ConcurrentLinkedDeque vs LinkedBlockingDeque

Question

I need to have a thread-safe LIFO structure and found that I can use thread-safe implementations of Deque for this. Java 7 has introduced ConcurrentLinkedDeque and

Answer 1

Two things:

1: If I were to use only the non-blocking methods in LinkedBlockingDeque such as addFirst() and removeFirst() does it have any difference to ConcurrentLinkedDeque?

These methods do have difference in terms of concurrent locking behavior, in LinkedBlockingDeque:

public E removeFirst() {
        E x = pollFirst();
        ..
    }
 public E pollFirst() {
        lock.lock(); //Common lock for while list
        try {
            return unlinkFirst();
        } finally {
            lock.unlock();
        }
    }

Similarly for addFirst method. In ConcurrentLinkedDeque this locking behavior for both the method is different and is more efficient as it doesn't lock the whole list but a subset of it, checking source for ConcurrentLinkedDeque will give you more clarity on this.

2: From javadoc of ConcurrentLinkedDeque:

Beware that, unlike in most collections, the size method is NOT a constant-time operation.

..

Additionally, the bulk operations addAll, removeAll, retainAll, containsAll, equals, and toArray are not guaranteed to be performed atomically.

Above is not true for LinkedBlockingDeque