diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,30 @@
+Copyright (c) 2014, David Turner
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of David Turner nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/Setup.hs b/Setup.hs
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--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/alarmclock.cabal b/alarmclock.cabal
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--- /dev/null
+++ b/alarmclock.cabal
@@ -0,0 +1,35 @@
+name:                alarmclock
+version:             0.1.0.0
+synopsis:            Wake up and perform an action at a certain time.
+description:         Wake up and perform an action at a certain time.
+homepage:            https://bitbucket.org/davecturner/alarmclock
+license:             BSD3
+license-file:        LICENSE
+author:              David Turner
+maintainer:          dave.c.turner@gmail.com
+copyright:           (c) David Turner 2014
+category:            Concurrency
+build-type:          Simple
+cabal-version:       >=1.10
+
+library
+  exposed-modules:     Control.Concurrency.AlarmClock
+  build-depends:
+      base >=4.7 && <4.8
+    , time
+    , timeout
+  hs-source-dirs:      src
+  default-language:    Haskell2010
+  ghc-options: -Wall
+
+test-suite test
+  type: exitcode-stdio-1.0
+  main-is: Main.hs
+  hs-source-dirs: test
+  default-language:   Haskell2010
+  build-depends:      base
+                    , alarmclock
+                    , HUnit
+                    , test-framework
+                    , test-framework-hunit
+                    , time
diff --git a/src/Control/Concurrency/AlarmClock.hs b/src/Control/Concurrency/AlarmClock.hs
new file mode 100644
--- /dev/null
+++ b/src/Control/Concurrency/AlarmClock.hs
@@ -0,0 +1,64 @@
+{-# LANGUAGE LambdaCase #-}
+
+{-| Device for running an action at (i.e. shortly after) a certain time, which
+    can be used to implement things like time-based cache expiry.
+
+    This implementation avoids the use of polling to achieve low-latency without
+    lots of computational overhead.
+
+    The alarm can be set multiple times, and in this case the alarm action
+    will run on the earliest such time. If the alarm is set in the past,
+    the action will run immediately. When the action runs, it clears all
+    future alarms; the action can itself return the time at which it should
+    run again.
+
+-}
+
+module Control.Concurrency.AlarmClock where
+
+import Control.Concurrent
+import Control.Exception
+import Control.Monad
+import System.Timeout
+import Data.Time
+
+{-| An 'AlarmClock' is a device for running an action at (or shortly after) a certain time. -}
+data AlarmClock = AlarmClock (MVar UTCTime) ThreadId
+
+mkAlarmClock :: IO (Maybe UTCTime) -> IO AlarmClock
+mkAlarmClock onWakeUp = do
+  mv <- newEmptyMVar
+  tid <- mask $ \restore -> forkIO $ runAlarmClock mv $ void $ forkIO $
+    restore onWakeUp >>= \case Nothing -> return ()
+                               Just wakeUpTime -> setAlarmVar mv wakeUpTime 
+  return $ AlarmClock mv tid
+
+destroyAlarmClock :: AlarmClock -> IO ()
+destroyAlarmClock (AlarmClock _ tid) = killThread tid
+
+setAlarmVar :: MVar UTCTime -> UTCTime -> IO ()
+setAlarmVar mv wakeUpTime = tryTakeMVar mv >>= \case
+  Nothing          -> putMVar mv      wakeUpTime
+  Just wakeUpTime' -> putMVar mv (min wakeUpTime wakeUpTime')
+
+setAlarm :: AlarmClock -> UTCTime -> IO ()
+setAlarm (AlarmClock mv _) = setAlarmVar mv
+
+runAlarmClock :: MVar UTCTime -> IO () -> IO ()
+runAlarmClock wakeUpTimeVar wakeUpAction = alarmNotSet
+  where
+  alarmNotSet = takeMVar wakeUpTimeVar >>= alarmSet
+
+  alarmSet wakeUpTime = do
+    t <- getCurrentTime
+    let dt = diffUTCTime wakeUpTime t
+    if dt < 0 then wakeUpAction >> alarmNotSet
+              else do
+      let dt_usec = ceiling (1000000 * dt) :: Integer
+      let dt_usec_int = if dt_usec > fromIntegral (maxBound :: Int) then maxBound else fromIntegral dt_usec
+      timeout dt_usec_int (takeMVar wakeUpTimeVar) >>= \case
+        Nothing -> do
+          t' <- getCurrentTime
+          if t' < wakeUpTime then alarmSet wakeUpTime else wakeUpAction >> alarmNotSet
+        Just wakeUpTime' -> alarmSet (min wakeUpTime wakeUpTime')
+
diff --git a/test/Main.hs b/test/Main.hs
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--- /dev/null
+++ b/test/Main.hs
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+module Main (main) where
+
+main :: IO ()
+main = return ()