An aspect of the present invention reduces blocking instances in parallel processing systems performing operations on trees. In one embodiment, a change operation is performed in a first execution entity and a traversal operation is performed in a second execution entity, with both the change operation and the traversal operation being designed to operate on a same node of a tree, and with the first execution entity and the second execution entity being executed concurrently in a digital processing system. A non-blocking access of the same node to both of the first execution entity and the second execution entity is permitted, thereby enabling the change operation and the traversal operation to be performed concurrently.