Which implementations of Condition do not require current thread to hold the lock?

I'm not aware of any Condition implementation in the JDK that allows waiting or signaling without owning the monitor at the same time.

Practically all of the java.util.concurrent classes rely on AbstractQueuedSynchronizer which establishes the same contract as the built-in monitor methods wait()/notify()/notifyAll() for the condition variables it provides, i.e. it requires owning the internal lock in order to allow calling await()/signal()/signalAll().

If you try a simple example using the proposed FifoReadWriteLock, you'll find that it spews a serious amount of IllegalMonitorStateExceptions courtesy of its writeUnlock() method. These exceptions disappear if you apply the lock-try-finally approach from the other methods.

While indeed owning the monitor is not absolutely required to wait or signal, often it's the preferable approach, as it saves you from racy condition reads, it shouldn't be too costly as the hand-off between the internal wait sets of the same monitor can still be done fairly efficiently, and because most often you need it for both signaling and scheduling instead of just signaling.