Split off the concurrent hierarchy (concurrent, unique, timeout)

[ghc-base.git] / Control / Concurrent / SampleVar.hs

diff --git a/Control/Concurrent/SampleVar.hs b/Control/Concurrent/SampleVar.hs
deleted file mode 100644 (file)
index 69c29c2..0000000
--- a/Control/Concurrent/SampleVar.hs
+++ /dev/null
@@ -1,117 +0,0 @@
------------------------------------------------------------------------------
--- |
--- Module      :  Control.Concurrent.SampleVar
--- Copyright   :  (c) The University of Glasgow 2001
--- License     :  BSD-style (see the file libraries/base/LICENSE)
--- 
--- Maintainer  :  libraries@haskell.org
--- Stability   :  experimental
--- Portability :  non-portable (concurrency)
---
--- Sample variables
---
------------------------------------------------------------------------------
-
-module Control.Concurrent.SampleVar
-       (
-         -- * Sample Variables
-         SampleVar,         -- :: type _ =
- 
-         newEmptySampleVar, -- :: IO (SampleVar a)
-         newSampleVar,      -- :: a -> IO (SampleVar a)
-         emptySampleVar,    -- :: SampleVar a -> IO ()
-         readSampleVar,     -- :: SampleVar a -> IO a
-         writeSampleVar,    -- :: SampleVar a -> a -> IO ()
-         isEmptySampleVar,  -- :: SampleVar a -> IO Bool
-
-       ) where
-
-import Prelude
-
-import Control.Concurrent.MVar
-
--- |
--- Sample variables are slightly different from a normal 'MVar':
--- 
---  * Reading an empty 'SampleVar' causes the reader to block.
---    (same as 'takeMVar' on empty 'MVar')
--- 
---  * Reading a filled 'SampleVar' empties it and returns value.
---    (same as 'takeMVar')
--- 
---  * Writing to an empty 'SampleVar' fills it with a value, and
---    potentially, wakes up a blocked reader (same as for 'putMVar' on
---    empty 'MVar').
---
---  * Writing to a filled 'SampleVar' overwrites the current value.
---    (different from 'putMVar' on full 'MVar'.)
-
-type SampleVar a
- = MVar (Int,           -- 1  == full
-                        -- 0  == empty
-                        -- <0 no of readers blocked
-          MVar a)
-
--- |Build a new, empty, 'SampleVar'
-newEmptySampleVar :: IO (SampleVar a)
-newEmptySampleVar = do
-   v <- newEmptyMVar
-   newMVar (0,v)
-
--- |Build a 'SampleVar' with an initial value.
-newSampleVar :: a -> IO (SampleVar a)
-newSampleVar a = do
-   v <- newEmptyMVar
-   putMVar v a
-   newMVar (1,v)
-
--- |If the SampleVar is full, leave it empty.  Otherwise, do nothing.
-emptySampleVar :: SampleVar a -> IO ()
-emptySampleVar v = do
-   (readers, var) <- takeMVar v
-   if readers > 0 then do
-     takeMVar var
-     putMVar v (0,var)
-    else
-     putMVar v (readers,var)
-
--- |Wait for a value to become available, then take it and return.
-readSampleVar :: SampleVar a -> IO a
-readSampleVar svar = do
---
--- filled => make empty and grab sample
--- not filled => try to grab value, empty when read val.
---
-   (readers,val) <- takeMVar svar
-   putMVar svar (readers-1,val)
-   takeMVar val
-
--- |Write a value into the 'SampleVar', overwriting any previous value that
--- was there.
-writeSampleVar :: SampleVar a -> a -> IO ()
-writeSampleVar svar v = do
---
--- filled => overwrite
--- not filled => fill, write val
---
-   (readers,val) <- takeMVar svar
-   case readers of
-     1 -> 
-       swapMVar val v >> 
-       putMVar svar (1,val)
-     _ -> 
-       putMVar val v >> 
-       putMVar svar (min 1 (readers+1), val)
-
--- | Returns 'True' if the 'SampleVar' is currently empty.
---
--- Note that this function is only useful if you know that no other
--- threads can be modifying the state of the 'SampleVar', because
--- otherwise the state of the 'SampleVar' may have changed by the time
--- you see the result of 'isEmptySampleVar'.
---
-isEmptySampleVar :: SampleVar a -> IO Bool
-isEmptySampleVar svar = do
-   (readers, _) <- readMVar svar
-   return (readers == 0)
-