\begin{code}
{-# OPTIONS_GHC -fno-implicit-prelude #-}
-----------------------------------------------------------------------------
-- |
-- Module : GHC.Conc
-- Copyright : (c) The University of Glasgow, 1994-2002
-- License : see libraries/base/LICENSE
--
-- Maintainer : cvs-ghc@haskell.org
-- Stability : internal
-- Portability : non-portable (GHC extensions)
--
-- Basic concurrency stuff.
--
-----------------------------------------------------------------------------
-- No: #hide, because bits of this module are exposed by the stm package.
-- However, we don't want this module to be the home location for the
-- bits it exports, we'd rather have Control.Concurrent and the other
-- higher level modules be the home. Hence:
#include "Typeable.h"
-- #not-home
module GHC.Conc
( ThreadId(..)
-- * Forking and suchlike
, forkIO -- :: IO a -> IO ThreadId
, forkOnIO -- :: Int -> IO a -> IO ThreadId
, childHandler -- :: Exception -> IO ()
, myThreadId -- :: IO ThreadId
, killThread -- :: ThreadId -> IO ()
, throwTo -- :: ThreadId -> Exception -> IO ()
, par -- :: a -> b -> b
, pseq -- :: a -> b -> b
, yield -- :: IO ()
, labelThread -- :: ThreadId -> String -> IO ()
-- * Waiting
, threadDelay -- :: Int -> IO ()
, registerDelay -- :: Int -> IO (TVar Bool)
, threadWaitRead -- :: Int -> IO ()
, threadWaitWrite -- :: Int -> IO ()
-- * MVars
, MVar -- abstract
, newMVar -- :: a -> IO (MVar a)
, newEmptyMVar -- :: IO (MVar a)
, takeMVar -- :: MVar a -> IO a
, putMVar -- :: MVar a -> a -> IO ()
, tryTakeMVar -- :: MVar a -> IO (Maybe a)
, tryPutMVar -- :: MVar a -> a -> IO Bool
, isEmptyMVar -- :: MVar a -> IO Bool
, addMVarFinalizer -- :: MVar a -> IO () -> IO ()
-- * TVars
, STM -- abstract
, atomically -- :: STM a -> IO a
, retry -- :: STM a
, orElse -- :: STM a -> STM a -> STM a
, catchSTM -- :: STM a -> (Exception -> STM a) -> STM a
, alwaysSucceeds -- :: STM a -> STM ()
, always -- :: STM Bool -> STM ()
, TVar -- abstract
, newTVar -- :: a -> STM (TVar a)
, newTVarIO -- :: a -> STM (TVar a)
, readTVar -- :: TVar a -> STM a
, writeTVar -- :: a -> TVar a -> STM ()
, unsafeIOToSTM -- :: IO a -> STM a
-- * Miscellaneous
#ifdef mingw32_HOST_OS
, asyncRead -- :: Int -> Int -> Int -> Ptr a -> IO (Int, Int)
, asyncWrite -- :: Int -> Int -> Int -> Ptr a -> IO (Int, Int)
, asyncDoProc -- :: FunPtr (Ptr a -> IO Int) -> Ptr a -> IO Int
, asyncReadBA -- :: Int -> Int -> Int -> Int -> MutableByteArray# RealWorld -> IO (Int, Int)
, asyncWriteBA -- :: Int -> Int -> Int -> Int -> MutableByteArray# RealWorld -> IO (Int, Int)
#endif
, ensureIOManagerIsRunning
) where
import System.Posix.Types
#ifndef mingw32_HOST_OS
import System.Posix.Internals
#endif
import Foreign
import Foreign.C
#ifndef __HADDOCK__
import {-# SOURCE #-} GHC.TopHandler ( reportError, reportStackOverflow )
#endif
import Data.Maybe
import GHC.Base
import GHC.IOBase
import GHC.Num ( Num(..) )
import GHC.Real ( fromIntegral, div )
#ifndef mingw32_HOST_OS
import GHC.Base ( Int(..) )
#endif
import GHC.Exception ( catchException, Exception(..), AsyncException(..) )
import GHC.Pack ( packCString# )
import GHC.Ptr ( Ptr(..), plusPtr, FunPtr(..) )
import GHC.STRef
import GHC.Show ( Show(..), showString )
import Data.Typeable
infixr 0 `par`, `pseq`
\end{code}
%************************************************************************
%* *
\subsection{@ThreadId@, @par@, and @fork@}
%* *
%************************************************************************
\begin{code}
data ThreadId = ThreadId ThreadId# deriving( Typeable )
-- ToDo: data ThreadId = ThreadId (Weak ThreadId#)
-- But since ThreadId# is unlifted, the Weak type must use open
-- type variables.
{- ^
A 'ThreadId' is an abstract type representing a handle to a thread.
'ThreadId' is an instance of 'Eq', 'Ord' and 'Show', where
the 'Ord' instance implements an arbitrary total ordering over
'ThreadId's. The 'Show' instance lets you convert an arbitrary-valued
'ThreadId' to string form; showing a 'ThreadId' value is occasionally
useful when debugging or diagnosing the behaviour of a concurrent
program.
/Note/: in GHC, if you have a 'ThreadId', you essentially have
a pointer to the thread itself. This means the thread itself can\'t be
garbage collected until you drop the 'ThreadId'.
