Make the dynamic linker thread-safe.

  
The current implementation is rather pessimistic.  The persistent
linker state is now an MVar and all exported Linker functions are
wrapped in modifyMVar calls.  This is serves as a big lock around all
linker functions.

There might be a chance for more concurrency in a few places. E.g.,
extending the closure environment and loading packages might be
independent in some cases.  But for now it's better to be on the safe
side.

1 files changed, 10 insertions, 1 deletions

diff --git a/compiler/utils/Util.lhs b/compiler/utils/Util.lhs
index 3de52b6737..5cf020f7f5 100644
--- a/compiler/utils/Util.lhs
+++ b/compiler/utils/Util.lhs
@@ -65,7 +65,7 @@ module Util (
         doesDirNameExist,
         modificationTimeIfExists,
 
-        global, consIORef,
+        global, consIORef, globalMVar, globalEmptyMVar,
 
         -- * Filenames and paths
         Suffix,
@@ -83,6 +83,7 @@ import Data.IORef       ( IORef, newIORef )
 import System.IO.Unsafe ( unsafePerformIO )
 import Data.IORef       ( readIORef, writeIORef )
 import Data.List        hiding (group)
+import Control.Concurrent.MVar ( MVar, newMVar, newEmptyMVar )
 
 #ifdef DEBUG
 import qualified Data.List as List ( elem, notElem )
@@ -699,6 +700,14 @@ consIORef var x = do
   writeIORef var (x:xs)
 \end{code}
 
+\begin{code}
+globalMVar :: a -> MVar a
+globalMVar a = unsafePerformIO (newMVar a)
+
+globalEmptyMVar :: MVar a
+globalEmptyMVar = unsafePerformIO newEmptyMVar
+\end{code}
+
 Module names:
 
 \begin{code}