dejafu/dejafu-tests/lib/Examples/ParMonad/DirectInternal.hs

#line 1 "monad-par/Control/Monad/Par/Scheds/DirectInternal.hs"
{-# LANGUAGE PackageImports, CPP, GeneralizedNewtypeDeriving #-}

{-
The monad-par package:
https://hackage.haskell.org/package/monad-par

This is the code from Control.Monad.Par.Scheds.DirectInternal, with
CPP expanded in its default configuration, modified to use MonadConc.

- - - - -

Copyright Simon Marlow, Ryan Newton 2011

All rights reserved.

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    * Redistributions in binary form must reproduce the above
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      with the distribution.

    * Neither the name of the authors nor the names of other
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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-}

-- | Type definiton and some helpers.  This is used mainly by
-- Direct.hs but can also be used by other modules that want access to
-- the internals of the scheduler (i.e. the private `Par` type constructor).

module Examples.ParMonad.DirectInternal where

import Control.Applicative
import "mtl" Control.Monad.Cont as C
import qualified "mtl" Control.Monad.Reader as RD

import qualified System.Random.MWC as Random

import Control.Concurrent.Classy hiding (yield)
import GHC.Conc
import Data.IORef
import qualified Data.Set as S
import Data.Word (Word64)
import Data.Concurrent.Deque.Class (WSDeque)

import Data.Concurrent.Deque.Reference.DequeInstance
import Data.Concurrent.Deque.Reference as R


-- Our monad stack looks like this:
--      ---------
--        ContT
--       ReaderT
--         IO
--      ---------
-- The ReaderT monad is there for retrieving the scheduler given the
-- fact that the API calls do not get it as an argument.
--
-- Note that the result type for continuations is unit.  Forked
-- computations return nothing.
--
newtype Par m a = Par { unPar :: C.ContT () (ROnly m) a }
    deriving (Functor, Applicative, Monad, MonadCont, RD.MonadReader (Sched m))
type ROnly m = RD.ReaderT (Sched m) m

type SessionID = Word64

-- An ID along with a flag to signal completion:
data Session m = Session SessionID (HotVar m Bool)

data Sched m = Sched
    {
      ---- Per worker ----
      no       :: {-# UNPACK #-} !Int,
      workpool :: WSDeque (Par m ()),
      rng      :: HotVar m Random.GenIO, -- Random number gen for work stealing.
      isMain :: Bool, -- Are we the main/master thread?

      -- The stack of nested sessions that THIS worker is participating in.
      -- When a session finishes, the worker can return to its Haskell
      -- calling context (it's "real" continuation).
      sessions :: HotVar m [Session m],
      -- (1) This is always non-empty, containing at least the root
      --     session corresponding to the anonymous system workers.
      -- (2) The original invocation of runPar also counts as a session
      --     and pushes a second
      -- (3) Nested runPar invocations may push further sessions onto the stack.

      ---- Global data: ----
      idle     :: HotVar m [MVar m Bool], -- waiting idle workers
      scheds   :: [Sched m],            -- A global list of schedulers.

      -- Any thread that enters runPar (original or nested) registers
      -- itself in this global list.  When the list becomes null,
      -- worker threads may shut down or at least go idle.
      activeSessions :: HotVar m (S.Set SessionID),

      -- A counter to support unique session IDs:
      sessionCounter :: HotVar m SessionID
     }


--------------------------------------------------------------------------------
-- Helpers #1:  Atomic Variables
--------------------------------------------------------------------------------
-- TEMP: Experimental

newHotVar      :: MonadConc m => a -> m (HotVar m a)
modifyHotVar   :: MonadConc m => HotVar m a -> (a -> (a,b)) -> m b
modifyHotVar_  :: MonadConc m => HotVar m a -> (a -> a) -> m ()
writeHotVar    :: MonadConc m => HotVar m a -> a -> m ()
readHotVar     :: MonadConc m => HotVar m a -> m a
readHotVarRaw  :: MonadConc m => HotVar m a -> m a
writeHotVarRaw :: MonadConc m => HotVar m a -> a -> m ()

{-# INLINE newHotVar     #-}
{-# INLINE modifyHotVar  #-}
{-# INLINE modifyHotVar_ #-}
{-# INLINE readHotVar    #-}
{-# INLINE writeHotVar   #-}

type HotVar m a = CRef m a
newHotVar     = newCRef
modifyHotVar  = atomicModifyCRef
modifyHotVar_ v fn = atomicModifyCRef v (\a -> (fn a, ()))
readHotVar    = readCRef
writeHotVar   = writeCRef
instance Show (IORef a) where
  show ref = "<ioref>"

-- hotVarTransaction = id
hotVarTransaction = error "Transactions not currently possible for IO refs"
readHotVarRaw  = readHotVar
writeHotVarRaw = writeHotVar