Fix #4514 - IO manager deadlock

[ghc-base.git] / System / Event / Thread.hs

diff --git a/System/Event/Thread.hs b/System/Event/Thread.hs
index ae3a71a..990bae3 100644 (file)
--- a/System/Event/Thread.hs
+++ b/System/Event/Thread.hs
@@ -5,20 +5,26 @@ module System.Event.Thread
       ensureIOManagerIsRunning
     , threadWaitRead
     , threadWaitWrite
+    , closeFd
     , threadDelay
     , registerDelay
     ) where
 
 import Data.IORef (IORef, newIORef, readIORef, writeIORef)
 import Data.Maybe (Maybe(..))
+import Foreign.C.Error (eBADF, errnoToIOError)
 import Foreign.Ptr (Ptr)
 import GHC.Base
 import GHC.Conc.Sync (TVar, ThreadId, ThreadStatus(..), atomically, forkIO,
                       labelThread, modifyMVar_, newTVar, sharedCAF,
                       threadStatus, writeTVar)
+import GHC.IO.Exception (ioError)
 import GHC.MVar (MVar, newEmptyMVar, newMVar, putMVar, takeMVar)
+import GHC.Real (fromIntegral)
+import System.Event.Internal (eventIs, evtClose)
 import System.Event.Manager (Event, EventManager, evtRead, evtWrite, loop,
                              new, registerFd, unregisterFd_, registerTimeout)
+import qualified System.Event.Manager as M
 import System.IO.Unsafe (unsafePerformIO)
 import System.Posix.Types (Fd)
 
@@ -47,22 +53,43 @@ registerDelay usecs = do
 
 -- | Block the current thread until data is available to read from the
 -- given file descriptor.
+--
+-- This will throw an 'IOError' if the file descriptor was closed
+-- while this thread is blocked.
 threadWaitRead :: Fd -> IO ()
 threadWaitRead = threadWait evtRead
 {-# INLINE threadWaitRead #-}
 
 -- | Block the current thread until the given file descriptor can
 -- accept data to write.
+--
+-- This will throw an 'IOError' if the file descriptor was closed
+-- while this thread is blocked.
 threadWaitWrite :: Fd -> IO ()
 threadWaitWrite = threadWait evtWrite
 {-# INLINE threadWaitWrite #-}
 
+-- | Close a file descriptor in a concurrency-safe way.
+--
+-- Any threads that are blocked on the file descriptor via
+-- 'threadWaitRead' or 'threadWaitWrite' will be unblocked by having
+-- IO exceptions thrown.
+closeFd :: (Fd -> IO ())        -- ^ Action that performs the close.
+        -> Fd                   -- ^ File descriptor to close.
+        -> IO ()
+closeFd close fd = do
+  Just mgr <- readIORef eventManager
+  M.closeFd mgr close fd
+
 threadWait :: Event -> Fd -> IO ()
 threadWait evt fd = do
   m <- newEmptyMVar
   Just mgr <- readIORef eventManager
-  _ <- registerFd mgr (\reg _ -> unregisterFd_ mgr reg >> putMVar m ()) fd evt
-  takeMVar m
+  _ <- registerFd mgr (\reg e -> unregisterFd_ mgr reg >> putMVar m e) fd evt
+  evt' <- takeMVar m
+  if evt' `eventIs` evtClose
+    then ioError $ errnoToIOError "threadWait" eBADF Nothing Nothing
+    else return ()
 
 foreign import ccall unsafe "getOrSetSystemEventThreadEventManagerStore"
     getOrSetSystemEventThreadEventManagerStore :: Ptr a -> IO (Ptr a)