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|
{-# LANGUAGE BangPatterns,CPP #-}
module CASList where
import Control.Monad
import Data.IORef
import Control.Concurrent
import Control.Concurrent.Chan
import System.Environment
import Data.Time
-- #define USE_UNPACK
-- #define USE_STRICT
#if defined(USE_UNPACK)
#define UNPACK(p) {-# UNPACK #-} !(p)
#elif defined(USE_STRICT)
#define UNPACK(p) !(p)
#else
#define UNPACK(p) p
#endif
data List a = Node { val :: a
, next :: UNPACK(IORef (List a)) }
| DelNode { next :: UNPACK(IORef (List a)) }
| Null
| Head { next :: UNPACK(IORef (List a)) } deriving Eq
data ListHandle a = ListHandle { headList :: UNPACK(IORef (IORef (List a))),
tailList :: UNPACK(IORef (IORef (List a))) }
{-# INLINE myNext #-}
myNext :: List a -> IORef (List a)
myNext Node{next = n} = n
myNext DelNode{next = n} = n
myNext Head{next = n} = n
myNext _ = error "myNext"
-- we assume a static head pointer, pointing to the first node which must be Head
-- the deleted field of Head is always False, it's only there to make some of the code
-- more uniform
-- tail points to the last node which must be Null
type Iterator a = IORef (IORef (List a))
-------------------------------------------
-- auxilliary functions
while b cmd = if b then do {cmd; while b cmd}
else return ()
repeatUntil cmd = do { b <- cmd; if b then return ()
else repeatUntil cmd }
atomCAS :: Eq a => IORef a -> a -> a -> IO Bool
atomCAS ptr old new =
atomicModifyIORef ptr (\ cur -> if cur == old
then (new, True)
else (cur, False))
atomicWrite :: IORef a -> a -> IO ()
atomicWrite ptr x =
atomicModifyIORef ptr (\ _ -> (x,()))
----------------------------------------------
-- functions operating on lists
-- we create a new list
newList :: IO (ListHandle a)
newList =
do null <- newIORef Null
hd <- newIORef (Head {next = null })
hdPtr <- newIORef hd
tailPtr <- newIORef null
return (ListHandle {headList = hdPtr, tailList = tailPtr})
-- we add a new node, by overwriting the null tail node
-- we only need to adjust tailList but not headList because
-- of the static Head
-- we return the location of the newly added node
addToTail :: Eq a => ListHandle a -> a -> IO ()
addToTail (ListHandle {tailList = tailPtrPtr}) x =
do null <- newIORef Null
repeatUntil
(do tailPtr <- readIORef tailPtrPtr
b <- atomCAS tailPtr Null (Node {val = x, next = null})
return b )
-- we atomically update the tail
-- (by spinning on the tailPtr)
atomicWrite tailPtrPtr null
find :: Eq a => ListHandle a -> a -> IO Bool
find (ListHandle { headList = head }) x =
let go !prevPtr =
do prevNode <- readIORef prevPtr
let curPtr = myNext prevNode -- head/node/delnode have all next
curNode <- readIORef curPtr
case curNode of
Node {val = y, next = nextNode } ->
if (x == y)
then -- node found and alive
return True
else go curPtr -- continue
Null -> return False -- reached end of list
DelNode {next = nextNode } ->
-- atomically delete curNode by setting the next of prevNode to next of curNode
-- if this fails we simply move ahead
case prevNode of
Node {} -> do b <- atomCAS prevPtr prevNode (Node {val = val prevNode,
next = nextNode})
if b then go prevPtr
else go curPtr
Head {} -> do b <- atomCAS prevPtr prevNode (Head {next = nextNode})
if b then go prevPtr
else go curPtr
DelNode {} -> go curPtr -- if parent deleted simply move ahead
{-
correct as well, but a deleted parent deleting a child is (for certain cases) a useless operation
do atomicModifyIORef prevPtr ( \ cur -> (cur{next = nextNode},True))
go prevPtr
-}
