    {-# LANGUAGE MagicHash #-}
    {-# LANGUAGE NoImplicitPrelude #-}
    {-# LANGUAGE RankNTypes #-}
    {-# LANGUAGE UnboxedTuples #-}
    {-# LANGUAGE UnliftedFFITypes #-}
    {-# LANGUAGE KindSignatures #-}
    {-# LANGUAGE Unsafe #-}

    {-# OPTIONS_HADDOCK not-home #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  GHC.Internal.Conc.Sync
    -- Copyright   :  (c) The University of Glasgow, 1994-2002
    -- License     :  see libraries/base/LICENSE
    --
    -- Maintainer  :  ghc-devs@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:

    -- #not-home
    module GHC.Internal.Conc.Sync
            (
            -- * Threads
              ThreadId(..)
            , fromThreadId
            , showThreadId
            , myThreadId
            , killThread
            , throwTo
            , yield
            , labelThread
            , labelThreadByteArray#
            , mkWeakThreadId
            -- ** Queries
            , listThreads
            , threadLabel
            , ThreadStatus(..), BlockReason(..)
            , threadStatus
            , threadCapability

            -- * Forking and suchlike
            , forkIO
            , forkIOWithUnmask
            , forkOn
            , forkOnWithUnmask

            -- * Capabilities
            , numCapabilities
            , getNumCapabilities
            , setNumCapabilities
            , getNumProcessors

            -- * Sparks
            , numSparks
            , childHandler
            , par
            , pseq
            , runSparks

            -- * PrimMVar
            , newStablePtrPrimMVar, PrimMVar

            -- * Allocation counter and quota
            , setAllocationCounter
            , getAllocationCounter
            , enableAllocationLimit
            , disableAllocationLimit

            -- * TVars
            , STM(..)
            , atomically
            , retry
            , orElse
            , throwSTM
            , catchSTM
            , TVar(..)
            , newTVar
            , newTVarIO
            , readTVar
            , readTVarIO
            , writeTVar
            , unsafeIOToSTM

            -- * Miscellaneous
            , withMVar
            , modifyMVar_

            , setUncaughtExceptionHandler
            , getUncaughtExceptionHandler

            , reportError, reportStackOverflow, reportHeapOverflow

            , sharedCAF
            ) where

    import GHC.Internal.Foreign.C.Types
    import GHC.Internal.Foreign.C.String
    import GHC.Internal.Foreign.Storable
    import GHC.Internal.Foreign.StablePtr

    import GHC.Internal.Base
    import {-# SOURCE #-} GHC.Internal.IO.Handle ( hFlush )
    import {-# SOURCE #-} GHC.Internal.IO.StdHandles ( stdout )
    import GHC.Internal.Encoding.UTF8
    import GHC.Internal.Int
    import GHC.Internal.IO
    import GHC.Internal.IO.Exception
    import GHC.Internal.Exception
    import GHC.Internal.IORef
    import GHC.Internal.MVar
    import GHC.Internal.Ptr
    import GHC.Internal.Real         ( fromIntegral )
    import GHC.Internal.Show         ( Show(..), showParen, showString )
    import GHC.Internal.Weak
    import GHC.Internal.Word

    infixr 0 `par`, `pseq`

    -----------------------------------------------------------------------------
    -- 'ThreadId', 'par', and 'fork'
    -----------------------------------------------------------------------------

    data ThreadId = ThreadId ThreadId#
    {- ^
    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 would
    be difficult to correct while continuing to support 'threadStatus'.
    -}

    -- | Map a thread to an integer identifier which is unique within the
    -- current process.
    --
    -- @since base-4.19.0.0
    fromThreadId :: ThreadId -> Word64
    fromThreadId :: ThreadId -> Word64
    fromThreadId ThreadId
    tid = CULLong -> Word64
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral (CULLong -> Word64) -> CULLong -> Word64
    forall a b. (a -> b) -> a -> b
    $ ThreadId# -> CULLong
    getThreadId (ThreadId -> ThreadId#
    id2TSO ThreadId
    tid)

    -- | @since base-4.2.0.0
    instance Show ThreadId where
       showsPrec :: Int -> ThreadId -> ShowS
    showsPrec Int
    d ThreadId
    t = Bool -> ShowS -> ShowS
    showParen (Int
    d Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    >= Int
    11) (ShowS -> ShowS) -> ShowS -> ShowS
    forall a b. (a -> b) -> a -> b
    $
            String -> ShowS
    showString String
    "ThreadId " ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    .
            Int -> Word64 -> ShowS
    forall a. Show a => Int -> a -> ShowS
    showsPrec Int
    d (ThreadId -> Word64
    fromThreadId ThreadId
    t)

    showThreadId :: ThreadId -> String
    showThreadId :: ThreadId -> String
    showThreadId = ThreadId -> String
    forall a. Show a => a -> String
    show

    foreign import ccall unsafe "rts_getThreadId" getThreadId :: ThreadId# -> CULLong

    id2TSO :: ThreadId -> ThreadId#
    id2TSO :: ThreadId -> ThreadId#
    id2TSO (ThreadId ThreadId#
    t) = ThreadId#
    t

    foreign import ccall unsafe "eq_thread" eq_thread :: ThreadId# -> ThreadId# -> CBool

    foreign import ccall unsafe "cmp_thread" cmp_thread :: ThreadId# -> ThreadId# -> CInt
    -- Returns -1, 0, 1

    -- | @since base-4.2.0.0
    instance Eq ThreadId where
      ThreadId ThreadId#
    t1 == :: ThreadId -> ThreadId -> Bool
    == ThreadId ThreadId#
    t2 = ThreadId# -> ThreadId# -> CBool
    eq_thread ThreadId#
    t1 ThreadId#
    t2 CBool -> CBool -> Bool
    forall a. Eq a => a -> a -> Bool
    /= CBool
    0

    -- | @since base-4.2.0.0
    instance Ord ThreadId where
      compare :: ThreadId -> ThreadId -> Ordering
    compare (ThreadId ThreadId#
    t1) (ThreadId ThreadId#
    t2) = case ThreadId# -> ThreadId# -> CInt
    cmp_thread ThreadId#
    t1 ThreadId#
    t2 of
        -1 -> Ordering
    LT
        CInt
    0  -> Ordering
    EQ
        CInt
    _  -> Ordering
    GT

    -- | Every thread has an allocation counter that tracks how much
    -- memory has been allocated by the thread.  The counter is
    -- initialized to zero, and 'setAllocationCounter' sets the current
    -- value.  The allocation counter counts *down*, so in the absence of
    -- a call to 'setAllocationCounter' its value is the negation of the
    -- number of bytes of memory allocated by the thread.
    --
    -- There are two things that you can do with this counter:
    --
    -- * Use it as a simple profiling mechanism, with
    --   'getAllocationCounter'.
    --
    -- * Use it as a resource limit.  See 'enableAllocationLimit'.
    --
    -- Allocation accounting is accurate only to about 4Kbytes.
    --
    -- @since base-4.8.0.0
    setAllocationCounter :: Int64 -> IO ()
    setAllocationCounter :: Int64 -> IO ()
    setAllocationCounter (I64# Int64#
    i) = (State# RealWorld -> (# State# RealWorld, () #)) -> IO ()
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, () #)) -> IO ())
    -> (State# RealWorld -> (# State# RealWorld, () #)) -> IO ()
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s ->
      case Int64# -> State# RealWorld -> State# RealWorld
    setThreadAllocationCounter# Int64#
    i State# RealWorld
    s of State# RealWorld
    s' -> (# State# RealWorld
    s', () #)

    -- | Return the current value of the allocation counter for the
    -- current thread.
    --
    -- @since base-4.8.0.0
    getAllocationCounter :: IO Int64
    getAllocationCounter :: IO Int64
    getAllocationCounter = (State# RealWorld -> (# State# RealWorld, Int64 #)) -> IO Int64
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, Int64 #)) -> IO Int64)
    -> (State# RealWorld -> (# State# RealWorld, Int64 #)) -> IO Int64
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s ->
      case State# RealWorld -> (# State# RealWorld, Int64# #)
    getThreadAllocationCounter# State# RealWorld
    s of (# State# RealWorld
    s', Int64#
    ctr #) -> (# State# RealWorld
    s', Int64# -> Int64
    I64# Int64#
    ctr #)