This misfeature will hopefully be corrected at a later date.
/Note/: Hugs does not provide any operations on other threads;
it defines 'ThreadId' as a synonym for ().
-}
instance Show ThreadId where
showsPrec d t =
showString "ThreadId " .
showsPrec d (getThreadId (id2TSO t))
foreign import ccall unsafe "rts_getThreadId" getThreadId :: ThreadId# -> CInt
id2TSO :: ThreadId -> ThreadId#
id2TSO (ThreadId t) = t
foreign import ccall unsafe "cmp_thread" cmp_thread :: ThreadId# -> ThreadId# -> CInt
-- Returns -1, 0, 1
cmpThread :: ThreadId -> ThreadId -> Ordering
cmpThread t1 t2 =
case cmp_thread (id2TSO t1) (id2TSO t2) of
-1 -> LT
0 -> EQ
_ -> GT -- must be 1
instance Eq ThreadId where
t1 == t2 =
case t1 `cmpThread` t2 of
EQ -> True
_ -> False
instance Ord ThreadId where
compare = cmpThread
{- |
This sparks off a new thread to run the 'IO' computation passed as the
first argument, and returns the 'ThreadId' of the newly created
thread.
The new thread will be a lightweight thread; if you want to use a foreign
library that uses thread-local storage, use 'forkOS' instead.
-}
forkIO :: IO () -> IO ThreadId
forkIO action = IO $ \ s ->
case (fork# action_plus s) of (# s1, id #) -> (# s1, ThreadId id #)
where
action_plus = catchException action childHandler
forkOnIO :: Int -> IO () -> IO ThreadId
forkOnIO (I# cpu) action = IO $ \ s ->
case (forkOn# cpu action_plus s) of (# s1, id #) -> (# s1, ThreadId id #)
where
action_plus = catchException action childHandler
childHandler :: Exception -> IO ()
childHandler err = catchException (real_handler err) childHandler
real_handler :: Exception -> IO ()
real_handler ex =
case ex of
-- ignore thread GC and killThread exceptions:
BlockedOnDeadMVar -> return ()
BlockedIndefinitely -> return ()
AsyncException ThreadKilled -> return ()
-- report all others:
AsyncException StackOverflow -> reportStackOverflow
other -> reportError other
{- | 'killThread' terminates the given thread (GHC only).
Any work already done by the thread isn\'t
lost: the computation is suspended until required by another thread.
The memory used by the thread will be garbage collected if it isn\'t
referenced from anywhere. The 'killThread' function is defined in
terms of 'throwTo':
> killThread tid = throwTo tid (AsyncException ThreadKilled)
-}
killThread :: ThreadId -> IO ()
killThread tid = throwTo tid (AsyncException ThreadKilled)
{- | 'throwTo' raises an arbitrary exception in the target thread (GHC only).
'throwTo' does not return until the exception has been raised in the
target thread.
The calling thread can thus be certain that the target
thread has received the exception. This is a useful property to know
when dealing with race conditions: eg. if there are two threads that
can kill each other, it is guaranteed that only one of the threads
will get to kill the other.
If the target thread is currently making a foreign call, then the
exception will not be raised (and hence 'throwTo' will not return)
until the call has completed. This is the case regardless of whether
the call is inside a 'block' or not.
Important note: the behaviour of 'throwTo' differs from that described in
the paper "Asynchronous exceptions in Haskell"
(<http://research.microsoft.com/~simonpj/Papers/asynch-exns.htm>).
In the paper, 'throwTo' is non-blocking; but the library implementation adopts
a more synchronous design in which 'throwTo' does not return until the exception
is received by the target thread. The trade-off is discussed in Section 8 of the paper.
Like any blocking operation, 'throwTo' is therefore interruptible (see Section 4.3 of
the paper).
There is currently no guarantee that the exception delivered by 'throwTo' will be
delivered at the first possible opportunity. In particular, if a thread may
unblock and then re-block exceptions (using 'unblock' and 'block') without receiving
a pending 'throwTo'. This is arguably undesirable behaviour.
-}
throwTo :: ThreadId -> Exception -> IO ()
throwTo (ThreadId id) ex = IO $ \ s ->
case (killThread# id ex s) of s1 -> (# s1, () #)
-- | Returns the 'ThreadId' of the calling thread (GHC only).
myThreadId :: IO ThreadId
myThreadId = IO $ \s ->
case (myThreadId# s) of (# s1, id #) -> (# s1, ThreadId id #)
-- |The 'yield' action allows (forces, in a co-operative multitasking
-- implementation) a context-switch to any other currently runnable
-- threads (if any), and is occasionally useful when implementing
-- concurrency abstractions.
yield :: IO ()
yield = IO $ \s ->
case (yield# s) of s1 -> (# s1, () #)
{- | 'labelThread' stores a string as identifier for this thread if
you built a RTS with debugging support. This identifier will be used in
the debugging output to make distinction of different threads easier
(otherwise you only have the thread state object\'s address in the heap).
Other applications like the graphical Concurrent Haskell Debugger
(<http://www.informatik.uni-kiel.de/~fhu/chd/>) may choose to overload
'labelThread' for their purposes as well.
