Documented InterruptibleDelay.

1 files changed, 18 insertions, 10 deletions

diff --git a/InterruptibleDelay.hs b/InterruptibleDelay.hs
index d59ec8ef..b2683441 100644
--- a/InterruptibleDelay.hs
+++ b/InterruptibleDelay.hs
@@ -2,8 +2,9 @@ module InterruptibleDelay where
 
 import Control.Concurrent
 import Control.Monad
-import Control.Exception ({-evaluate,-}handle,ErrorCall(..))
+import Control.Exception ({-evaluate,-}handle,finally,throwIO)
 import Data.Time.Clock (NominalDiffTime)
+import System.IO.Error
 
 type Microseconds = Int
 
@@ -18,24 +19,31 @@ interruptibleDelay :: IO InterruptibleDelay
 interruptibleDelay = do
     fmap InterruptibleDelay newEmptyMVar
 
+-- | Delay for the given number of microseconds and return 'True' if the delay
+-- is not interrupted.
+--
+-- Note: If a thread is already waiting on the given 'InterruptibleDelay'
+-- object, then this will block until it becomes available and only then start
+-- the delay timer.
 startDelay :: InterruptibleDelay -> Microseconds -> IO Bool
 startDelay d interval = do
     thread <- myThreadId
-    handle (\(ErrorCall _)-> do
-                debugNoise $ "delay interrupted"
-                return False) $ do 
+    handle (\e -> do when (not $ isUserError e) (throwIO e)
+                     return False) $ do
         putMVar (delayThread d) thread
         threadDelay interval
         void $ takeMVar (delayThread d)
         return True
+     -- The following cleanup shouldn't be necessary, but I'm paranoid.
+     `finally` tryTakeMVar (delayThread d)
 
   where debugNoise str = return ()
 
-
+-- | Signal the thread waiting on the given 'InterruptibleDelay' object to
+-- continue even though the timeout has not elapsed. If no thread is waiting,
+-- then this is a no-op.
 interruptDelay :: InterruptibleDelay -> IO ()
 interruptDelay d = do
-    mthread <- do
-        tryTakeMVar (delayThread d)
-    flip (maybe $ return ()) mthread $ \thread -> do
-    throwTo thread (ErrorCall "Interrupted delay")
-
+    mthread <- tryTakeMVar (delayThread d)
+    forM_ mthread $ \thread -> do
+    throwTo thread (userError "Interrupted delay")