  This paper proposes a new concurrent heap algorithm, based on a stateless
shape property, which efficiently maintains balance during insert and removeMin
operations implemented with hand-over-hand locking. It also provides a O(1)
linearizable snapshot operation based on lazy copy-on-write semantics. Such
snapshots can be used to provide consistent views of the heap during iteration,
as well as to make speculative updates (which can later be dropped).
  The simplicity of the algorithm allows it to be easily proven correct, and
the choice of shape property provides priority queue performance which is
competitive with highly optimized skiplist implementations (and has stronger
bounds on worst-case time complexity).
  A Scala reference implementation is provided.