-}
labelThread :: ThreadId -> String -> IO ()
labelThread (ThreadId t) str = IO $ \ s ->
let ps = packCString# str
adr = byteArrayContents# ps in
case (labelThread# t adr s) of s1 -> (# s1, () #)
-- Nota Bene: 'pseq' used to be 'seq'
-- but 'seq' is now defined in PrelGHC
--
-- "pseq" is defined a bit weirdly (see below)
--
-- The reason for the strange "lazy" call is that
-- it fools the compiler into thinking that pseq and par are non-strict in
-- their second argument (even if it inlines pseq at the call site).
-- If it thinks pseq is strict in "y", then it often evaluates
-- "y" before "x", which is totally wrong.
{-# INLINE pseq #-}
pseq :: a -> b -> b
pseq x y = x `seq` lazy y
{-# INLINE par #-}
par :: a -> b -> b
par x y = case (par# x) of { _ -> lazy y }
\end{code}
%************************************************************************
%* *
\subsection[stm]{Transactional heap operations}
%* *
%************************************************************************
TVars are shared memory locations which support atomic memory
transactions.
\begin{code}
-- |A monad supporting atomic memory transactions.
newtype STM a = STM (State# RealWorld -> (# State# RealWorld, a #))
unSTM :: STM a -> (State# RealWorld -> (# State# RealWorld, a #))
unSTM (STM a) = a
INSTANCE_TYPEABLE1(STM,stmTc,"STM")
instance Functor STM where
fmap f x = x >>= (return . f)
instance Monad STM where
{-# INLINE return #-}
{-# INLINE (>>) #-}
{-# INLINE (>>=) #-}
m >> k = thenSTM m k
return x = returnSTM x
m >>= k = bindSTM m k
bindSTM :: STM a -> (a -> STM b) -> STM b
bindSTM (STM m) k = STM ( \s ->
case m s of
(# new_s, a #) -> unSTM (k a) new_s
)
thenSTM :: STM a -> STM b -> STM b
thenSTM (STM m) k = STM ( \s ->
case m s of
(# new_s, a #) -> unSTM k new_s
)
returnSTM :: a -> STM a
returnSTM x = STM (\s -> (# s, x #))
-- | Unsafely performs IO in the STM monad.
unsafeIOToSTM :: IO a -> STM a
unsafeIOToSTM (IO m) = STM m
-- |Perform a series of STM actions atomically.
--
-- You cannot use 'atomically' inside an 'unsafePerformIO' or 'unsafeInterleaveIO'.
-- Any attempt to do so will result in a runtime error. (Reason: allowing
-- this would effectively allow a transaction inside a transaction, depending
-- on exactly when the thunk is evaluated.)
--
-- However, see 'newTVarIO', which can be called inside 'unsafePerformIO',
-- and which allows top-level TVars to be allocated.
atomically :: STM a -> IO a
atomically (STM m) = IO (\s -> (atomically# m) s )
-- |Retry execution of the current memory transaction because it has seen
-- values in TVars which mean that it should not continue (e.g. the TVars
-- represent a shared buffer that is now empty). The implementation may
-- block the thread until one of the TVars that it has read from has been
-- udpated. (GHC only)
retry :: STM a
retry = STM $ \s# -> retry# s#
-- |Compose two alternative STM actions (GHC only). If the first action
-- completes without retrying then it forms the result of the orElse.
-- Otherwise, if the first action retries, then the second action is
-- tried in its place. If both actions retry then the orElse as a
-- whole retries.
orElse :: STM a -> STM a -> STM a
orElse (STM m) e = STM $ \s -> catchRetry# m (unSTM e) s
-- |Exception handling within STM actions.
catchSTM :: STM a -> (Exception -> STM a) -> STM a
catchSTM (STM m) k = STM $ \s -> catchSTM# m (\ex -> unSTM (k ex)) s
-- | Low-level primitive on which always and alwaysSucceeds are built.
-- checkInv differs form these in that (i) the invariant is not
-- checked when checkInv is called, only at the end of this and
-- subsequent transcations, (ii) the invariant failure is indicated
-- by raising an exception.
checkInv :: STM a -> STM ()
checkInv (STM m) = STM (\s -> (check# m) s)
-- | alwaysSucceeds adds a new invariant that must be true when passed
-- to alwaysSucceeds, at the end of the current transaction, and at
-- the end of every subsequent transaction. If it fails at any
-- of those points then the transaction violating it is aborted
-- and the exception raised by the invariant is propagated.
alwaysSucceeds :: STM a -> STM ()
alwaysSucceeds i = do ( do i ; retry ) `orElse` ( return () )
checkInv i
-- | always is a variant of alwaysSucceeds in which the invariant is
-- expressed as an STM Bool action that must return True. Returning
-- False or raising an exception are both treated as invariant failures.
always :: STM Bool -> STM ()
always i = alwaysSucceeds ( do v <- i
if (v) then return () else ( error "Transacional invariant violation" ) )
-- |Shared memory locations that support atomic memory transactions.
