45 lines
1.2 KiB
Haskell
45 lines
1.2 KiB
Haskell
{-# LANGUAGE BangPatterns #-}
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-- | This module defines a type for mutable, integer-valued counters.
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-- All operations on counters are thread-safe.
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module System.Remote.Counter
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(
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Counter
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, inc
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, dec
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, add
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, subtract
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, set
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) where
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import Data.IORef (atomicModifyIORef)
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import Prelude hiding (subtract)
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import System.Remote.Counter.Internal
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-- | Increase the counter by one.
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inc :: Counter -> IO ()
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inc (C ref) = do
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!_ <- atomicModifyIORef ref $ \ n -> let n' = n + 1 in (n', n')
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return ()
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-- | Decrease the counter by one.
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dec :: Counter -> IO ()
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dec (C ref) = do
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!_ <- atomicModifyIORef ref $ \ n -> let n' = n - 1 in (n', n')
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return ()
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-- | Increase the counter by the given amount.
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add :: Counter -> Int -> IO ()
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add (C ref) i = do
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!_ <- atomicModifyIORef ref $ \ n -> let n' = n + i in (n', n')
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return ()
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-- | Decrease the counter by the given amount.
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subtract :: Counter -> Int -> IO ()
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subtract (C ref) i = do
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!_ <- atomicModifyIORef ref $ \ n -> let n' = n - i in (n', n')
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return ()
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-- | Set the counter to the given value.
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set :: Counter -> Int -> IO ()
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set (C ref) !i = atomicModifyIORef ref $ \ _ -> (i, ())
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