winio: Add IOPort synchronization primitive

3 files changed, 107 insertions, 0 deletions

diff --git a/libraries/base/GHC/Conc/Sync.hs b/libraries/base/GHC/Conc/Sync.hs
index d6ffbc2de9..80287c56c4 100644
--- a/libraries/base/GHC/Conc/Sync.hs
+++ b/libraries/base/GHC/Conc/Sync.hs
@@ -538,6 +538,8 @@ data BlockReason
         -- ^blocked in 'retry' in an STM transaction
   | BlockedOnForeignCall
         -- ^currently in a foreign call
+  | BlockedOnIOCompletion
+        -- ^currently blocked on an I/O Completion port
   | BlockedOnOther
         -- ^blocked on some other resource.  Without @-threaded@,
         -- I\/O and 'Control.Concurrent.threadDelay' show up as
@@ -576,6 +578,7 @@ threadStatus (ThreadId t) = IO $ \s ->
      mk_stat 11 = ThreadBlocked BlockedOnForeignCall
      mk_stat 12 = ThreadBlocked BlockedOnException
      mk_stat 14 = ThreadBlocked BlockedOnMVar -- possibly: BlockedOnMVarRead
+     mk_stat 15 = ThreadBlocked BlockedOnIOCompletion
      -- NB. these are hardcoded in rts/PrimOps.cmm
      mk_stat 16 = ThreadFinished
      mk_stat 17 = ThreadDied
diff --git a/libraries/base/GHC/IOPort.hs b/libraries/base/GHC/IOPort.hs
new file mode 100644
index 0000000000..e4890d0989
--- /dev/null
+++ b/libraries/base/GHC/IOPort.hs
@@ -0,0 +1,100 @@
+{-# LANGUAGE Unsafe #-}
+{-# LANGUAGE NoImplicitPrelude, MagicHash, UnboxedTuples #-}
+{-# OPTIONS_GHC -funbox-strict-fields #-}
+{-# OPTIONS_HADDOCK hide #-}
+
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  GHC.IOPort
+-- Copyright   :  (c) Tamar Christina 2019
+-- License     :  see libraries/base/LICENSE
+--
+-- Maintainer  :  cvs-ghc@haskell.org
+-- Stability   :  internal
+-- Portability :  non-portable (GHC Extensions)
+--
+-- The IOPort type. This is a synchronization primitive similar to IOVar but
+-- without any of the deadlock guarantees that IOVar provides.  The ports are
+-- single write/multiple wait.  Writing to an already full Port will not queue
+-- the value but instead will discard it.
+--
+--
+-----------------------------------------------------------------------------
+
+module GHC.IOPort (
+        -- * IOPorts
+          IOPort(..)
+        , newIOPort
+        , newEmptyIOPort
+        , readIOPort
+        , writeIOPort
+    ) where
+
+import GHC.Base
+
+data IOPort a = IOPort (IOPort# RealWorld a)
+{- ^
+An 'IOPort' is a synchronising variable, used
+for communication between concurrent threads, where it one of the threads is
+controlled by an external state. e.g. by an I/O action that is serviced by the
+runtime.  It can be thought of as a box, which may be empty or full.
+
+It is mostly similar to the behavior of MVar except writeIOPort doesn't block if
+the variable is full and the GC won't forcibly release the lock if it thinks
+there's a deadlock.
+-}
+
+-- | @since 4.1.0.0
+instance Eq (IOPort a) where
+        (IOPort ioport1#) == (IOPort ioport2#) =
+            isTrue# (sameIOPort# ioport1# ioport2#)
+
+{-
+M-Vars are rendezvous points for concurrent threads.  They begin
+empty, and any attempt to read an empty M-Var blocks.  When an M-Var
+is written, a single blocked thread may be freed.  Reading an M-Var
+toggles its state from full back to empty.  Therefore, any value
+written to an M-Var may only be read once.  Multiple reads and writes
+are allowed, but there must be at least one read between any two
+writes.
+-}
+
+-- |Create an 'IOPort' which is initially empty.
+newEmptyIOPort  :: IO (IOPort a)
+newEmptyIOPort = IO $ \ s# ->
+    case newIOPort# s# of
+         (# s2#, svar# #) -> (# s2#, IOPort svar# #)
+
+-- |Create an 'IOPort' which contains the supplied value.
+newIOPort :: a -> IO (IOPort a)
+newIOPort value =
+    newEmptyIOPort        >>= \ ioport ->
+    writeIOPort ioport value  >>
+    return ioport
+
+-- |Atomically read the the contents of the 'IOPort'.  If the 'IOPort' is
+-- currently empty, 'readIOPort' will wait until it is full.  After a
+-- 'readIOPort', the 'IOPort' is left empty.
+-- TODO: Figure out how to make this an exception for better debugging.
+--
+-- There is one important property of 'readIOPort':
+--
+--   * Only a single threads can be blocked on an 'IOPort', The second thread
+--     attempting to block will be silently ignored.
+--
+readIOPort :: IOPort a -> IO a
+readIOPort (IOPort ioport#) = IO $ \ s# -> readIOPort# ioport# s#
+
+-- |Put a value into an 'IOPort'.  If the 'IOPort' is currently full,
+-- 'writeIOPort' will return False and not block.
+--
+-- There is one important property of 'writeIOPort':
+--
+--   * Only a single thread can be blocked on an 'IOPort'.
+--
+writeIOPort  :: IOPort a -> a -> IO Bool
+writeIOPort (IOPort ioport#) x = IO $ \ s# ->
+    case writeIOPort# ioport# x s# of
+        (# s, 0# #) -> (# s, False #)
+        (# s, _  #) -> (# s, True #)
+
diff --git a/libraries/base/base.cabal b/libraries/base/base.cabal
index aee0c20d29..1d4178a2bf 100644
--- a/libraries/base/base.cabal
+++ b/libraries/base/base.cabal
@@ -308,6 +308,8 @@ Library
         Type.Reflection
         Type.Reflection.Unsafe
         Unsafe.Coerce
+        -- TODO: remove
+        GHC.IOPort
 
     reexported-modules:
           GHC.Num.Integer
@@ -328,6 +330,8 @@ Library
         GHC.IO.Handle.Lock.NoOp
         GHC.IO.Handle.Lock.Windows
         GHC.StaticPtr.Internal
+        GHC.Event.Internal.Types
+        -- GHC.IOPort -- TODO: hide again after debug
         System.Environment.ExecutablePath
         System.CPUTime.Utils