data TVar a = TVar (TVar# RealWorld a)
INSTANCE_TYPEABLE1(TVar,tvarTc,"TVar")
instance Eq (TVar a) where
(TVar tvar1#) == (TVar tvar2#) = sameTVar# tvar1# tvar2#
-- |Create a new TVar holding a value supplied
newTVar :: a -> STM (TVar a)
newTVar val = STM $ \s1# ->
case newTVar# val s1# of
(# s2#, tvar# #) -> (# s2#, TVar tvar# #)
-- |@IO@ version of 'newTVar'. This is useful for creating top-level
-- 'TVar's using 'System.IO.Unsafe.unsafePerformIO', because using
-- 'atomically' inside 'System.IO.Unsafe.unsafePerformIO' isn't
-- possible.
newTVarIO :: a -> IO (TVar a)
newTVarIO val = IO $ \s1# ->
case newTVar# val s1# of
(# s2#, tvar# #) -> (# s2#, TVar tvar# #)
-- |Return the current value stored in a TVar
readTVar :: TVar a -> STM a
readTVar (TVar tvar#) = STM $ \s# -> readTVar# tvar# s#
-- |Write the supplied value into a TVar
writeTVar :: TVar a -> a -> STM ()
writeTVar (TVar tvar#) val = STM $ \s1# ->
case writeTVar# tvar# val s1# of
s2# -> (# s2#, () #)
\end{code}
%************************************************************************
%* *
\subsection[mvars]{M-Structures}
%* *
%************************************************************************
M-Vars are rendezvous points for concurrent threads. They begin
empty, and any attempt to read an empty M-Var blocks. When an M-Var
is written, a single blocked thread may be freed. Reading an M-Var
toggles its state from full back to empty. Therefore, any value
written to an M-Var may only be read once. Multiple reads and writes
are allowed, but there must be at least one read between any two
writes.
\begin{code}
--Defined in IOBase to avoid cycle: data MVar a = MVar (SynchVar# RealWorld a)
-- |Create an 'MVar' which is initially empty.
newEmptyMVar :: IO (MVar a)
newEmptyMVar = IO $ \ s# ->
case newMVar# s# of
(# s2#, svar# #) -> (# s2#, MVar svar# #)
-- |Create an 'MVar' which contains the supplied value.
newMVar :: a -> IO (MVar a)
newMVar value =
newEmptyMVar >>= \ mvar ->
putMVar mvar value >>
return mvar
-- |Return the contents of the 'MVar'. If the 'MVar' is currently
-- empty, 'takeMVar' will wait until it is full. After a 'takeMVar',
-- the 'MVar' is left empty.
--
-- There are two further important properties of 'takeMVar':
--
-- * 'takeMVar' is single-wakeup. That is, if there are multiple
-- threads blocked in 'takeMVar', and the 'MVar' becomes full,
-- only one thread will be woken up. The runtime guarantees that
-- the woken thread completes its 'takeMVar' operation.
--
-- * When multiple threads are blocked on an 'MVar', they are
-- woken up in FIFO order. This is useful for providing
-- fairness properties of abstractions built using 'MVar's.
--
takeMVar :: MVar a -> IO a
takeMVar (MVar mvar#) = IO $ \ s# -> takeMVar# mvar# s#
-- |Put a value into an 'MVar'. If the 'MVar' is currently full,
-- 'putMVar' will wait until it becomes empty.
--
-- There are two further important properties of 'putMVar':
--
-- * 'putMVar' is single-wakeup. That is, if there are multiple
-- threads blocked in 'putMVar', and the 'MVar' becomes empty,
-- only one thread will be woken up. The runtime guarantees that
-- the woken thread completes its 'putMVar' operation.
--
-- * When multiple threads are blocked on an 'MVar', they are
-- woken up in FIFO order. This is useful for providing
-- fairness properties of abstractions built using 'MVar's.
--
putMVar :: MVar a -> a -> IO ()
putMVar (MVar mvar#) x = IO $ \ s# ->
case putMVar# mvar# x s# of
s2# -> (# s2#, () #)
-- |A non-blocking version of 'takeMVar'. The 'tryTakeMVar' function
-- returns immediately, with 'Nothing' if the 'MVar' was empty, or
-- @'Just' a@ if the 'MVar' was full with contents @a@. After 'tryTakeMVar',
-- the 'MVar' is left empty.
tryTakeMVar :: MVar a -> IO (Maybe a)
tryTakeMVar (MVar m) = IO $ \ s ->
case tryTakeMVar# m s of
(# s, 0#, _ #) -> (# s, Nothing #) -- MVar is empty
(# s, _, a #) -> (# s, Just a #) -- MVar is full
-- |A non-blocking version of 'putMVar'. The 'tryPutMVar' function
-- attempts to put the value @a@ into the 'MVar', returning 'True' if
-- it was successful, or 'False' otherwise.
tryPutMVar :: MVar a -> a -> IO Bool
tryPutMVar (MVar mvar#) x = IO $ \ s# ->
case tryPutMVar# mvar# x s# of
(# s, 0# #) -> (# s, False #)
(# s, _ #) -> (# s, True #)
-- |Check whether a given 'MVar' is empty.
