Add a parallel forEach() method in NonBlockingHashMap

[justinhorvitz]

Feature Request

Add a method to NonBlockingHashMap similar to the parallel forEach method in ConcurrentHashMap.

Background

In Bazel we currently use Guava's interners, but we are looking at other strategies for interning in order to reduce storage cost. Our estimate is that > 6% of Bazel's memory cost is from the interning data structures (not including the elements, just the storage).

We are interested in switching from ConcurrentHashMap to NonBlockingHashMap primarily for the getk() method, which would allow Bazel's main graph map to double as an interner for its keys, replacing Guava interners and the storage cost they entail. A parallel iteration method would close the gap vs our current usage of ConcurrentHashMap.

[Bue-von-hon]

@nitsanw i'll give it a try

[justinhorvitz]

Fyi - we no longer need this feature for Bazel, as we found a way to pack the keys into the values.