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54 lines
1.4 KiB
Haskell
54 lines
1.4 KiB
Haskell
-- |
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-- Module : Control.Concurrent.Classy.QSem
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-- Copyright : (c) 2016 Michael Walker
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-- License : MIT
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-- Maintainer : Michael Walker <mike@barrucadu.co.uk>
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-- Stability : stable
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-- Portability : portable
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--
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-- Simple quantity semaphores.
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module Control.Concurrent.Classy.QSem
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( -- * Simple Quantity Semaphores
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QSem
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, newQSem
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, waitQSem
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, signalQSem
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) where
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import Control.Concurrent.Classy.QSemN
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import Control.Monad.Conc.Class (MonadConc)
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-- | @QSem@ is a quantity semaphore in which the resource is acquired
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-- and released in units of one. It provides guaranteed FIFO ordering
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-- for satisfying blocked 'waitQSem' calls.
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--
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-- The pattern
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--
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-- > bracket_ qaitQSem signalSSem (...)
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--
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-- is safe; it never loses a unit of the resource.
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--
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-- @since 1.0.0.0
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newtype QSem m = QSem (QSemN m)
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-- | Build a new 'QSem' with a supplied initial quantity. The initial
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-- quantity must be at least 0.
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--
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-- @since 1.0.0.0
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newQSem :: MonadConc m => Int -> m (QSem m)
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newQSem initial
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| initial < 0 = fail "newQSem: Initial quantity mus tbe non-negative."
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| otherwise = QSem <$> newQSemN initial
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-- | Wait for a unit to become available.
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--
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-- @since 1.0.0.0
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waitQSem :: MonadConc m => QSem m -> m ()
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waitQSem (QSem qSemN) = waitQSemN qSemN 1
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-- | Signal that a unit of the 'QSem' is available.
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--
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-- @since 1.0.0.0
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signalQSem :: MonadConc m => QSem m -> m ()
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signalQSem (QSem qSemN) = signalQSemN qSemN 1
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