    -- | Enables the allocation counter to be treated as a limit for the
    -- current thread.  When the allocation limit is enabled, if the
    -- allocation counter counts down below zero, the thread will be sent
    -- the 'AllocationLimitExceeded' asynchronous exception.  When this
    -- happens, the counter is reinitialised (by default
    -- to 100K, but tunable with the @+RTS -xq@ option) so that it can handle
    -- the exception and perform any necessary clean up.  If it exhausts
    -- this additional allowance, another 'AllocationLimitExceeded' exception
    -- is sent, and so forth.  Like other asynchronous exceptions, the
    -- 'AllocationLimitExceeded' exception is deferred while the thread is inside
    -- 'mask' or an exception handler in 'catch'.
    --
    -- Note that memory allocation is unrelated to /live memory/, also
    -- known as /heap residency/.  A thread can allocate a large amount of
    -- memory and retain anything between none and all of it.  It is
    -- better to think of the allocation limit as a limit on
    -- /CPU time/, rather than a limit on memory.
    --
    -- Compared to using timeouts, allocation limits don't count time
    -- spent blocked or in foreign calls.
    --
    -- @since base-4.8.0.0
    enableAllocationLimit :: IO ()
    enableAllocationLimit :: IO ()
    enableAllocationLimit = do
      ThreadId t <- IO ThreadId
    myThreadId
      rts_enableThreadAllocationLimit t

    -- | Disable allocation limit processing for the current thread.
    --
    -- @since base-4.8.0.0
    disableAllocationLimit :: IO ()
    disableAllocationLimit :: IO ()
    disableAllocationLimit = do
      ThreadId t <- IO ThreadId
    myThreadId
      rts_disableThreadAllocationLimit t

    foreign import ccall unsafe "rts_enableThreadAllocationLimit"
      rts_enableThreadAllocationLimit :: ThreadId# -> IO ()

    foreign import ccall unsafe "rts_disableThreadAllocationLimit"
      rts_disableThreadAllocationLimit :: ThreadId# -> IO ()

    {- |
    Creates 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, /unbound/ thread.  Foreign calls
    made by this thread are not guaranteed to be made by any particular OS
    thread; if you need foreign calls to be made by a particular OS
    thread, then use 'Control.Concurrent.forkOS' instead.

    The new thread inherits the /masked/ state of the parent (see
    'GHC.Control.Exception.mask').

    The newly created thread has an exception handler that discards the
    exceptions 'BlockedIndefinitelyOnMVar', 'BlockedIndefinitelyOnSTM', and
    'ThreadKilled', and passes all other exceptions to the uncaught
    exception handler.

    WARNING: Exceptions in the new thread will not be rethrown in the thread that
    created it. This means that you might be completely unaware of the problem
    if/when this happens.  You may want to use the
    <https://hackage.haskell.org/package/async async> library instead.
    -}
    forkIO :: IO () -> IO ThreadId
    forkIO :: IO () -> IO ThreadId
    forkIO IO ()
    action = (State# RealWorld -> (# State# RealWorld, ThreadId #))
    -> IO ThreadId
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, ThreadId #))
     -> IO ThreadId)
    -> (State# RealWorld -> (# State# RealWorld, ThreadId #))
    -> IO ThreadId
    forall a b. (a -> b) -> a -> b
    $ \ State# RealWorld
    s ->
       case ((State# RealWorld -> (# State# RealWorld, () #))
    -> State# RealWorld -> (# State# RealWorld, ThreadId# #)
    forall a.
    (State# RealWorld -> (# State# RealWorld, a #))
    -> State# RealWorld -> (# State# RealWorld, ThreadId# #)
    fork# (IO () -> State# RealWorld -> (# State# RealWorld, () #)
    forall a. IO a -> State# RealWorld -> (# State# RealWorld, a #)
    unIO IO ()
    action_plus) State# RealWorld
    s) of (# State# RealWorld
    s1, ThreadId#
    tid #) -> (# State# RealWorld
    s1, ThreadId# -> ThreadId
    ThreadId ThreadId#
    tid #)
     where
      -- We must use 'catch' rather than 'catchException' because the action
      -- could be bottom. #13330
      action_plus :: IO ()
    action_plus = IO () -> (SomeException -> IO ()) -> IO ()
    forall e a. Exception e => IO a -> (e -> IO a) -> IO a
    catch IO ()
    action SomeException -> IO ()
    childHandler

    -- | Like 'forkIO', but the child thread is passed a function that can
    -- be used to unmask asynchronous exceptions.  This function is
    -- typically used in the following way
    --
    -- >  ... mask_ $ forkIOWithUnmask $ \unmask ->
    -- >                 catch (unmask ...) handler
    --
    -- so that the exception handler in the child thread is established
    -- with asynchronous exceptions masked, meanwhile the main body of
    -- the child thread is executed in the unmasked state.
    --
    -- Note that the unmask function passed to the child thread should
    -- only be used in that thread; the behaviour is undefined if it is
    -- invoked in a different thread.
    --
    -- @since base-4.4.0.0
    forkIOWithUnmask :: ((forall a . IO a -> IO a) -> IO ()) -> IO ThreadId
    forkIOWithUnmask :: ((forall a. IO a -> IO a) -> IO ()) -> IO ThreadId
    forkIOWithUnmask (forall a. IO a -> IO a) -> IO ()
    io = IO () -> IO ThreadId
    forkIO ((forall a. IO a -> IO a) -> IO ()
    io IO a -> IO a
    forall a. IO a -> IO a
    unsafeUnmask)

    {- |
    Like 'forkIO', but lets you specify on which capability the thread
    should run.  Unlike a `forkIO` thread, a thread created by `forkOn`
    will stay on the same capability for its entire lifetime (`forkIO`
    threads can migrate between capabilities according to the scheduling
    policy).  `forkOn` is useful for overriding the scheduling policy when
    you know in advance how best to distribute the threads.

    The `Int` argument specifies a /capability number/ (see
    'getNumCapabilities').  Typically capabilities correspond to physical
    processors, but the exact behaviour is implementation-dependent.  The
    value passed to 'forkOn' is interpreted modulo the total number of
    capabilities as returned by 'getNumCapabilities'.

    GHC note: the number of capabilities is specified by the @+RTS -N@
    option when the program is started.  Capabilities can be fixed to
    actual processor cores with @+RTS -qa@ if the underlying operating
    system supports that, although in practice this is usually unnecessary
    (and may actually degrade performance in some cases - experimentation
    is recommended).

    @since base-4.4.0.0
    -}
    forkOn :: Int -> IO () -> IO ThreadId
    forkOn :: Int -> IO () -> IO ThreadId
    forkOn (I# Int#
    cpu) IO ()
    action = (State# RealWorld -> (# State# RealWorld, ThreadId #))
    -> IO ThreadId
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, ThreadId #))
     -> IO ThreadId)
    -> (State# RealWorld -> (# State# RealWorld, ThreadId #))
    -> IO ThreadId
    forall a b. (a -> b) -> a -> b
    $ \ State# RealWorld
    s ->
       case (Int#
    -> (State# RealWorld -> (# State# RealWorld, () #))
    -> State# RealWorld
    -> (# State# RealWorld, ThreadId# #)
    forall a.
    Int#
    -> (State# RealWorld -> (# State# RealWorld, a #))
    -> State# RealWorld
    -> (# State# RealWorld, ThreadId# #)
    forkOn# Int#
    cpu (IO () -> State# RealWorld -> (# State# RealWorld, () #)
    forall a. IO a -> State# RealWorld -> (# State# RealWorld, a #)
    unIO IO ()
    action_plus) State# RealWorld
    s) of (# State# RealWorld
    s1, ThreadId#
    tid #) -> (# State# RealWorld
    s1, ThreadId# -> ThreadId
    ThreadId ThreadId#
    tid #)
     where
      -- We must use 'catch' rather than 'catchException' because the action
      -- could be bottom. #13330
      action_plus :: IO ()
    action_plus = IO () -> (SomeException -> IO ()) -> IO ()
    forall e a. Exception e => IO a -> (e -> IO a) -> IO a
    catch IO ()
    action SomeException -> IO ()
    childHandler

