingLock != null && existingLock != lock) { + // we have the wrong lock! Unlock and retry. + lock.unlock(); + } else { + // we got the right lock. + return true; + } + } else { + // we couldn't acquire the lock within the timeout period + return false; + } } - return success; } public void releaseLock(Object key) {