--
-- Notice that the boolean value returned is just a snapshot of
-- the state of the MVar. By the time you get to react on its result,
-- the MVar may have been filled (or emptied) - so be extremely
-- careful when using this operation. Use 'tryTakeMVar' instead if possible.
isEmptyMVar :: MVar a -> IO Bool
isEmptyMVar (MVar mv#) = IO $ \ s# ->
case isEmptyMVar# mv# s# of
(# s2#, flg #) -> (# s2#, not (flg ==# 0#) #)
-- |Add a finalizer to an 'MVar' (GHC only). See "Foreign.ForeignPtr" and
-- "System.Mem.Weak" for more about finalizers.
addMVarFinalizer :: MVar a -> IO () -> IO ()
addMVarFinalizer (MVar m) finalizer =
IO $ \s -> case mkWeak# m () finalizer s of { (# s1, w #) -> (# s1, () #) }
\end{code}
%************************************************************************
%* *
\subsection{Thread waiting}
%* *
%************************************************************************
\begin{code}
#ifdef mingw32_HOST_OS
-- Note: threadDelay, threadWaitRead and threadWaitWrite aren't really functional
-- on Win32, but left in there because lib code (still) uses them (the manner
-- in which they're used doesn't cause problems on a Win32 platform though.)
asyncRead :: Int -> Int -> Int -> Ptr a -> IO (Int, Int)
asyncRead (I# fd) (I# isSock) (I# len) (Ptr buf) =
IO $ \s -> case asyncRead# fd isSock len buf s of
(# s, len#, err# #) -> (# s, (I# len#, I# err#) #)
asyncWrite :: Int -> Int -> Int -> Ptr a -> IO (Int, Int)
asyncWrite (I# fd) (I# isSock) (I# len) (Ptr buf) =
IO $ \s -> case asyncWrite# fd isSock len buf s of
(# s, len#, err# #) -> (# s, (I# len#, I# err#) #)
asyncDoProc :: FunPtr (Ptr a -> IO Int) -> Ptr a -> IO Int
asyncDoProc (FunPtr proc) (Ptr param) =
-- the 'length' value is ignored; simplifies implementation of
-- the async*# primops to have them all return the same result.
IO $ \s -> case asyncDoProc# proc param s of
(# s, len#, err# #) -> (# s, I# err# #)
-- to aid the use of these primops by the IO Handle implementation,
-- provide the following convenience funs:
-- this better be a pinned byte array!
asyncReadBA :: Int -> Int -> Int -> Int -> MutableByteArray# RealWorld -> IO (Int,Int)
asyncReadBA fd isSock len off bufB =
asyncRead fd isSock len ((Ptr (byteArrayContents# (unsafeCoerce# bufB))) `plusPtr` off)
asyncWriteBA :: Int -> Int -> Int -> Int -> MutableByteArray# RealWorld -> IO (Int,Int)
asyncWriteBA fd isSock len off bufB =
asyncWrite fd isSock len ((Ptr (byteArrayContents# (unsafeCoerce# bufB))) `plusPtr` off)
#endif
-- -----------------------------------------------------------------------------
-- Thread IO API
-- | Block the current thread until data is available to read on the
-- given file descriptor (GHC only).
threadWaitRead :: Fd -> IO ()
threadWaitRead fd
#ifndef mingw32_HOST_OS
| threaded = waitForReadEvent fd
#endif
| otherwise = IO $ \s ->
case fromIntegral fd of { I# fd# ->
case waitRead# fd# s of { s -> (# s, () #)
}}
-- | Block the current thread until data can be written to the
-- given file descriptor (GHC only).
threadWaitWrite :: Fd -> IO ()
threadWaitWrite fd
#ifndef mingw32_HOST_OS
| threaded = waitForWriteEvent fd
#endif
| otherwise = IO $ \s ->
case fromIntegral fd of { I# fd# ->
case waitWrite# fd# s of { s -> (# s, () #)
}}
-- | Suspends the current thread for a given number of microseconds
-- (GHC only).
--
-- There is no guarantee that the thread will be rescheduled promptly
-- when the delay has expired, but the thread will never continue to
-- run /earlier/ than specified.
--
threadDelay :: Int -> IO ()
threadDelay time
| threaded = waitForDelayEvent time
| otherwise = IO $ \s ->
case fromIntegral time of { I# time# ->
case delay# time# s of { s -> (# s, () #)
}}
-- | Set the value of returned TVar to True after a given number of
-- microseconds. The caveats associated with threadDelay also apply.
--
registerDelay :: Int -> IO (TVar Bool)
registerDelay usecs
| threaded = waitForDelayEventSTM usecs
| otherwise = error "registerDelay: requires -threaded"
foreign import ccall unsafe "rtsSupportsBoundThreads" threaded :: Bool
waitForDelayEvent :: Int -> IO ()
waitForDelayEvent usecs = do
m <- newEmptyMVar
target <- calculateTarget usecs
atomicModifyIORef pendingDelays (\xs -> (Delay target m : xs, ()))
prodServiceThread
takeMVar m
-- Delays for use in STM
waitForDelayEventSTM :: Int -> IO (TVar Bool)
waitForDelayEventSTM usecs = do
t <- atomically $ newTVar False
target <- calculateTarget usecs
atomicModifyIORef pendingDelays (\xs -> (DelaySTM target t : xs, ()))
prodServiceThread
return t
calculateTarget :: Int -> IO USecs
calculateTarget usecs = do
now <- getUSecOfDay
return $ now + (fromIntegral usecs)
-- ----------------------------------------------------------------------------
-- Threaded RTS implementation of threadWaitRead, threadWaitWrite, threadDelay
-- In the threaded RTS, we employ a single IO Manager thread to wait
-- for all outstanding IO requests (threadWaitRead,threadWaitWrite)
-- and delays (threadDelay).