    -- | Like 'forkIOWithUnmask', but the child thread is pinned to the
    -- given CPU, as with 'forkOn'.
    --
    -- @since base-4.4.0.0
    forkOnWithUnmask :: Int -> ((forall a . IO a -> IO a) -> IO ()) -> IO ThreadId
    forkOnWithUnmask :: Int -> ((forall a. IO a -> IO a) -> IO ()) -> IO ThreadId
    forkOnWithUnmask Int
    cpu (forall a. IO a -> IO a) -> IO ()
    io = Int -> IO () -> IO ThreadId
    forkOn Int
    cpu ((forall a. IO a -> IO a) -> IO ()
    io IO a -> IO a
    forall a. IO a -> IO a
    unsafeUnmask)

    -- | the value passed to the @+RTS -N@ flag.  This is the number of
    -- Haskell threads that can run truly simultaneously at any given
    -- time, and is typically set to the number of physical processor cores on
    -- the machine.
    --
    -- Strictly speaking it is better to use 'getNumCapabilities', because
    -- the number of capabilities might vary at runtime.
    --
    numCapabilities :: Int
    numCapabilities :: Int
    numCapabilities = IO Int -> Int
    forall a. IO a -> a
    unsafePerformIO (IO Int -> Int) -> IO Int -> Int
    forall a b. (a -> b) -> a -> b
    $ IO Int
    getNumCapabilities

    {- |
    Returns the number of Haskell threads that can run truly
    simultaneously (on separate physical processors) at any given time.  To change
    this value, use 'setNumCapabilities'.

    @since base-4.4.0.0
    -}
    getNumCapabilities :: IO Int
    getNumCapabilities :: IO Int
    getNumCapabilities = do
       n <- Ptr Word32 -> IO Word32
    forall a. Storable a => Ptr a -> IO a
    peek Ptr Word32
    enabled_capabilities
       return (fromIntegral n)

    {- |
    Set the number of Haskell threads that can run truly simultaneously
    (on separate physical processors) at any given time.  The number
    passed to `forkOn` is interpreted modulo this value.  The initial
    value is given by the @+RTS -N@ runtime flag.

    This is also the number of threads that will participate in parallel
    garbage collection.  It is strongly recommended that the number of
    capabilities is not set larger than the number of physical processor
    cores, and it may often be beneficial to leave one or more cores free
    to avoid contention with other processes in the machine.

    @since base-4.5.0.0
    -}
    setNumCapabilities :: Int -> IO ()
    setNumCapabilities :: Int -> IO ()
    setNumCapabilities Int
    i
      | Int
    i Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    <= Int
    0    = String -> IO ()
    forall a. String -> IO a
    failIO (String -> IO ()) -> String -> IO ()
    forall a b. (a -> b) -> a -> b
    $ String
    "setNumCapabilities: Capability count ("String -> ShowS
    forall a. [a] -> [a] -> [a]
    ++Int -> String
    forall a. Show a => a -> String
    show Int
    iString -> ShowS
    forall a. [a] -> [a] -> [a]
    ++String
    ") must be positive"
      | Bool
    otherwise = CUInt -> IO ()
    c_setNumCapabilities (Int -> CUInt
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral Int
    i)

    foreign import ccall safe "setNumCapabilities"
      c_setNumCapabilities :: CUInt -> IO ()

    -- | Returns the number of CPUs that the machine has
    --
    -- @since base-4.5.0.0
    getNumProcessors :: IO Int
    getNumProcessors :: IO Int
    getNumProcessors = (Word32 -> Int) -> IO Word32 -> IO Int
    forall a b. (a -> b) -> IO a -> IO b
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    fmap Word32 -> Int
    forall a b. (Integral a, Num b) => a -> b
    fromIntegral IO Word32
    c_getNumberOfProcessors

    foreign import ccall unsafe "getNumberOfProcessors"
      c_getNumberOfProcessors :: IO Word32

    -- | Returns the number of sparks currently in the local spark pool
    numSparks :: IO Int
    numSparks :: IO Int
    numSparks = (State# RealWorld -> (# State# RealWorld, Int #)) -> IO Int
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, Int #)) -> IO Int)
    -> (State# RealWorld -> (# State# RealWorld, Int #)) -> IO Int
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s -> case State# RealWorld -> (# State# RealWorld, Int# #)
    forall d. State# d -> (# State# d, Int# #)
    numSparks# State# RealWorld
    s of (# State# RealWorld
    s', Int#
    n #) -> (# State# RealWorld
    s', Int# -> Int
    I# Int#
    n #)

    foreign import ccall "&enabled_capabilities"
      enabled_capabilities :: Ptr Word32

    childHandler :: SomeException -> IO ()
    childHandler :: SomeException -> IO ()
    childHandler SomeException
    err = IO () -> (SomeException -> IO ()) -> IO ()
    forall e a. Exception e => IO a -> (e -> IO a) -> IO a
    catch (SomeException -> IO ()
    real_handler SomeException
    err) SomeException -> IO ()
    childHandler
      -- We must use catch here rather than catchException. If the
      -- raised exception throws an (imprecise) exception, then real_handler err
      -- will do so as well. If we use catchException here, then we could miss
      -- that exception.

    real_handler :: SomeException -> IO ()
    real_handler :: SomeException -> IO ()
    real_handler SomeException
    se
      | Just BlockedIndefinitelyOnMVar
    BlockedIndefinitelyOnMVar <- SomeException -> Maybe BlockedIndefinitelyOnMVar
    forall e. Exception e => SomeException -> Maybe e
    fromException SomeException
    se  =  () -> IO ()
    forall a. a -> IO a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()
      | Just BlockedIndefinitelyOnSTM
    BlockedIndefinitelyOnSTM  <- SomeException -> Maybe BlockedIndefinitelyOnSTM
    forall e. Exception e => SomeException -> Maybe e
    fromException SomeException
    se  =  () -> IO ()
    forall a. a -> IO a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()
      | Just AsyncException
    ThreadKilled              <- SomeException -> Maybe AsyncException
    forall e. Exception e => SomeException -> Maybe e
    fromException SomeException
    se  =  () -> IO ()
    forall a. a -> IO a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()
      | Just AsyncException
    StackOverflow             <- SomeException -> Maybe AsyncException
    forall e. Exception e => SomeException -> Maybe e
    fromException SomeException
    se  =  IO ()
    reportStackOverflow
      | Bool
    otherwise                                           =  SomeException -> IO ()
    reportError SomeException
    se

    {- | 'killThread' raises the 'ThreadKilled' exception in the given
    thread (GHC only).

    > killThread tid = throwTo tid ThreadKilled

    -}
    killThread :: ThreadId -> IO ()
    killThread :: ThreadId -> IO ()
    killThread ThreadId
    tid = ThreadId -> AsyncException -> IO ()
    forall e. Exception e => ThreadId -> e -> IO ()
    throwTo ThreadId
    tid AsyncException
    ThreadKilled

    {- | 'throwTo' raises an arbitrary exception in the target thread (GHC only).

    Exception delivery synchronizes between the source and target thread:
    '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.  Exception delivery is also atomic
    with respect to other exceptions. Atomicity is a useful property to have
    when dealing with race conditions: e.g. 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.

    Whatever work the target thread was doing when the exception was
    raised is not lost: the computation is suspended until required by
    another thread.

    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 'mask' or not.  However, in GHC a foreign call
    can be annotated as @interruptible@, in which case a 'throwTo' will
    cause the RTS to attempt to cause the call to return; see the GHC
    documentation for more details.

    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 9 of the paper.
    Like any blocking operation, 'throwTo' is therefore interruptible (see Section 5.3 of
    the paper).  Unlike other interruptible operations, however, 'throwTo'
    is /always/ interruptible, even if it does not actually block.

    There is no guarantee that the exception will be delivered promptly,
    although the runtime will endeavour to ensure that arbitrary
    delays don't occur.  In GHC, an exception can only be raised when a
    thread reaches a /safe point/, where a safe point is where memory
    allocation occurs.  Some loops do not perform any memory allocation
    inside the loop and therefore cannot be interrupted by a 'throwTo'.

