Message8604

We need to revisit the implementation of deque. Per https://docs.python.org/2/library/collections.html#collections.deque, operations are threadsafe. We do not currently implement this threadsafety requirement in Jython's implementation.

For the unbounded case, we should use http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ConcurrentLinkedDeque.html, which is new with Java 7. This seems to be a more or less exact match.

For the bounded case (with maxlen), the discard semantics are interesting and certainly not those of a synchronized ArrayDeque. We probably want to use an array of PyObject of size maxlen; then implement synchronized methods.

Exposing both approaches with the same API will require a modest amount of cleverness.