bounded-qsem (empty) → 0.1.0.0

raw patch · 5 files changed

+122/−0 lines, 5 filesdep +base

Dependencies added: base

Files

• bounded-qsem.cabal +21/−0
• changelog.md +2/−0
• license +21/−0
• readme.md +4/−0
• src/Control/Concurrent/BQSem.hs +74/−0

@@ -0,0 +1,21 @@+name: bounded-qsem+category: Concurrency+synopsis: Bounded quantity semaphores.+description: Bounded quantity semaphores, meaning quantity semaphores that have an+             upper-bound in the number of units that can be available.+version: 0.1.0.0+cabal-version: 1.18+build-type: Simple+author: Daniel Casanueva (daniel.casanueva `at` proton.me)+maintainer: Daniel Casanueva (daniel.casanueva `at` proton.me)+bug-reports: https://gitlab.com/daniel-casanueva/haskell/bounded-qsem/-/issues+license: MIT+license-file: license+extra-doc-files: readme.md, changelog.md++library+  default-language: Haskell2010+  hs-source-dirs: src+  exposed-modules: Control.Concurrent.BQSem+  ghc-options: -Wall+  build-depends: base >= 4.8 && < 4.19

@@ -0,0 +1,2 @@+## 0.1.0.0+* First release.

@@ -0,0 +1,21 @@+MIT License++Copyright (c) 2023 Daniel Casanueva++Permission is hereby granted, free of charge, to any person obtaining a copy+of this software and associated documentation files (the "Software"), to deal+in the Software without restriction, including without limitation the rights+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell+copies of the Software, and to permit persons to whom the Software is+furnished to do so, subject to the following conditions:++The above copyright notice and this permission notice shall be included in all+copies or substantial portions of the Software.++THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE+SOFTWARE.

@@ -0,0 +1,4 @@+# bounded-qsem++Bounded version of the quantity semaphores provided by+[base](https://hackage.haskell.org/package/base/docs/Control-Concurrent-QSem.html).

@@ -0,0 +1,74 @@++{-# LANGUAGE Safe #-}++-- | Bounded quantity semaphores.+module Control.Concurrent.BQSem+  ( BQSem+  , newBQSem+  , waitBQSem+  , signalBQSem+  , getBQSemQuantity+    ) where++import Control.Concurrent.QSem+import Control.Concurrent.MVar+import Control.Exception (mask, onException)+import Control.Monad (unless)++-- | Bounded quantity semaphore in which the resource is acquired and released in units of one,+--   but with a maximum amount of units available at any given time.+data BQSem = BQSem+  { -- | Underlying unbounded quantity semaphore.+    unboundedQSem :: QSem+    -- | Maximum number of units.+  , bqsemBound :: Int+    -- | Counter of current units.+  , bqsemCounter :: MVar Int+    }++-- | Build a new 'BQSem' with supplied initial and maximum supply.+--   An exception is thrown in any of the following cases:+--+--   * Initial supply is negative.+--   * Maximum supply is less than 1.+--   * Initial supply exceeds maximum.+--+newBQSem+  :: Int -- ^ Initial unit supply.+  -> Int -- ^ Maximum unit supply.+  -> IO BQSem+newBQSem n0 m = do+  unless (n0 <= m) $ fail "newBQSem: Initial quantity must be less or equal than maximum."+  unless (m > 0) $ fail "newBQSem: Maximum quantity must be at least 1."+  qsem <- newQSem n0+  counter <- newMVar n0+  pure $ BQSem+    { unboundedQSem = qsem+    , bqsemBound = m+    , bqsemCounter = counter+      }++-- | Wait for a unit to become available.+waitBQSem :: BQSem -> IO ()+waitBQSem bqsem =+  mask $ \restore -> do+    restore $ waitQSem $ unboundedQSem bqsem+    let counter = bqsemCounter bqsem+    takeMVar counter >>=+      \n -> putMVar counter $! n - 1++-- | Make a new unit available, unless the maximum number of units has been reached,+--   in which case it does nothing (it doesn't block).+signalBQSem :: BQSem -> IO ()+signalBQSem bqsem =+  mask $ \restore -> do+    let counter = bqsemCounter bqsem+    n <- takeMVar counter+    if n == bqsemBound bqsem+       then putMVar counter n+       else do restore (signalQSem $ unboundedQSem bqsem) `onException` putMVar counter n+               putMVar counter $! n + 1++-- | Get current supply quantity.+getBQSemQuantity :: BQSem -> IO Int+getBQSemQuantity = readMVar . bqsemCounter