    If the target of 'throwTo' is the calling thread, then the behaviour
    is the same as 'GHC.Internal.Control.Exception.throwIO', except that the exception
    is thrown as an asynchronous exception.  This means that if there is
    an enclosing pure computation, which would be the case if the current
    IO operation is inside 'unsafePerformIO' or 'unsafeInterleaveIO', that
    computation is not permanently replaced by the exception, but is
    suspended as if it had received an asynchronous exception.

    Note that if 'throwTo' is called with the current thread as the
    target, the exception will be thrown even if the thread is currently
    inside 'mask' or 'uninterruptibleMask'.
      -}
    throwTo :: Exception e => ThreadId -> e -> IO ()
    throwTo :: forall e. Exception e => ThreadId -> e -> IO ()
    throwTo (ThreadId ThreadId#
    tid) e
    ex = (State# RealWorld -> (# State# RealWorld, () #)) -> IO ()
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, () #)) -> IO ())
    -> (State# RealWorld -> (# State# RealWorld, () #)) -> IO ()
    forall a b. (a -> b) -> a -> b
    $ \ State# RealWorld
    s ->
       case (ThreadId# -> SomeException -> State# RealWorld -> State# RealWorld
    forall a. ThreadId# -> a -> State# RealWorld -> State# RealWorld
    killThread# ThreadId#
    tid (e -> SomeException
    forall e. Exception e => e -> SomeException
    toException e
    ex) State# RealWorld
    s) of State# RealWorld
    s1 -> (# State# RealWorld
    s1, () #)

    -- | Returns the 'ThreadId' of the calling thread (GHC only).
    myThreadId :: IO ThreadId
    myThreadId :: IO ThreadId
    myThreadId = (State# RealWorld -> (# State# RealWorld, ThreadId #))
    -> IO ThreadId
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, ThreadId #))
     -> IO ThreadId)
    -> (State# RealWorld -> (# State# RealWorld, ThreadId #))
    -> IO ThreadId
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s ->
       case (State# RealWorld -> (# State# RealWorld, ThreadId# #)
    myThreadId# State# RealWorld
    s) of (# State# RealWorld
    s1, ThreadId#
    tid #) -> (# State# RealWorld
    s1, ThreadId# -> ThreadId
    ThreadId ThreadId#
    tid #)

    -- | 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 ()
    yield = (State# RealWorld -> (# State# RealWorld, () #)) -> IO ()
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, () #)) -> IO ())
    -> (State# RealWorld -> (# State# RealWorld, () #)) -> IO ()
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s ->
       case (State# RealWorld -> State# RealWorld
    yield# State# RealWorld
    s) of State# RealWorld
    s1 -> (# State# RealWorld
    s1, () #)

    {- | 'labelThread' stores a string as identifier for this thread. 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). It also emits an event to the RTS eventlog.
    -}
    labelThread :: ThreadId -> String -> IO ()
    labelThread :: ThreadId -> String -> IO ()
    labelThread ThreadId
    t String
    str =
        ThreadId -> ByteArray# -> IO ()
    labelThreadByteArray# ThreadId
    t (String -> ByteArray#
    utf8EncodeByteArray# String
    str)

    -- | 'labelThreadByteArray#' sets the label of a thread to the given UTF-8
    --  encoded string contained in a `ByteArray#`.
    --
    --  @since base-4.18
    labelThreadByteArray# :: ThreadId -> ByteArray# -> IO ()
    labelThreadByteArray# :: ThreadId -> ByteArray# -> IO ()
    labelThreadByteArray# (ThreadId ThreadId#
    t) ByteArray#
    str =
        (State# RealWorld -> (# State# RealWorld, () #)) -> IO ()
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, () #)) -> IO ())
    -> (State# RealWorld -> (# State# RealWorld, () #)) -> IO ()
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s -> case ThreadId# -> ByteArray# -> State# RealWorld -> State# RealWorld
    labelThread# ThreadId#
    t ByteArray#
    str State# RealWorld
    s of State# RealWorld
    s1 -> (# State# RealWorld
    s1, () #)

    --      Nota Bene: 'pseq' used to be 'seq'
    --                 but 'seq' is now defined in GHC.Internal.Prim
    --
    -- "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 :: forall a b. a -> b -> b
    pseq  a
    x b
    y = a
    x a -> b -> b
    forall a b. a -> b -> b
    `seq` b -> b
    forall a. a -> a
    lazy b
    y

    {-# INLINE par  #-}
    par :: a -> b -> b
    par :: forall a b. a -> b -> b
    par  a
    x b
    y = case (a -> Int#
    forall a. a -> Int#
    par# a
    x) of { Int#
    _ -> b -> b
    forall a. a -> a
    lazy b
    y }

    -- | Internal function used by the RTS to run sparks.
    runSparks :: IO ()
    runSparks :: IO ()
    runSparks = (State# RealWorld -> (# State# RealWorld, () #)) -> IO ()
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO State# RealWorld -> (# State# RealWorld, () #)
    forall {d}. State# d -> (# State# d, () #)
    loop
      where loop :: State# d -> (# State# d, () #)
    loop State# d
    s = case State# d -> (# State# d, Int#, ZonkAny 0 #)
    forall d a. State# d -> (# State# d, Int#, a #)
    getSpark# State# d
    s of
                       (# State# d
    s', Int#
    n, ZonkAny 0
    p #) ->
                          if Int# -> Bool
    isTrue# (Int#
    n Int# -> Int# -> Int#
    ==# Int#
    0#)
                          then (# State# d
    s', () #)
                          else ZonkAny 0
    p ZonkAny 0 -> (# State# d, () #) -> (# State# d, () #)
    forall a b. a -> b -> b
    `seq` State# d -> (# State# d, () #)
    loop State# d
    s'

    -- | List the Haskell threads of the current process.
    --
    -- @since base-4.18
    listThreads :: IO [ThreadId]
    listThreads :: IO [ThreadId]
    listThreads = (State# RealWorld -> (# State# RealWorld, [ThreadId] #))
    -> IO [ThreadId]
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, [ThreadId] #))
     -> IO [ThreadId])
    -> (State# RealWorld -> (# State# RealWorld, [ThreadId] #))
    -> IO [ThreadId]
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s ->
        case State# RealWorld -> (# State# RealWorld, Array# ThreadId# #)
    listThreads# State# RealWorld
    s of
          (# State# RealWorld
    s', Array# ThreadId#
    arr #) ->
            (# State# RealWorld
    s', (ThreadId# -> ThreadId) -> Array# ThreadId# -> [ThreadId]
    forall (a :: UnliftedType) b. (a -> b) -> Array# a -> [b]
    mapListArrayUnlifted ThreadId# -> ThreadId
    ThreadId Array# ThreadId#
    arr #)

    mapListArrayUnlifted :: forall (a :: TYPE UnliftedRep) b. (a -> b) -> Array# a -> [b]
    mapListArrayUnlifted :: forall (a :: UnliftedType) b. (a -> b) -> Array# a -> [b]
    mapListArrayUnlifted a -> b
    f Array# a
    arr = Int# -> [b]
    go Int#
    0#
      where
        sz :: Int#
    sz = Array# a -> Int#
    forall a. Array# a -> Int#
    sizeofArray# Array# a
    arr
        go :: Int# -> [b]
    go Int#
    i#
          | Int# -> Bool
    isTrue# (Int#
    i# Int# -> Int# -> Int#
    ==# Int#
    sz) = []
          | Bool
    otherwise = case Array# a -> Int# -> (# a #)
    forall a. Array# a -> Int# -> (# a #)
    indexArray# Array# a
    arr Int#
    i# of
                          (# a
    x #) -> a -> b
    f a
    x b -> [b] -> [b]
    forall a. a -> [a] -> [a]
    : Int# -> [b]
    go (Int#
    i# Int# -> Int# -> Int#
    +# Int#
    1#)
    {-# NOINLINE mapListArrayUnlifted #-}

