[erlang] perform AST extraction in parallel
[erlang] perform AST extraction in parallel

Summary: Erlang AST extraction performed sequentially can lead to poor performance of big projects.

Reviewed By: rgrig

Differential Revision: D30669829

fbshipit-source-id: eed04d2ba

jvillard/infer,facebook/infer,facebook/infer,facebook/infer,jvillard/infer,jvillard/infer,facebook/infer,jvillard/infer,jvillard/infer,facebook/infer,jvillard/infer,facebook/infer,facebook/infer,jvillard/infer