From cb28281a2acabf87e91582ce5ace562544ae2730 Mon Sep 17 00:00:00 2001
From: Joe Crayne <joe@jerkface.net>
Date: Mon, 13 Jan 2020 06:58:48 -0500
Subject: Fixed race condition in thread instrumentation.

---
 .../src/Control/Concurrent/Lifted/Instrument.hs    | 75 +++++++++++-----------
 1 file changed, 37 insertions(+), 38 deletions(-)

diff --git a/lifted-concurrent/src/Control/Concurrent/Lifted/Instrument.hs b/lifted-concurrent/src/Control/Concurrent/Lifted/Instrument.hs
index a0bb7dc5..bd6ee4b8 100644
--- a/lifted-concurrent/src/Control/Concurrent/Lifted/Instrument.hs
+++ b/lifted-concurrent/src/Control/Concurrent/Lifted/Instrument.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE RankNTypes #-}
 module Control.Concurrent.Lifted.Instrument
     ( module Control.Concurrent.Lifted
     , forkLabeled
@@ -11,6 +12,7 @@ module Control.Concurrent.Lifted.Instrument
     , PerThread(..)
     ) where
 
+import Control.Concurrent as Raw (forkOSWithUnmask)
 import qualified Control.Concurrent.Lifted as Raw
 import Control.Concurrent.Lifted hiding (fork,forkOS)
 import Control.Exception (fromException)
@@ -47,28 +49,29 @@ globals = unsafePerformIO $ newMVar $ GlobalState
 
 forkLabeled :: HasCallStack => String -> IO () -> IO ThreadId
 forkLabeled lbl action = do
-    t <- instrumented GHC.forkIO action
+    t <- instrumented GHC.forkIOWithUnmask action
     labelThread t lbl
     return t
 {-# INLINE forkLabeled #-}
 
 forkOSLabeled :: HasCallStack => String -> IO () -> IO ThreadId
 forkOSLabeled lbl action = do
-    t <- instrumented Raw.forkOS action
+    t <- instrumented Raw.forkOSWithUnmask action
     labelThread t lbl
     return t
 {-# INLINE forkOSLabeled #-}
 
 forkIO :: HasCallStack => IO () -> IO ThreadId
-forkIO = instrumented GHC.forkIO
+forkIO = instrumented GHC.forkIOWithUnmask
 {-# INLINE forkIO #-}
 
-forkOS :: ( HasCallStack, MonadBaseControl IO m ) => m () -> m ThreadId
-forkOS = instrumented Raw.forkOS
+forkOS :: -- ( HasCallStack, MonadBaseControl IO m ) => m () -> m ThreadId
+          HasCallStack => IO () -> IO ThreadId
+forkOS = instrumented Raw.forkOSWithUnmask
 {-# INLINE forkOS #-}
 
 fork :: ( HasCallStack, MonadBaseControl IO m ) => m () -> m ThreadId
-fork = instrumented Raw.fork
+fork = instrumented Raw.forkWithUnmask
 {-# INLINE fork #-}
 
 shortCallStack :: [([Char], SrcLoc)] -> String
@@ -80,47 +83,43 @@ defaultLabel stack = case getCallStack stack of
     _ : sites  -> shortCallStack sites
     sites -> shortCallStack sites
 
+
 instrumented :: ( HasCallStack, MonadBaseControl IO m ) =>
-                (m () -> m ThreadId) -> m () -> m ThreadId
+                (((forall a. m a -> m a) -> m ()) -> m ThreadId) -> m () -> m ThreadId
 instrumented rawFork action = do
     mvar <- newEmptyMVar
-    t <- rawFork $ do
-        tid <- myThreadId
-        tm <- liftBase getCurrentTime
-        bracket_ (modifyThreads $! \ts -> Map.union ts (Map.singleton tid (PerThread (defaultLabel callStack) tm)))
-                 (return ())
-            $ do catch action $ \e -> case fromException e of
-                    Just ThreadKilled -> return ()
+    tm <- liftBase getCurrentTime
+    t <- mask_ $ rawFork $ \unmask -> do
+            tid <- myThreadId
+            let scrapIt = do takeMVar mvar
+                             modifyThreads $! Map.delete tid
+            io <- catch (unmask action >> return scrapIt) $ \e -> case fromException e of
+                    Just ThreadKilled -> return scrapIt
                     Nothing           -> liftBase $ do
-                        bracket (takeMVar globals)
-                                (\g -> do
-                                    let l = concat [ show e
-                                                   , " ("
-                                                   , maybe "" lbl $ Map.lookup tid (threads g)
-                                                   , ")"
-                                                   ]
-                                    foldr seq (return ()) l
-                                    putMVar globals $! g { threads = Map.insert tid (PerThread l tm) $ threads g }
-                                    throwIO e)
-                                (\g -> do
-                                    let l = concat [ show e
-                                                   , " ("
-                                                   , maybe "" lbl $ Map.lookup tid (threads g)
-                                                   , ")"
-                                                   ]
-                                    reportException g l)
-                 -- Remove the thread only if it terminated normally or was killed.
-                 takeMVar mvar
-                 modifyThreads $! Map.delete tid
-    liftBase $ labelThread_ t (defaultLabel callStack)
+                        g <- takeMVar globals
+                        let l = concat [ show e
+                                       , " ("
+                                       , maybe "" lbl $ Map.lookup tid (threads g)
+                                       , ")"
+                                       ]
+                        reportException g l
+                        let l = concat [ show e
+                                       , " ("
+                                       , maybe "" lbl $ Map.lookup tid (threads g)
+                                       , ")"
+                                       ]
+                        foldr seq (return ()) l
+                        putMVar globals $! g { threads = Map.insert tid (PerThread l tm) $ threads g }
+                        return $ return () -- Remove the thread only if it terminated normally or was killed.
+            io -- scrap record on normal termination
+    liftBase $ labelThread_ t (defaultLabel callStack) tm
     putMVar mvar ()
     return t
 
-labelThread_ :: ThreadId -> String -> IO ()
-labelThread_ tid s = do
+labelThread_ :: ThreadId -> String -> UTCTime -> IO ()
+labelThread_ tid s tm = do
     foldr seq (return ()) s
     GHC.labelThread tid s
-    tm <- liftBase getCurrentTime
     let updateIt (Just pt) = Just $ pt { lbl = s }
         updateIt Nothing   = Just $ PerThread s tm
     modifyThreads $! Map.alter updateIt tid
-- 
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