    data BlockReason
      = BlockedOnMVar
            -- ^blocked on 'MVar'
      {- possibly (see 'threadstatus' below):
      | BlockedOnMVarRead
            -- ^blocked on reading an empty 'MVar'
      -}
      | BlockedOnBlackHole
            -- ^blocked on a computation in progress by another thread
      | BlockedOnException
            -- ^blocked in 'throwTo'
      | BlockedOnSTM
            -- ^blocked in 'retry' in an STM transaction
      | BlockedOnForeignCall
            -- ^currently in a foreign call
      | BlockedOnOther
            -- ^blocked on some other resource.  Without @-threaded@,
            -- I\/O and 'Control.Concurrent.threadDelay' show up as
            -- 'BlockedOnOther', with @-threaded@ they show up as 'BlockedOnMVar'.
      deriving ( BlockReason -> BlockReason -> Bool
    (BlockReason -> BlockReason -> Bool)
    -> (BlockReason -> BlockReason -> Bool) -> Eq BlockReason
    forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
    $c== :: BlockReason -> BlockReason -> Bool
    == :: BlockReason -> BlockReason -> Bool
    $c/= :: BlockReason -> BlockReason -> Bool
    /= :: BlockReason -> BlockReason -> Bool
    Eq   -- ^ @since base-4.3.0.0
               , Eq BlockReason
    Eq BlockReason =>
    (BlockReason -> BlockReason -> Ordering)
    -> (BlockReason -> BlockReason -> Bool)
    -> (BlockReason -> BlockReason -> Bool)
    -> (BlockReason -> BlockReason -> Bool)
    -> (BlockReason -> BlockReason -> Bool)
    -> (BlockReason -> BlockReason -> BlockReason)
    -> (BlockReason -> BlockReason -> BlockReason)
    -> Ord BlockReason
    BlockReason -> BlockReason -> Bool
    BlockReason -> BlockReason -> Ordering
    BlockReason -> BlockReason -> BlockReason
    forall a.
    Eq a =>
    (a -> a -> Ordering)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> a)
    -> (a -> a -> a)
    -> Ord a
    $ccompare :: BlockReason -> BlockReason -> Ordering
    compare :: BlockReason -> BlockReason -> Ordering
    $c< :: BlockReason -> BlockReason -> Bool
    < :: BlockReason -> BlockReason -> Bool
    $c<= :: BlockReason -> BlockReason -> Bool
    <= :: BlockReason -> BlockReason -> Bool
    $c> :: BlockReason -> BlockReason -> Bool
    > :: BlockReason -> BlockReason -> Bool
    $c>= :: BlockReason -> BlockReason -> Bool
    >= :: BlockReason -> BlockReason -> Bool
    $cmax :: BlockReason -> BlockReason -> BlockReason
    max :: BlockReason -> BlockReason -> BlockReason
    $cmin :: BlockReason -> BlockReason -> BlockReason
    min :: BlockReason -> BlockReason -> BlockReason
    Ord  -- ^ @since base-4.3.0.0
               , Int -> BlockReason -> ShowS
    [BlockReason] -> ShowS
    BlockReason -> String
    (Int -> BlockReason -> ShowS)
    -> (BlockReason -> String)
    -> ([BlockReason] -> ShowS)
    -> Show BlockReason
    forall a.
    (Int -> a -> ShowS) -> (a -> String) -> ([a] -> ShowS) -> Show a
    $cshowsPrec :: Int -> BlockReason -> ShowS
    showsPrec :: Int -> BlockReason -> ShowS
    $cshow :: BlockReason -> String
    show :: BlockReason -> String
    $cshowList :: [BlockReason] -> ShowS
    showList :: [BlockReason] -> ShowS
    Show -- ^ @since base-4.3.0.0
               )

    -- | The current status of a thread
    data ThreadStatus
      = ThreadRunning
            -- ^the thread is currently runnable or running
      | ThreadFinished
            -- ^the thread has finished
      | ThreadBlocked  BlockReason
            -- ^the thread is blocked on some resource
      | ThreadDied
            -- ^the thread received an uncaught exception
      deriving ( ThreadStatus -> ThreadStatus -> Bool
    (ThreadStatus -> ThreadStatus -> Bool)
    -> (ThreadStatus -> ThreadStatus -> Bool) -> Eq ThreadStatus
    forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
    $c== :: ThreadStatus -> ThreadStatus -> Bool
    == :: ThreadStatus -> ThreadStatus -> Bool
    $c/= :: ThreadStatus -> ThreadStatus -> Bool
    /= :: ThreadStatus -> ThreadStatus -> Bool
    Eq   -- ^ @since base-4.3.0.0
               , Eq ThreadStatus
    Eq ThreadStatus =>
    (ThreadStatus -> ThreadStatus -> Ordering)
    -> (ThreadStatus -> ThreadStatus -> Bool)
    -> (ThreadStatus -> ThreadStatus -> Bool)
    -> (ThreadStatus -> ThreadStatus -> Bool)
    -> (ThreadStatus -> ThreadStatus -> Bool)
    -> (ThreadStatus -> ThreadStatus -> ThreadStatus)
    -> (ThreadStatus -> ThreadStatus -> ThreadStatus)
    -> Ord ThreadStatus
    ThreadStatus -> ThreadStatus -> Bool
    ThreadStatus -> ThreadStatus -> Ordering
    ThreadStatus -> ThreadStatus -> ThreadStatus
    forall a.
    Eq a =>
    (a -> a -> Ordering)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> a)
    -> (a -> a -> a)
    -> Ord a
    $ccompare :: ThreadStatus -> ThreadStatus -> Ordering
    compare :: ThreadStatus -> ThreadStatus -> Ordering
    $c< :: ThreadStatus -> ThreadStatus -> Bool
    < :: ThreadStatus -> ThreadStatus -> Bool
    $c<= :: ThreadStatus -> ThreadStatus -> Bool
    <= :: ThreadStatus -> ThreadStatus -> Bool
    $c> :: ThreadStatus -> ThreadStatus -> Bool
    > :: ThreadStatus -> ThreadStatus -> Bool
    $c>= :: ThreadStatus -> ThreadStatus -> Bool
    >= :: ThreadStatus -> ThreadStatus -> Bool
    $cmax :: ThreadStatus -> ThreadStatus -> ThreadStatus
    max :: ThreadStatus -> ThreadStatus -> ThreadStatus
    $cmin :: ThreadStatus -> ThreadStatus -> ThreadStatus
    min :: ThreadStatus -> ThreadStatus -> ThreadStatus
    Ord  -- ^ @since base-4.3.0.0
               , Int -> ThreadStatus -> ShowS
    [ThreadStatus] -> ShowS
    ThreadStatus -> String
    (Int -> ThreadStatus -> ShowS)
    -> (ThreadStatus -> String)
    -> ([ThreadStatus] -> ShowS)
    -> Show ThreadStatus
    forall a.
    (Int -> a -> ShowS) -> (a -> String) -> ([a] -> ShowS) -> Show a
    $cshowsPrec :: Int -> ThreadStatus -> ShowS
    showsPrec :: Int -> ThreadStatus -> ShowS
    $cshow :: ThreadStatus -> String
    show :: ThreadStatus -> String
    $cshowList :: [ThreadStatus] -> ShowS
    showList :: [ThreadStatus] -> ShowS
    Show -- ^ @since base-4.3.0.0
               )

