Parallel.gr

------
--- Module: Parallel
--- Description: Combinators for parallel programming in Granule
--- Authors: Michael Vollmer, Dominic Orchard
--- License: BSD3
--- Copyright: (c) Authors 2022
--- Issue-tracking: https://github.com/dorchard/granule/issues
--- Repository: https://github.com/dorchard/granule
------

module Parallel where

import List

--- basic parallel combinator (defined in terms of linear channels)
--- `par` expects two thunks, `f` and `g`, and returns their resulting values in a pair
par : forall {a : Type, b : Type} . (() -> a) -> (() -> b) -> (a, b)
par f g =  let c = forkLinear (\c' -> close (send c' (f ()))); -- compute f in new thread
               b = g (); -- compute g in current thread
               (a, c') = recv c; -- get result of f from other thread
               -- (shared memory, should be constant time to share pointer!)
               _ = close c'
           in (a, b)

--- parallel combinator for lists of computations
--- `parList` expects a list of thunks, and returns a list of values (computed in parallel)
parList : forall {a : Type} . List (() -> a) -> List a
parList lst =
  case lst of
    Empty -> Empty;
    (Next f fs) -> case (par f (\x -> case x of
                                   () -> parList fs)) of
                     (e, lst2) -> Next e lst2