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Build # 3098

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Pull #663

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<a href="https://github.com/composewell/streamly/commit/<a class=hub.com/composewell/streamly/commit/864ccf846f8893b7071a1f5869af988a61f4aa77">864ccf846<a href="https://github.com/composewell/streamly/commit/864ccf846f8893b7071a1f5869af988a61f4aa77">">Merge </a><a class="double-link" href="https://github.com/composewell/streamly/commit/<a class="double-link" href="https://github.com/composewell/streamly/commit/04fd0ebae78dd0a9a70a2b746477e6cc545a286a">04fd0ebae</a>">04fd0ebae</a><a href="https://github.com/composewell/streamly/commit/864ccf846f8893b7071a1f5869af988a61f4aa77"> into c8c161c34">c8c161c34</a>

Pull Request Pull Request #663: Rename Internal.Mutable.Prim.Var to Internal.Data.IORef.Prim.

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/src/Streamly/Internal/Data/IORef/Prim.hs

{-# LANGUAGE UnboxedTuples #-}

#include "inline.hs"

-- |
-- Module      : Streamly.Internal.Data.IORef.Prim
-- Copyright   : (c) 2019 Composewell Technologies
--
-- License     : BSD3
-- Maintainer  : streamly@composewell.com
-- Stability   : experimental
-- Portability : GHC
--
-- A mutable variable in a mutation capable monad (IO) holding a 'Prim'
-- value. This allows fast modification because of unboxed storage.
--
-- = Multithread Consistency Notes
--
-- In general, any value that straddles a machine word cannot be guaranteed to
-- be consistently read from another thread without a lock.  GHC heap objects
-- are always machine word aligned, therefore, a 'IORef' is also word aligned.
-- On a 64-bit platform, writing a 64-bit aligned type from one thread and
-- reading it from another thread should give consistent old or new value. The
-- same holds true for 32-bit values on a 32-bit platform.

module Streamly.Internal.Data.IORef.Prim
    (
      IORef
    , Prim

    -- * Construction
    , newIORef

    -- * Write
    , writeIORef
    , modifyIORef'

    -- * Read
    , readIORef
    )
where

import Control.Monad.Primitive (primitive_)
import Data.Primitive.Types (Prim, sizeOf#, readByteArray#, writeByteArray#)
import GHC.Exts (MutableByteArray#, newByteArray#, RealWorld)
import GHC.IO (IO(..))

-- | An 'IORef' holds a single 'Prim' value.
data IORef a = IORef (MutableByteArray# RealWorld)

-- | Create a new 'IORef'.
--
-- /Internal/
{-# INLINE newIORef #-}
newIORef :: forall a. Prim a => a -> IO (IORef a)
newIORef x = IO (\s# ->
      case newByteArray# (sizeOf# (undefined :: a)) s# of
        (# s1#, arr# #) ->
            case writeByteArray# arr# 0# x s1# of
                s2# -> (# s2#, IORef arr# #)
    )

-- | Write a value to an 'IORef'.
--
-- /Internal/
{-# INLINE writeIORef #-}
writeIORef :: Prim a => IORef a -> a -> IO ()
writeIORef (IORef arr#) x = primitive_ (writeByteArray# arr# 0# x)

-- | Read a value from an 'IORef'.
--
-- /Internal/
{-# INLINE readIORef #-}
readIORef :: Prim a => IORef a -> IO a
readIORef (IORef arr#) = IO (readByteArray# arr# 0#)

-- | Modify the value of an 'IORef' using a function with strict application.
--
-- /Internal/
{-# INLINE modifyIORef' #-}
modifyIORef' :: Prim a => IORef a -> (a -> a) -> IO ()
modifyIORef' (IORef arr#) g = primitive_ $ \s# ->
  case readByteArray# arr# 0# s# of
    (# s'#, a #) -> let a' = g a in a' `seq` writeByteArray# arr# 0# a' s'#

1	{-# LANGUAGE UnboxedTuples #-}
2
3	#include "inline.hs"
4
5	-- \|
6	-- Module : Streamly.Internal.Data.IORef.Prim
7	-- Copyright : (c) 2019 Composewell Technologies
8	--
9	-- License : BSD3
10	-- Maintainer : streamly@composewell.com
11	-- Stability : experimental
12	-- Portability : GHC
13	--
14	-- A mutable variable in a mutation capable monad (IO) holding a 'Prim'
15	-- value. This allows fast modification because of unboxed storage.
16	--
17	-- = Multithread Consistency Notes
18	--
19	-- In general, any value that straddles a machine word cannot be guaranteed to
20	-- be consistently read from another thread without a lock. GHC heap objects
21	-- are always machine word aligned, therefore, a 'IORef' is also word aligned.
22	-- On a 64-bit platform, writing a 64-bit aligned type from one thread and
23	-- reading it from another thread should give consistent old or new value. The
24	-- same holds true for 32-bit values on a 32-bit platform.
25
26	module Streamly.Internal.Data.IORef.Prim
27	(
28	IORef
29	, Prim
30
31	-- * Construction
32	, newIORef
33
34	-- * Write
35	, writeIORef
36	, modifyIORef'
37
38	-- * Read
39	, readIORef
40	)
41	where
42
43	import Control.Monad.Primitive (primitive_)
44	import Data.Primitive.Types (Prim, sizeOf#, readByteArray#, writeByteArray#)
45	import GHC.Exts (MutableByteArray#, newByteArray#, RealWorld)
46	import GHC.IO (IO(..))
47
48	-- \| An 'IORef' holds a single 'Prim' value.
49	data IORef a = IORef (MutableByteArray# RealWorld)
50
51	-- \| Create a new 'IORef'.
52	--
53	-- /Internal/
54	{-# INLINE newIORef #-}
55	newIORef :: forall a. Prim a => a -> IO (IORef a)
56	newIORef x = IO (\s# ->	×
57	case newByteArray# (sizeOf# (undefined :: a)) s# of	×
58	(# s1#, arr# #) ->
59	case writeByteArray# arr# 0# x s1# of	×
60	s2# -> (# s2#, IORef arr# #)	×
61	)
62
63	-- \| Write a value to an 'IORef'.
64	--
65	-- /Internal/
66	{-# INLINE writeIORef #-}
67	writeIORef :: Prim a => IORef a -> a -> IO ()
68	writeIORef (IORef arr#) x = primitive_ (writeByteArray# arr# 0# x)	×
69
70	-- \| Read a value from an 'IORef'.
71	--
72	-- /Internal/
73	{-# INLINE readIORef #-}
74	readIORef :: Prim a => IORef a -> IO a
75	readIORef (IORef arr#) = IO (readByteArray# arr# 0#)	×
76
77	-- \| Modify the value of an 'IORef' using a function with strict application.
78	--
79	-- /Internal/
80	{-# INLINE modifyIORef' #-}
81	modifyIORef' :: Prim a => IORef a -> (a -> a) -> IO ()
82	modifyIORef' (IORef arr#) g = primitive_ $ \s# ->	×
83	case readByteArray# arr# 0# s# of	×
84	(# s'#, a #) -> let a' = g a in a' `seq` writeByteArray# arr# 0# a' s'#	×

composewell / streamly / 3098

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