    -- | Query the current execution status of a thread.
    threadStatus :: ThreadId -> IO ThreadStatus
    threadStatus :: ThreadId -> IO ThreadStatus
    threadStatus (ThreadId ThreadId#
    t) = (State# RealWorld -> (# State# RealWorld, ThreadStatus #))
    -> IO ThreadStatus
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, ThreadStatus #))
     -> IO ThreadStatus)
    -> (State# RealWorld -> (# State# RealWorld, ThreadStatus #))
    -> IO ThreadStatus
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s ->
       case ThreadId#
    -> State# RealWorld -> (# State# RealWorld, Int#, Int#, Int# #)
    threadStatus# ThreadId#
    t State# RealWorld
    s of
        (# State# RealWorld
    s', Int#
    stat, Int#
    _cap, Int#
    _locked #) -> (# State# RealWorld
    s', Int -> ThreadStatus
    forall {a}. (Eq a, Num a) => a -> ThreadStatus
    mk_stat (Int# -> Int
    I# Int#
    stat) #)
       where
            -- NB. keep these in sync with rts/include/rts/Constants.h
         mk_stat :: a -> ThreadStatus
    mk_stat a
    0  = ThreadStatus
    ThreadRunning
         mk_stat a
    1  = BlockReason -> ThreadStatus
    ThreadBlocked BlockReason
    BlockedOnMVar
         mk_stat a
    2  = BlockReason -> ThreadStatus
    ThreadBlocked BlockReason
    BlockedOnBlackHole
         mk_stat a
    6  = BlockReason -> ThreadStatus
    ThreadBlocked BlockReason
    BlockedOnSTM
         mk_stat a
    10 = BlockReason -> ThreadStatus
    ThreadBlocked BlockReason
    BlockedOnForeignCall
         mk_stat a
    11 = BlockReason -> ThreadStatus
    ThreadBlocked BlockReason
    BlockedOnForeignCall
         mk_stat a
    12 = BlockReason -> ThreadStatus
    ThreadBlocked BlockReason
    BlockedOnException
         mk_stat a
    14 = BlockReason -> ThreadStatus
    ThreadBlocked BlockReason
    BlockedOnMVar -- possibly: BlockedOnMVarRead
         -- NB. these are hardcoded in rts/PrimOps.cmm
         mk_stat a
    16 = ThreadStatus
    ThreadFinished
         mk_stat a
    17 = ThreadStatus
    ThreadDied
         mk_stat a
    _  = BlockReason -> ThreadStatus
    ThreadBlocked BlockReason
    BlockedOnOther

    -- | Returns the number of the capability on which the thread is currently
    -- running, and a boolean indicating whether the thread is locked to
    -- that capability or not.  A thread is locked to a capability if it
    -- was created with @forkOn@.
    --
    -- @since base-4.4.0.0
    threadCapability :: ThreadId -> IO (Int, Bool)
    threadCapability :: ThreadId -> IO (Int, Bool)
    threadCapability (ThreadId ThreadId#
    t) = (State# RealWorld -> (# State# RealWorld, (Int, Bool) #))
    -> IO (Int, Bool)
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, (Int, Bool) #))
     -> IO (Int, Bool))
    -> (State# RealWorld -> (# State# RealWorld, (Int, Bool) #))
    -> IO (Int, Bool)
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s ->
       case ThreadId#
    -> State# RealWorld -> (# State# RealWorld, Int#, Int#, Int# #)
    threadStatus# ThreadId#
    t State# RealWorld
    s of
         (# State# RealWorld
    s', Int#
    _, Int#
    cap#, Int#
    locked# #) -> (# State# RealWorld
    s', (Int# -> Int
    I# Int#
    cap#, Int# -> Bool
    isTrue# (Int#
    locked# Int# -> Int# -> Int#
    /=# Int#
    0#)) #)

    -- | Query the label of thread, returning 'Nothing' if the
    -- thread's label has not been set.
    --
    -- @since base-4.18
    threadLabel :: ThreadId -> IO (Maybe String)
    threadLabel :: ThreadId -> IO (Maybe String)
    threadLabel (ThreadId ThreadId#
    t) = (State# RealWorld -> (# State# RealWorld, Maybe String #))
    -> IO (Maybe String)
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, Maybe String #))
     -> IO (Maybe String))
    -> (State# RealWorld -> (# State# RealWorld, Maybe String #))
    -> IO (Maybe String)
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s ->
        case ThreadId#
    -> State# RealWorld -> (# State# RealWorld, Int#, ByteArray# #)
    threadLabel# ThreadId#
    t State# RealWorld
    s of
          (# State# RealWorld
    s', Int#
    1#, ByteArray#
    lbl #) ->
              let lbl' :: String
    lbl' = ByteArray# -> String
    utf8DecodeByteArray# ByteArray#
    lbl
              in (# State# RealWorld
    s', String -> Maybe String
    forall a. a -> Maybe a
    Just String
    lbl' #)
          (# State# RealWorld
    s', Int#
    0#, ByteArray#
    _ #) -> (# State# RealWorld
    s', Maybe String
    forall a. Maybe a
    Nothing #)
          (# State# RealWorld, Int#, ByteArray# #)
    _ -> String -> (# State# RealWorld, Maybe String #)
    forall a. HasCallStack => String -> a
    error String
    "threadLabel: impossible"

    -- | Make a weak pointer to a 'ThreadId'.  It can be important to do
    -- this if you want to hold a reference to a 'ThreadId' while still
    -- allowing the thread to receive the @BlockedIndefinitely@ family of
    -- exceptions (e.g. 'BlockedIndefinitelyOnMVar').  Holding a normal
    -- 'ThreadId' reference will prevent the delivery of
    -- @BlockedIndefinitely@ exceptions because the reference could be
    -- used as the target of 'throwTo' at any time, which would unblock
    -- the thread.
    --
    -- Holding a @Weak ThreadId@, on the other hand, will not prevent the
    -- thread from receiving @BlockedIndefinitely@ exceptions.  It is
    -- still possible to throw an exception to a @Weak ThreadId@, but the
    -- caller must use @deRefWeak@ first to determine whether the thread
    -- still exists.
    --
    -- @since base-4.6.0.0
    mkWeakThreadId :: ThreadId -> IO (Weak ThreadId)
    mkWeakThreadId :: ThreadId -> IO (Weak ThreadId)
    mkWeakThreadId t :: ThreadId
    t@(ThreadId ThreadId#
    t#) = (State# RealWorld -> (# State# RealWorld, Weak ThreadId #))
    -> IO (Weak ThreadId)
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, Weak ThreadId #))
     -> IO (Weak ThreadId))
    -> (State# RealWorld -> (# State# RealWorld, Weak ThreadId #))
    -> IO (Weak ThreadId)
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s ->
       case ThreadId#
    -> ThreadId
    -> State# RealWorld
    -> (# State# RealWorld, Weak# ThreadId #)
    forall a b.
    a -> b -> State# RealWorld -> (# State# RealWorld, Weak# b #)
    mkWeakNoFinalizer# ThreadId#
    t# ThreadId
    t State# RealWorld
    s of
          (# State# RealWorld
    s1, Weak# ThreadId
    w #) -> (# State# RealWorld
    s1, Weak# ThreadId -> Weak ThreadId
    forall v. Weak# v -> Weak v
    Weak Weak# ThreadId
    w #)

    -----------------------------------------------------------------------------
    -- Transactional heap operations
    -----------------------------------------------------------------------------

    -- TVars are shared memory locations which support atomic memory
    -- transactions.

    -- |A monad supporting atomic memory transactions.
    newtype STM a = STM (State# RealWorld -> (# State# RealWorld, a #))

    unSTM :: STM a -> (State# RealWorld -> (# State# RealWorld, a #))
    unSTM :: forall a. STM a -> State# RealWorld -> (# State# RealWorld, a #)
    unSTM (STM State# RealWorld -> (# State# RealWorld, a #)
    a) = State# RealWorld -> (# State# RealWorld, a #)
    a

    -- | @since base-4.3.0.0
    instance  Functor STM where
       fmap :: forall a b. (a -> b) -> STM a -> STM b
    fmap a -> b
    f STM a
    x = STM a
    x STM a -> (a -> STM b) -> STM b
    forall a b. STM a -> (a -> STM b) -> STM b
    forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
    >>= (b -> STM b
    forall a. a -> STM a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure (b -> STM b) -> (a -> b) -> a -> STM b
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . a -> b
    f)

    -- | @since base-4.8.0.0
    instance Applicative STM where
      {-# INLINE pure #-}
      {-# INLINE (*>) #-}
      {-# INLINE liftA2 #-}
      pure :: forall a. a -> STM a
    pure a
    x = a -> STM a
    forall a. a -> STM a
    returnSTM a
    x
      <*> :: forall a b. STM (a -> b) -> STM a -> STM b
    (<*>) = STM (a -> b) -> STM a -> STM b
    forall (m :: * -> *) a b. Monad m => m (a -> b) -> m a -> m b
    ap
      liftA2 :: forall a b c. (a -> b -> c) -> STM a -> STM b -> STM c
    liftA2 = (a -> b -> c) -> STM a -> STM b -> STM c
    forall (m :: * -> *) a1 a2 r.
    Monad m =>
    (a1 -> a2 -> r) -> m a1 -> m a2 -> m r
    liftM2
      STM a
    m *> :: forall a b. STM a -> STM b -> STM b
    *> STM b
    k = STM a -> STM b -> STM b
    forall a b. STM a -> STM b -> STM b
    thenSTM STM a
    m STM b
    k