--
-- We can do this because in the threaded RTS the IO Manager can make
-- a non-blocking call to select(), so we don't have to do select() in
-- the scheduler as we have to in the non-threaded RTS. We get performance
-- benefits from doing it this way, because we only have to restart the select()
-- when a new request arrives, rather than doing one select() each time
-- around the scheduler loop. Furthermore, the scheduler can be simplified
-- by not having to check for completed IO requests.
-- Issues, possible problems:
--
-- - we might want bound threads to just do the blocking
-- operation rather than communicating with the IO manager
-- thread. This would prevent simgle-threaded programs which do
-- IO from requiring multiple OS threads. However, it would also
-- prevent bound threads waiting on IO from being killed or sent
-- exceptions.
--
-- - Apprently exec() doesn't work on Linux in a multithreaded program.
-- I couldn't repeat this.
--
-- - How do we handle signal delivery in the multithreaded RTS?
--
-- - forkProcess will kill the IO manager thread. Let's just
-- hope we don't need to do any blocking IO between fork & exec.
#ifndef mingw32_HOST_OS
data IOReq
= Read {-# UNPACK #-} !Fd {-# UNPACK #-} !(MVar ())
| Write {-# UNPACK #-} !Fd {-# UNPACK #-} !(MVar ())
#endif
data DelayReq
= Delay {-# UNPACK #-} !USecs {-# UNPACK #-} !(MVar ())
| DelaySTM {-# UNPACK #-} !USecs {-# UNPACK #-} !(TVar Bool)
#ifndef mingw32_HOST_OS
pendingEvents :: IORef [IOReq]
#endif
pendingDelays :: IORef [DelayReq]
-- could use a strict list or array here
{-# NOINLINE pendingEvents #-}
{-# NOINLINE pendingDelays #-}
(pendingEvents,pendingDelays) = unsafePerformIO $ do
startIOManagerThread
reqs <- newIORef []
dels <- newIORef []
return (reqs, dels)
-- the first time we schedule an IO request, the service thread
-- will be created (cool, huh?)
ensureIOManagerIsRunning :: IO ()
ensureIOManagerIsRunning
| threaded = seq pendingEvents $ return ()
| otherwise = return ()
insertDelay :: DelayReq -> [DelayReq] -> [DelayReq]
insertDelay d [] = [d]
insertDelay d1 ds@(d2 : rest)
| delayTime d1 <= delayTime d2 = d1 : ds
| otherwise = d2 : insertDelay d1 rest
delayTime :: DelayReq -> USecs
delayTime (Delay t _) = t
delayTime (DelaySTM t _) = t
type USecs = Word64
-- XXX: move into GHC.IOBase from Data.IORef?
atomicModifyIORef :: IORef a -> (a -> (a,b)) -> IO b
atomicModifyIORef (IORef (STRef r#)) f = IO $ \s -> atomicModifyMutVar# r# f s
foreign import ccall unsafe "getUSecOfDay"
getUSecOfDay :: IO USecs
prodding :: IORef Bool
{-# NOINLINE prodding #-}
prodding = unsafePerformIO (newIORef False)
prodServiceThread :: IO ()
prodServiceThread = do
was_set <- atomicModifyIORef prodding (\a -> (True,a))
if (not (was_set)) then wakeupIOManager else return ()
#ifdef mingw32_HOST_OS
-- ----------------------------------------------------------------------------
-- Windows IO manager thread
startIOManagerThread :: IO ()
startIOManagerThread = do
wakeup <- c_getIOManagerEvent
forkIO $ service_loop wakeup []
return ()
service_loop :: HANDLE -- read end of pipe
-> [DelayReq] -- current delay requests
-> IO ()
service_loop wakeup old_delays = do
-- pick up new delay requests
new_delays <- atomicModifyIORef pendingDelays (\a -> ([],a))
let delays = foldr insertDelay old_delays new_delays
now <- getUSecOfDay
(delays', timeout) <- getDelay now delays
r <- c_WaitForSingleObject wakeup timeout
case r of
0xffffffff -> do c_maperrno; throwErrno "service_loop"
0 -> do
r <- c_readIOManagerEvent
exit <-
case r of
_ | r == io_MANAGER_WAKEUP -> return False
_ | r == io_MANAGER_DIE -> return True
0 -> return False -- spurious wakeup
r -> do start_console_handler (r `shiftR` 1); return False
if exit
then return ()
else service_cont wakeup delays'
_other -> service_cont wakeup delays' -- probably timeout
service_cont wakeup delays = do
atomicModifyIORef prodding (\_ -> (False,False))
service_loop wakeup delays
-- must agree with rts/win32/ThrIOManager.c
io_MANAGER_WAKEUP = 0xffffffff :: Word32
io_MANAGER_DIE = 0xfffffffe :: Word32
start_console_handler :: Word32 -> IO ()
start_console_handler r = do
stableptr <- peek console_handler
forkIO $ do io <- deRefStablePtr stableptr; io (fromIntegral r)
return ()
foreign import ccall "&console_handler"
console_handler :: Ptr (StablePtr (CInt -> IO ()))
stick :: IORef HANDLE
{-# NOINLINE stick #-}
stick = unsafePerformIO (newIORef nullPtr)
wakeupIOManager = do
hdl <- readIORef stick
c_sendIOManagerEvent io_MANAGER_WAKEUP
-- Walk the queue of pending delays, waking up any that have passed
-- and return the smallest delay to wait for. The queue of pending
-- delays is kept ordered.
