Make globals use sharedCAF

The use of globals is quite painful when multiple rts are loaded, e.g.
when plugins are loaded, which bring in a second rts. The sharedCAF
appraoch was employed for the FastStringTable; I've taken the libery
to extend this to the other globals I could find.

Reviewers: rwbarton, simonmar, austin, hvr, erikd, bgamari

Reviewed By: simonmar, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2575

1 files changed, 34 insertions, 0 deletions

diff --git a/compiler/utils/Util.hs b/compiler/utils/Util.hs
index 3104c747a1..88b5090f0a 100644
--- a/compiler/utils/Util.hs
+++ b/compiler/utils/Util.hs
@@ -104,6 +104,7 @@ module Util (
         hSetTranslit,
 
         global, consIORef, globalM,
+        sharedGlobal, sharedGlobalM,
 
         -- * Filenames and paths
         Suffix,
@@ -144,6 +145,7 @@ import qualified GHC.Stack
 import Control.Applicative ( liftA2 )
 import Control.Monad    ( liftM )
 import GHC.IO.Encoding (mkTextEncoding, textEncodingName)
+import GHC.Conc.Sync ( sharedCAF )
 import System.IO (Handle, hGetEncoding, hSetEncoding)
 import System.IO.Error as IO ( isDoesNotExistError )
 import System.Directory ( doesDirectoryExist, getModificationTime )
@@ -930,6 +932,28 @@ seqList :: [a] -> b -> b
 seqList [] b = b
 seqList (x:xs) b = x `seq` seqList xs b
 
+
+{-
+************************************************************************
+*                                                                      *
+                        Globals and the RTS
+*                                                                      *
+************************************************************************
+
+When a plugin is loaded, it currently gets linked against a *newly
+loaded* copy of the GHC package. This would not be a problem, except
+that the new copy has its own mutable state that is not shared with
+that state that has already been initialized by the original GHC
+package.
+
+(Note that if the GHC executable was dynamically linked this
+wouldn't be a problem, because we could share the GHC library it
+links to; this is only a problem if DYNAMIC_GHC_PROGRAMS=NO.)
+
+The solution is to make use of @sharedCAF@ through @sharedGlobal@
+for globals that are shared between multiple copies of ghc packages.
+-}
+
 -- Global variables:
 
 global :: a -> IORef a
@@ -942,6 +966,16 @@ consIORef var x = do
 globalM :: IO a -> IORef a
 globalM ma = unsafePerformIO (ma >>= newIORef)
 
+-- Shared global variables:
+
+sharedGlobal :: a -> (Ptr (IORef a) -> IO (Ptr (IORef a))) -> IORef a
+sharedGlobal a get_or_set = unsafePerformIO $
+  newIORef a >>= flip sharedCAF get_or_set
+
+sharedGlobalM :: IO a -> (Ptr (IORef a) -> IO (Ptr (IORef a))) -> IORef a
+sharedGlobalM ma get_or_set = unsafePerformIO $
+  ma >>= newIORef >>= flip sharedCAF get_or_set
+
 -- Module names:
 
 looksLikeModuleName :: String -> Bool