    -- | @since base-4.3.0.0
    instance  Monad STM  where
        {-# INLINE (>>=)  #-}
        STM a
    m >>= :: forall a b. STM a -> (a -> STM b) -> STM b
    >>= a -> STM b
    k     = STM a -> (a -> STM b) -> STM b
    forall a b. STM a -> (a -> STM b) -> STM b
    bindSTM STM a
    m a -> STM b
    k
        >> :: forall a b. STM a -> STM b -> STM b
    (>>) = STM a -> STM b -> STM b
    forall a b. STM a -> STM b -> STM b
    forall (f :: * -> *) a b. Applicative f => f a -> f b -> f b
    (*>)

    -- | @since base-4.17.0.0
    instance Semigroup a => Semigroup (STM a) where
        <> :: STM a -> STM a -> STM a
    (<>) = (a -> a -> a) -> STM a -> STM a -> STM a
    forall a b c. (a -> b -> c) -> STM a -> STM b -> STM c
    forall (f :: * -> *) a b c.
    Applicative f =>
    (a -> b -> c) -> f a -> f b -> f c
    liftA2 a -> a -> a
    forall a. Semigroup a => a -> a -> a
    (<>)

    -- | @since base-4.17.0.0
    instance Monoid a => Monoid (STM a) where
        mempty :: STM a
    mempty = a -> STM a
    forall a. a -> STM a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure a
    forall a. Monoid a => a
    mempty

    bindSTM :: STM a -> (a -> STM b) -> STM b
    bindSTM :: forall a b. STM a -> (a -> STM b) -> STM b
    bindSTM (STM State# RealWorld -> (# State# RealWorld, a #)
    m) a -> STM b
    k = (State# RealWorld -> (# State# RealWorld, b #)) -> STM b
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    STM ( \State# RealWorld
    s ->
      case State# RealWorld -> (# State# RealWorld, a #)
    m State# RealWorld
    s of
        (# State# RealWorld
    new_s, a
    a #) -> STM b -> State# RealWorld -> (# State# RealWorld, b #)
    forall a. STM a -> State# RealWorld -> (# State# RealWorld, a #)
    unSTM (a -> STM b
    k a
    a) State# RealWorld
    new_s
      )

    thenSTM :: STM a -> STM b -> STM b
    thenSTM :: forall a b. STM a -> STM b -> STM b
    thenSTM (STM State# RealWorld -> (# State# RealWorld, a #)
    m) STM b
    k = (State# RealWorld -> (# State# RealWorld, b #)) -> STM b
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    STM ( \State# RealWorld
    s ->
      case State# RealWorld -> (# State# RealWorld, a #)
    m State# RealWorld
    s of
        (# State# RealWorld
    new_s, a
    _ #) -> STM b -> State# RealWorld -> (# State# RealWorld, b #)
    forall a. STM a -> State# RealWorld -> (# State# RealWorld, a #)
    unSTM STM b
    k State# RealWorld
    new_s
      )

    returnSTM :: a -> STM a
    returnSTM :: forall a. a -> STM a
    returnSTM a
    x = (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    STM (\State# RealWorld
    s -> (# State# RealWorld
    s, a
    x #))

    -- | Takes the first non-'retry'ing 'STM' action.
    --
    -- @since base-4.8.0.0
    instance Alternative STM where
      empty :: forall a. STM a
    empty = STM a
    forall a. STM a
    retry
      <|> :: forall a. STM a -> STM a -> STM a
    (<|>) = STM a -> STM a -> STM a
    forall a. STM a -> STM a -> STM a
    orElse

    -- | Takes the first non-'retry'ing 'STM' action.
    --
    -- @since base-4.3.0.0
    instance MonadPlus STM

    -- | Unsafely performs IO in the STM monad.  Beware: this is a highly
    -- dangerous thing to do.
    --
    --   * The STM implementation will often run transactions multiple
    --     times, so you need to be prepared for this if your IO has any
    --     side effects.
    --
    --   * The STM implementation will abort transactions that are known to
    --     be invalid and need to be restarted.  This may happen in the middle
    --     of `unsafeIOToSTM`, so make sure you don't acquire any resources
    --     that need releasing (exception handlers are ignored when aborting
    --     the transaction).  That includes doing any IO using Handles, for
    --     example.  Getting this wrong will probably lead to random deadlocks.
    --
    --   * The transaction may have seen an inconsistent view of memory when
    --     the IO runs.  Invariants that you expect to be true throughout
    --     your program may not be true inside a transaction, due to the
    --     way transactions are implemented.  Normally this wouldn't be visible
    --     to the programmer, but using `unsafeIOToSTM` can expose it.
    --
    unsafeIOToSTM :: IO a -> STM a
    unsafeIOToSTM :: forall a. IO a -> STM a
    unsafeIOToSTM (IO State# RealWorld -> (# State# RealWorld, a #)
    m) = (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    STM State# RealWorld -> (# State# RealWorld, a #)
    m

    -- | Perform a series of STM actions atomically.
    --
    -- Using 'atomically' inside an 'unsafePerformIO' or 'unsafeInterleaveIO'
    -- subverts some of guarantees that STM provides. It makes it possible to
    -- run a transaction inside of another transaction, depending on when the
    -- thunk is evaluated. If a nested transaction is attempted, an exception
    -- is thrown by the runtime. It is possible to safely use 'atomically' inside
    -- 'unsafePerformIO' or 'unsafeInterleaveIO', but the typechecker does not
    -- rule out programs that may attempt nested transactions, meaning that
    -- the programmer must take special care to prevent these.
    --
    -- However, there are functions for creating transactional variables that
    -- can always be safely called in 'unsafePerformIO'. See: 'newTVarIO',
    -- 'Control.Concurrent.STM.TChan.newTChanIO',
    -- 'Control.Concurrent.STM.TChan.newBroadcastTChanIO',
    -- 'Control.Concurrent.STM.TQueue.newTQueueIO',
    -- 'Control.Concurrent.STM.TBQueue.newTBQueueIO', and
    -- 'Control.Concurrent.STM.TMVar.newTMVarIO'.
    --
    -- Using 'unsafePerformIO' inside of 'atomically' is also dangerous but for
    -- different reasons. See 'unsafeIOToSTM' for more on this.

    atomically :: STM a -> IO a
    atomically :: forall a. STM a -> IO a
    atomically (STM State# RealWorld -> (# State# RealWorld, a #)
    m) = (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO (\State# RealWorld
    s -> ((State# RealWorld -> (# State# RealWorld, a #))
    -> State# RealWorld -> (# State# RealWorld, a #)
    forall a.
    (State# RealWorld -> (# State# RealWorld, a #))
    -> State# RealWorld -> (# State# RealWorld, a #)
    atomically# State# RealWorld -> (# State# RealWorld, a #)
    m) State# RealWorld
    s )

    -- | Retry execution of the current memory transaction because it has seen
    -- values in 'TVar's which mean that it should not continue (e.g. the 'TVar's
    -- represent a shared buffer that is now empty).  The implementation may
    -- block the thread until one of the 'TVar's that it has read from has been
    -- updated. (GHC only)
    retry :: STM a
    retry :: forall a. STM a
    retry = (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    STM ((State# RealWorld -> (# State# RealWorld, a #)) -> STM a)
    -> (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s# -> State# RealWorld -> (# State# RealWorld, a #)
    forall a. State# RealWorld -> (# State# RealWorld, a #)
    retry# State# RealWorld
    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 :: forall a. STM a -> STM a -> STM a
    orElse (STM State# RealWorld -> (# State# RealWorld, a #)
    m) STM a
    e = (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    STM ((State# RealWorld -> (# State# RealWorld, a #)) -> STM a)
    -> (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s -> (State# RealWorld -> (# State# RealWorld, a #))
    -> (State# RealWorld -> (# State# RealWorld, a #))
    -> State# RealWorld
    -> (# State# RealWorld, a #)
    forall a.
    (State# RealWorld -> (# State# RealWorld, a #))
    -> (State# RealWorld -> (# State# RealWorld, a #))
    -> State# RealWorld
    -> (# State# RealWorld, a #)
    catchRetry# State# RealWorld -> (# State# RealWorld, a #)
    m (STM a -> State# RealWorld -> (# State# RealWorld, a #)
    forall a. STM a -> State# RealWorld -> (# State# RealWorld, a #)
    unSTM STM a
    e) State# RealWorld
    s