getDelay :: USecs -> [DelayReq] -> IO ([DelayReq], DWORD)
getDelay now [] = return ([], iNFINITE)
getDelay now all@(d : rest)
= case d of
Delay time m | now >= time -> do
putMVar m ()
getDelay now rest
DelaySTM time t | now >= time -> do
atomically $ writeTVar t True
getDelay now rest
_otherwise ->
-- delay is in millisecs for WaitForSingleObject
let micro_seconds = delayTime d - now
milli_seconds = (micro_seconds + 999) `div` 1000
in return (all, fromIntegral milli_seconds)
-- ToDo: this just duplicates part of System.Win32.Types, which isn't
-- available yet. We should move some Win32 functionality down here,
-- maybe as part of the grand reorganisation of the base package...
type HANDLE = Ptr ()
type DWORD = Word32
iNFINITE = 0xFFFFFFFF :: DWORD -- urgh
foreign import ccall unsafe "getIOManagerEvent" -- in the RTS (ThrIOManager.c)
c_getIOManagerEvent :: IO HANDLE
foreign import ccall unsafe "readIOManagerEvent" -- in the RTS (ThrIOManager.c)
c_readIOManagerEvent :: IO Word32
foreign import ccall unsafe "sendIOManagerEvent" -- in the RTS (ThrIOManager.c)
c_sendIOManagerEvent :: Word32 -> IO ()
foreign import ccall unsafe "maperrno" -- in Win32Utils.c
c_maperrno :: IO ()
foreign import stdcall "WaitForSingleObject"
c_WaitForSingleObject :: HANDLE -> DWORD -> IO DWORD
#else
-- ----------------------------------------------------------------------------
-- Unix IO manager thread, using select()
startIOManagerThread :: IO ()
startIOManagerThread = do
allocaArray 2 $ \fds -> do
throwErrnoIfMinus1 "startIOManagerThread" (c_pipe fds)
rd_end <- peekElemOff fds 0
wr_end <- peekElemOff fds 1
writeIORef stick (fromIntegral wr_end)
c_setIOManagerPipe wr_end
forkIO $ do
allocaBytes sizeofFdSet $ \readfds -> do
allocaBytes sizeofFdSet $ \writefds -> do
allocaBytes sizeofTimeVal $ \timeval -> do
service_loop (fromIntegral rd_end) readfds writefds timeval [] []
return ()
service_loop
:: Fd -- listen to this for wakeup calls
-> Ptr CFdSet
-> Ptr CFdSet
-> Ptr CTimeVal
-> [IOReq]
-> [DelayReq]
-> IO ()
service_loop wakeup readfds writefds ptimeval old_reqs old_delays = do
-- pick up new IO requests
new_reqs <- atomicModifyIORef pendingEvents (\a -> ([],a))
let reqs = new_reqs ++ old_reqs
-- pick up new delay requests
new_delays <- atomicModifyIORef pendingDelays (\a -> ([],a))
let delays = foldr insertDelay old_delays new_delays
-- build the FDSets for select()
fdZero readfds
fdZero writefds
fdSet wakeup readfds
maxfd <- buildFdSets 0 readfds writefds reqs
-- perform the select()
let do_select delays = do
-- check the current time and wake up any thread in
-- threadDelay whose timeout has expired. Also find the
-- timeout value for the select() call.
now <- getUSecOfDay
(delays', timeout) <- getDelay now ptimeval delays
res <- c_select (fromIntegral ((max wakeup maxfd)+1)) readfds writefds
nullPtr timeout
if (res == -1)
then do
err <- getErrno
case err of
_ | err == eINTR -> do_select delays'
-- EINTR: just redo the select()
_ | err == eBADF -> return (True, delays)
-- EBADF: one of the file descriptors is closed or bad,
-- we don't know which one, so wake everyone up.
_ | otherwise -> throwErrno "select"
-- otherwise (ENOMEM or EINVAL) something has gone
-- wrong; report the error.
