i also saw the PR to parallelize resolve and haven't yet reviewed but i was super glad because i'd seen parallelizing resolve induce a wonderful speedup when i was investigating my initial mad dash to make running pex truly instantaneous (which involved fingerprinting "components", aka informally-defined cacheable/parallelizable equivalents to pants targets). https://github.com/pantsbuild/pex/compare/master...cosmicexplorer:incremental-pex-production-with-fingerprinting?expand=1 actually has a much more useful readme at the top than i remember writing! it parallelizes adding source files to the pex in a way that i'm sure has none of the guarantees described in https://github.com/pantsbuild/pex/pull/819.