Extending GHC to support building modules in parallel

by Patrick Palka for haskell.org

The aim of this project is to implement native support for building modules in parallel in GHC. This entails making the compilation pipeline thread-safe, and writing a parallel compilation driver next to the existing sequential driver. Focus will be placed on correctness and deterministic output, with speed a latent concern. Nothing in the user's end should change other than there being a new "-j" flag that specifies the number of modules to build in parallel. The cabal-install project should be augmented with the ability to use this new -j flag to speed up builds, alongside its existing package-level parallelization.