in do startPtr <- readIORef head
go startPtr
delete :: Eq a => ListHandle a -> a -> IO Bool
delete (ListHandle { headList = head }) x =
let go prevPtr =
do do prevNode <- readIORef prevPtr
let curPtr = next prevNode -- head/node/delnode have all next
curNode <- readIORef curPtr
case curNode of
Node {val = y, next = nextNode } ->
if (x == y)
then -- node found and alive
do b <- atomCAS curPtr curNode (DelNode {next = nextNode})
if b then return True
else go prevPtr -- spin
else go curPtr -- continue
Null -> return False -- reached end of list
DelNode {next = nextNode } ->
-- atomically delete curNode by setting the next of prevNode to next of curNode
-- if this fails we simply move ahead
case prevNode of
Node {} -> do b <- atomCAS prevPtr prevNode (Node {val = val prevNode,
next = nextNode})
if b then go prevPtr
else go curPtr
Head {} -> do b <- atomCAS prevPtr prevNode (Head {next = nextNode})
if b then go prevPtr
else go curPtr
DelNode {} -> go curPtr -- if parent deleted simply move ahead
in do startPtr <- readIORef head
go startPtr
-- the iterator always points to the PREVIOUS node,
-- recall that there's a static dummy new Head
-- Assumption: iterators are private,
-- ie they won't be shared among threads
newIterator :: ListHandle a -> IO (Iterator a)
newIterator (ListHandle {headList = hd}) =
do hdPtr <- readIORef hd
it <- newIORef hdPtr
return it
-- we iterate through the list and return the first "not deleted" node
-- we delink deleted nodes
-- there's no need to adjust headList, tailList
-- cause headList has a static Head and
-- tailList points to Null
iterateList :: Eq a => Iterator a -> IO (Maybe (IORef (List a)))
iterateList itPtrPtr =
let go prevPtr =
do do prevNode <- readIORef prevPtr
let curPtr = next prevNode -- head/node/delnode have all next
curNode <- readIORef curPtr
case curNode of
Node {} -> do writeIORef itPtrPtr curPtr
-- adjust iterator
return (Just curPtr)
Null -> return Nothing -- reached end of list
DelNode {next = nextNode} ->
-- atomically delete curNode by setting the next of prevNode to next of curNode
-- if this fails we simply move ahead
case prevNode of
Node {} -> do b <- atomCAS prevPtr prevNode (Node {val = val prevNode,
next = nextNode})
if b then go prevPtr
else go curPtr
Head {} -> do b <- atomCAS prevPtr prevNode (Head {next = nextNode})
if b then go prevPtr
else go curPtr
DelNode {} -> go curPtr -- if parent deleted simply move ahead
in do startPtr <- readIORef itPtrPtr
go startPtr
--printing and counting
printList :: Show a => ListHandle a -> IO ()
printList (ListHandle {headList = ptrPtr}) =
do startptr <- (
do ptr <- readIORef ptrPtr
Head {next = startptr} <- readIORef ptr
return startptr)
printListHelp startptr
printListHelp :: Show a => IORef (List a) -> IO ()
printListHelp curNodePtr =
do { curNode <- readIORef curNodePtr
; case curNode of
Null -> putStr "Nil"
Node {val = curval, next = curnext} ->
do { putStr (show curval ++ " -> ")
; printListHelp curnext }
DelNode {next = curnext} ->
do { putStr ("DEAD -> ")
; printListHelp curnext }
}
cntList :: Show a => ListHandle a -> IO Int
cntList (ListHandle {headList = ptrPtr}) =
do startptr <- (
do ptr <- readIORef ptrPtr
Head {next = startptr} <- readIORef ptr
return startptr)
cntListHelp startptr 0
cntListHelp :: Show a => IORef (List a) -> Int -> IO Int
cntListHelp curNodePtr i =
do { curNode <- readIORef curNodePtr
; case curNode of
Null -> return i
Node {val = curval, next = curnext} ->
cntListHelp curnext (i+1)
DelNode {next = curnext} ->
cntListHelp curnext (i+1)
}
|
