Java uses a modified CLH lock queue to implement fair semaphores:
https://github.com/openjdk/jdk/blob/jdk-9%2B102/jdk/src/java.base/share/classes/java/util/concurrent/Semaphore.java#L172
https://github.com/openjdk/jdk/blob/jdk-9%2B102/jdk/src/java.base/share/classes/java/util/concurrent/locks/AbstractQueuedSynchronizer.java

This could be more performant than our current implementation that uses a mutex on top of a queue.