Why Locks are Serializable in java?

Question

One question arised in my mind while looking into the implementation of the ReentrantLock class. ReentrantLock is serializable and in the documentation it says that any deserialized lock is always unlocked irrespective of the state when it was serialized. This make sense because the state Lock and unlock is basically based on the threads at the runtime (who hold the lock) and while we de-serialize those threads may not be available.

Question is : Why we need the Lock to persist because it does not store it’s basic state (locked/unlocked) ? Right now I can assume that may be for the fairness property of the lock. But fairness is again depending on the underlying OS so if we persists the lock on one platform and deserialized on another because (write once and run anywhere) it may not work so no point in persisting only for fairness.

Hope I clearly put my confusion about Lock serialization in java.

Answer 1

http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/locks/Condition.html http://download.java.net/jdk7/archive/b123/docs/api/java/util/concurrent/locks/ReentrantLock.html

I would say that the reason why Lock persists is so that you're able to serialize objects that depend on Lock itself. If Lock wasn't serializable, anything dependent on it wouldn't be able to be serialized either.

You'd also be able to store the owner, holdCount, queuedThreads and all of the other stuff that you can see on the API page that I linked above for ReentrantLock.