else
return (False,delays')
(wakeup_all,delays') <- do_select delays
exit <-
if wakeup_all then return False
else do
b <- fdIsSet wakeup readfds
if b == 0
then return False
else alloca $ \p -> do
c_read (fromIntegral wakeup) p 1; return ()
s <- peek p
case s of
_ | s == io_MANAGER_WAKEUP -> return False
_ | s == io_MANAGER_DIE -> return True
_ -> do handler_tbl <- peek handlers
sp <- peekElemOff handler_tbl (fromIntegral s)
forkIO (do io <- deRefStablePtr sp; io)
return False
if exit then return () else do
atomicModifyIORef prodding (\_ -> (False,False))
reqs' <- if wakeup_all then do wakeupAll reqs; return []
else completeRequests reqs readfds writefds []
service_loop wakeup readfds writefds ptimeval reqs' delays'
io_MANAGER_WAKEUP = 0xff :: CChar
io_MANAGER_DIE = 0xfe :: CChar
stick :: IORef Fd
{-# NOINLINE stick #-}
stick = unsafePerformIO (newIORef 0)
wakeupIOManager :: IO ()
wakeupIOManager = do
fd <- readIORef stick
with io_MANAGER_WAKEUP $ \pbuf -> do
c_write (fromIntegral fd) pbuf 1; return ()
foreign import ccall "&signal_handlers" handlers :: Ptr (Ptr (StablePtr (IO ())))
foreign import ccall "setIOManagerPipe"
c_setIOManagerPipe :: CInt -> IO ()
-- -----------------------------------------------------------------------------
-- IO requests
buildFdSets maxfd readfds writefds [] = return maxfd
buildFdSets maxfd readfds writefds (Read fd m : reqs)
| fd >= fD_SETSIZE = error "buildFdSets: file descriptor out of range"
| otherwise = do
fdSet fd readfds
buildFdSets (max maxfd fd) readfds writefds reqs
buildFdSets maxfd readfds writefds (Write fd m : reqs)
| fd >= fD_SETSIZE = error "buildFdSets: file descriptor out of range"
| otherwise = do
fdSet fd writefds
buildFdSets (max maxfd fd) readfds writefds reqs
completeRequests [] _ _ reqs' = return reqs'
completeRequests (Read fd m : reqs) readfds writefds reqs' = do
b <- fdIsSet fd readfds
if b /= 0
then do putMVar m (); completeRequests reqs readfds writefds reqs'
else completeRequests reqs readfds writefds (Read fd m : reqs')
completeRequests (Write fd m : reqs) readfds writefds reqs' = do
b <- fdIsSet fd writefds
if b /= 0
then do putMVar m (); completeRequests reqs readfds writefds reqs'
else completeRequests reqs readfds writefds (Write fd m : reqs')
wakeupAll [] = return ()
wakeupAll (Read fd m : reqs) = do putMVar m (); wakeupAll reqs
wakeupAll (Write fd m : reqs) = do putMVar m (); wakeupAll reqs
waitForReadEvent :: Fd -> IO ()
waitForReadEvent fd = do
m <- newEmptyMVar
atomicModifyIORef pendingEvents (\xs -> (Read fd m : xs, ()))
prodServiceThread
takeMVar m
waitForWriteEvent :: Fd -> IO ()
waitForWriteEvent fd = do
m <- newEmptyMVar
atomicModifyIORef pendingEvents (\xs -> (Write fd m : xs, ()))
prodServiceThread
takeMVar m
-- -----------------------------------------------------------------------------
-- Delays
-- Walk the queue of pending delays, waking up any that have passed
-- and return the smallest delay to wait for. The queue of pending
-- delays is kept ordered.
getDelay :: USecs -> Ptr CTimeVal -> [DelayReq] -> IO ([DelayReq], Ptr CTimeVal)
getDelay now ptimeval [] = return ([],nullPtr)
getDelay now ptimeval all@(d : rest)
= case d of
Delay time m | now >= time -> do
putMVar m ()
getDelay now ptimeval rest
DelaySTM time t | now >= time -> do
atomically $ writeTVar t True
getDelay now ptimeval rest
_otherwise -> do
setTimevalTicks ptimeval (delayTime d - now)
return (all,ptimeval)
newtype CTimeVal = CTimeVal ()
foreign import ccall unsafe "sizeofTimeVal"
sizeofTimeVal :: Int
foreign import ccall unsafe "setTimevalTicks"
setTimevalTicks :: Ptr CTimeVal -> USecs -> IO ()
{-
On Win32 we're going to have a single Pipe, and a
waitForSingleObject with the delay time. For signals, we send a
byte down the pipe just like on Unix.
-}
-- ----------------------------------------------------------------------------
-- select() interface
-- ToDo: move to System.Posix.Internals?
newtype CFdSet = CFdSet ()
foreign import ccall safe "select"
c_select :: CInt -> Ptr CFdSet -> Ptr CFdSet -> Ptr CFdSet -> Ptr CTimeVal
-> IO CInt
foreign import ccall unsafe "hsFD_SETSIZE"
c_fD_SETSIZE :: CInt
fD_SETSIZE :: Fd
fD_SETSIZE = fromIntegral c_fD_SETSIZE
foreign import ccall unsafe "hsFD_CLR"
c_fdClr :: CInt -> Ptr CFdSet -> IO ()
fdClr :: Fd -> Ptr CFdSet -> IO ()
fdClr (Fd fd) fdset = c_fdClr fd fdset
foreign import ccall unsafe "hsFD_ISSET"
c_fdIsSet :: CInt -> Ptr CFdSet -> IO CInt
fdIsSet :: Fd -> Ptr CFdSet -> IO CInt
fdIsSet (Fd fd) fdset = c_fdIsSet fd fdset
foreign import ccall unsafe "hsFD_SET"
c_fdSet :: CInt -> Ptr CFdSet -> IO ()
fdSet :: Fd -> Ptr CFdSet -> IO ()
fdSet (Fd fd) fdset = c_fdSet fd fdset
foreign import ccall unsafe "hsFD_ZERO"
fdZero :: Ptr CFdSet -> IO ()
foreign import ccall unsafe "sizeof_fd_set"
sizeofFdSet :: Int
#endif
\end{code}
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