A Deque is a double-ended queue with a
pop method that can block until
an element is available. It is commonly used to synchronize threads.
Create a new Deque instance which is initially empty.
Tries to retrieve an element from the front of
If an element is available, it is removed from the queue and returned.
If no element is available and
null is returned.
Otherwise, execution blocks until an element is available and returns it.