-initInterpBuffering :: GHC.Session -> IO ()
-initInterpBuffering session
- = do -- we don't want to be fooled by any modules lying around in the current
- -- directory when we compile these code fragments, so set the import
- -- path to be empty while we compile them.
- dflags <- GHC.getSessionDynFlags session
- GHC.setSessionDynFlags session dflags{importPaths=[]}
-
- maybe_hval <- GHC.compileExpr session no_buf_cmd
-
- case maybe_hval of
- Just hval -> writeIORef turn_off_buffering (unsafeCoerce# hval :: IO ())
- other -> panic "interactiveUI:setBuffering"
-
- maybe_hval <- GHC.compileExpr session flush_cmd
- case maybe_hval of
- Just hval -> writeIORef flush_interp (unsafeCoerce# hval :: IO ())
- _ -> panic "interactiveUI:flush"
-
- GHC.setSessionDynFlags session dflags
- GHC.workingDirectoryChanged session
+-- After various attempts, I believe this is the least bad way to do
+-- what we want. We know look up the address of the static stdin,
+-- stdout, and stderr closures in the loaded base package, and each
+-- time we need to refer to them we cast the pointer to a Handle.
+-- This avoids any problems with the CAF having been reverted, because
+-- we'll always get the current value.
+--
+-- The previous attempt that didn't work was to compile an expression
+-- like "hSetBuffering stdout NoBuffering" into an expression of type
+-- IO () and run this expression each time we needed it, but the
+-- problem is that evaluating the expression might cache the contents
+-- of the Handle rather than referring to it from its static address
+-- each time. There's no safe workaround for this.
+
+initInterpBuffering :: Ghc ()
+initInterpBuffering = do -- make sure these are linked
+ dflags <- GHC.getSessionDynFlags
+ liftIO $ do
+ initDynLinker dflags
+
+ -- ToDo: we should really look up these names properly, but
+ -- it's a fiddle and not all the bits are exposed via the GHC
+ -- interface.
+ mb_stdin_ptr <- ObjLink.lookupSymbol "base_GHCziHandle_stdin_closure"
+ mb_stdout_ptr <- ObjLink.lookupSymbol "base_GHCziHandle_stdout_closure"
+ mb_stderr_ptr <- ObjLink.lookupSymbol "base_GHCziHandle_stderr_closure"
+
+ let f ref (Just ptr) = writeIORef ref ptr
+ f _ Nothing = panic "interactiveUI:setBuffering2"
+ zipWithM f [stdin_ptr,stdout_ptr,stderr_ptr]
+ [mb_stdin_ptr,mb_stdout_ptr,mb_stderr_ptr]