Added skeleton code for ProcessPool provide by Paul (here:

unisonweb#24) with some minor changes to
make it compile.

node/src/Unison/Runtime/ProcessPool.hs

@@ -0,0 +1,29 @@
+module Unison.Runtime.ProcessPool where
+
+import Data.Bytes.Serial
+import System.Process (ProcessHandle)
+
+newtype TimeBudget = Seconds Int
+newtype SpaceBudget = Megabytes Int
+type Budget = (TimeBudget, SpaceBudget)
+newtype MaxProcesses = MaxProcesses Int
+data Err = TimeExceeded | SpaceExceeded | Killed | InsufficientProcesses
+type ID = Int
+
+data Pool a b = Pool {
+  -- | Evaluate the thunk in a separate process, with the given budget. 
+  -- If there is no available process for that `Budget`, create a new one, 
+  -- unless that would exceed the `MaxProcesses` bound, in which case
+  -- fail fast with `Left InsufficientProcesses`.
+  evaluate :: Budget -> MaxProcesses -> ID -> a -> IO (Either Err b),
+
+  -- | Forcibly kill the process associated with an ID. Any prior `evaluate` for
+  -- that `ID` should complete with `Left Killed`.
+  kill :: ID -> IO (),
+
+  -- | Shutdown the entire pool. After this completes, no other processes should be running
+  shutdown :: IO ()
+}
+
+pool :: (Serial a, Serial b) => IO ProcessHandle -> IO (Pool a b)
+pool createWorker = undefined

node/src/Unison/Runtime/Worker.hs

@@ -0,0 +1,9 @@
+module Unison.Runtime.Worker where
+
+import Data.Bytes.Serial
+
+worker :: (Serial a, Serial b) => (a -> IO b) -> IO ()
+worker eval = undefined
+
+main :: IO ()
+main = undefined

node/unison-node.cabal

@@ -63,6 +63,8 @@ library
     Unison.Runtime.Unfold
     Unison.Runtime.Vector
     Unison.Runtime.ResourcePool
+    Unison.Runtime.ProcessPool
+    Unison.Runtime.Worker
 
   build-depends:
     aeson,
@@ -86,6 +88,7 @@ library
     network,
     network-simple,
     prelude-extras,
+    process,
     scotty,
     sockaddr,
     stm,