From 452086345c51d77d4aa020400448a1db5297778c Mon Sep 17 00:00:00 2001
From: Harald Steinlechner <haraldsteinlechner@gmail.com>
Date: Mon, 27 Aug 2012 14:28:37 +0200
Subject: [PATCH] scratch/GC: sketched datastructures etc for obj graph
 traversal

---
 scratch/GC.hs | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)
 create mode 100644 scratch/GC.hs

diff --git a/scratch/GC.hs b/scratch/GC.hs
new file mode 100644
index 0000000..d2bece2
--- /dev/null
+++ b/scratch/GC.hs
@@ -0,0 +1,64 @@
+{-# LANGUAGE ScopedTypeVariables #-}
+module GC 
+  ({- dont export generic versions for high performance ;-) -}) where
+
+import Control.Monad
+
+import Data.Foldable hiding (mapM_)
+
+import Foreign.Ptr
+import Foreign.Marshal.Alloc
+import Foreign.Marshal.Array
+import Foreign.Storable
+import GHC.Int
+
+
+class RefObj a where
+  payload :: a -> IO IntPtr
+  refs    :: a -> IO [a]
+  marked  :: a -> IO Bool
+  mark    :: a -> IO ()
+
+
+instance RefObj (Ptr a) where
+  payload     = return . ptrToIntPtr
+  refs        = unpackRefs . castPtr
+  marked      = markedRef
+  mark        = markRef
+
+
+idOff           = 0x0
+numberOfObjsOff = 0x4
+fieldsOff = 0xC
+markedOff = 0x8
+
+unpackRefs :: Ptr Int32 -> IO [Ptr b]
+unpackRefs ptr = do  --dereference number of objs; mark field skipped via fieldsOffset
+                    numberOfObjs <- peekByteOff ptr numberOfObjsOff :: IO Int32
+                    mapM (peekElemOff (ptr `plusPtr` fieldsOff)) [0..fromIntegral $ numberOfObjs-1]
+
+markedRef :: Ptr a -> IO Bool
+markedRef ptr = liftM ((/=0) . fromIntegral) (peekByteOff ptr markedOff :: IO Int32)
+
+markRef :: Ptr a -> IO ()
+markRef ptr = pokeByteOff ptr markedOff (1::Int32)
+
+markTree :: RefObj a => a -> IO ()
+markTree root = marked root >>= (`when` continue) . not
+  where continue = mark root >> refs root >>= mapM_  markTree
+
+
+emptyObj id  = do mem <- mallocBytes 0xC
+                  pokeArray mem [id,0,0::Int32]
+                  return mem
+
+twoRefs = do mem <- mallocBytes 0x14
+             -- idOfObj; numberofObj; marked waste memory Int32
+             pokeArray mem [0::Int32,2,0]
+             obj1 <- emptyObj 1
+             obj2 <- emptyObj 2
+             pokeByteOff mem 0xC obj1
+             pokeByteOff mem (0xC+0x4) obj2
+             return mem
+
+
-- 
2.25.1