    -- | A variant of 'throw' that can only be used within the 'STM' monad.
    --
    -- Throwing an exception in @STM@ aborts the transaction and propagates the
    -- exception. If the exception is caught via 'catchSTM', only the changes
    -- enclosed by the catch are rolled back; changes made outside of 'catchSTM'
    -- persist.
    --
    -- If the exception is not caught inside of the 'STM', it is re-thrown by
    -- 'atomically', and the entire 'STM' is rolled back.
    --
    -- Although 'throwSTM' has a type that is an instance of the type of 'throw', the
    -- two functions are subtly different:
    --
    -- > throw e    `seq` x  ===> throw e
    -- > throwSTM e `seq` x  ===> x
    --
    -- The first example will cause the exception @e@ to be raised,
    -- whereas the second one won\'t.  In fact, 'throwSTM' will only cause
    -- an exception to be raised when it is used within the 'STM' monad.
    -- The 'throwSTM' variant should be used in preference to 'throw' to
    -- raise an exception within the 'STM' monad because it guarantees
    -- ordering with respect to other 'STM' operations, whereas 'throw'
    -- does not.
    throwSTM :: Exception e => e -> STM a
    throwSTM :: forall e a. Exception e => e -> STM a
    throwSTM e
    e = (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    STM ((State# RealWorld -> (# State# RealWorld, a #)) -> STM a)
    -> (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    forall a b. (a -> b) -> a -> b
    $ SomeException -> State# RealWorld -> (# State# RealWorld, a #)
    forall a b. a -> State# RealWorld -> (# State# RealWorld, b #)
    raiseIO# (e -> SomeException
    forall e. Exception e => e -> SomeException
    toException e
    e)

    -- | Exception handling within STM actions.
    --
    -- @'catchSTM' m f@ catches any exception thrown by @m@ using 'throwSTM',
    -- using the function @f@ to handle the exception. If an exception is
    -- thrown, any changes made by @m@ are rolled back, but changes prior to
    -- @m@ persist.
    catchSTM :: Exception e => STM a -> (e -> STM a) -> STM a
    catchSTM :: forall e a. Exception e => STM a -> (e -> STM a) -> STM a
    catchSTM (STM State# RealWorld -> (# State# RealWorld, a #)
    m) e -> STM a
    handler = (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    STM ((State# RealWorld -> (# State# RealWorld, a #)) -> STM a)
    -> (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    forall a b. (a -> b) -> a -> b
    $ (State# RealWorld -> (# State# RealWorld, a #))
    -> (SomeException -> State# RealWorld -> (# State# RealWorld, a #))
    -> State# RealWorld
    -> (# State# RealWorld, a #)
    forall a b.
    (State# RealWorld -> (# State# RealWorld, a #))
    -> (b -> State# RealWorld -> (# State# RealWorld, a #))
    -> State# RealWorld
    -> (# State# RealWorld, a #)
    catchSTM# State# RealWorld -> (# State# RealWorld, a #)
    m SomeException -> State# RealWorld -> (# State# RealWorld, a #)
    handler'
        where
          handler' :: SomeException -> State# RealWorld -> (# State# RealWorld, a #)
    handler' SomeException
    e = case SomeException -> Maybe e
    forall e. Exception e => SomeException -> Maybe e
    fromException SomeException
    e of
                         Just e
    e' -> STM a -> State# RealWorld -> (# State# RealWorld, a #)
    forall a. STM a -> State# RealWorld -> (# State# RealWorld, a #)
    unSTM (e -> STM a
    handler e
    e')
                         Maybe e
    Nothing -> SomeException -> State# RealWorld -> (# State# RealWorld, a #)
    forall a b. a -> State# RealWorld -> (# State# RealWorld, b #)
    raiseIO# SomeException
    e

    -- |Shared memory locations that support atomic memory transactions.
    data TVar a = TVar (TVar# RealWorld a)

    -- | @since base-4.8.0.0
    instance Eq (TVar a) where
            (TVar TVar# RealWorld a
    tvar1#) == :: TVar a -> TVar a -> Bool
    == (TVar TVar# RealWorld a
    tvar2#) = Int# -> Bool
    isTrue# (TVar# RealWorld a -> TVar# RealWorld a -> Int#
    forall s a. TVar# s a -> TVar# s a -> Int#
    sameTVar# TVar# RealWorld a
    tvar1# TVar# RealWorld a
    tvar2#)

    -- | Create a new 'TVar' holding a value supplied
    newTVar :: a -> STM (TVar a)
    newTVar :: forall a. a -> STM (TVar a)
    newTVar a
    val = (State# RealWorld -> (# State# RealWorld, TVar a #))
    -> STM (TVar a)
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    STM ((State# RealWorld -> (# State# RealWorld, TVar a #))
     -> STM (TVar a))
    -> (State# RealWorld -> (# State# RealWorld, TVar a #))
    -> STM (TVar a)
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s1# ->
        case a -> State# RealWorld -> (# State# RealWorld, TVar# RealWorld a #)
    forall a d. a -> State# d -> (# State# d, TVar# d a #)
    newTVar# a
    val State# RealWorld
    s1# of
             (# State# RealWorld
    s2#, TVar# RealWorld a
    tvar# #) -> (# State# RealWorld
    s2#, TVar# RealWorld a -> TVar a
    forall a. TVar# RealWorld a -> TVar a
    TVar TVar# RealWorld a
    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 :: forall a. a -> IO (TVar a)
    newTVarIO a
    val = (State# RealWorld -> (# State# RealWorld, TVar a #)) -> IO (TVar a)
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, TVar a #))
     -> IO (TVar a))
    -> (State# RealWorld -> (# State# RealWorld, TVar a #))
    -> IO (TVar a)
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s1# ->
        case a -> State# RealWorld -> (# State# RealWorld, TVar# RealWorld a #)
    forall a d. a -> State# d -> (# State# d, TVar# d a #)
    newTVar# a
    val State# RealWorld
    s1# of
             (# State# RealWorld
    s2#, TVar# RealWorld a
    tvar# #) -> (# State# RealWorld
    s2#, TVar# RealWorld a -> TVar a
    forall a. TVar# RealWorld a -> TVar a
    TVar TVar# RealWorld a
    tvar# #)

    -- | Return the current value stored in a 'TVar'.
    -- This is equivalent to
    --
    -- >  readTVarIO = atomically . readTVar
    --
    -- but works much faster, because it doesn't perform a complete
    -- transaction, it just reads the current value of the 'TVar'.
    readTVarIO :: TVar a -> IO a
    readTVarIO :: forall a. TVar a -> IO a
    readTVarIO (TVar TVar# RealWorld a
    tvar#) = (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    IO ((State# RealWorld -> (# State# RealWorld, a #)) -> IO a)
    -> (State# RealWorld -> (# State# RealWorld, a #)) -> IO a
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s# -> TVar# RealWorld a -> State# RealWorld -> (# State# RealWorld, a #)
    forall d a. TVar# d a -> State# d -> (# State# d, a #)
    readTVarIO# TVar# RealWorld a
    tvar# State# RealWorld
    s#

    -- |Return the current value stored in a 'TVar'.
    readTVar :: TVar a -> STM a
    readTVar :: forall a. TVar a -> STM a
    readTVar (TVar TVar# RealWorld a
    tvar#) = (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    STM ((State# RealWorld -> (# State# RealWorld, a #)) -> STM a)
    -> (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s# -> TVar# RealWorld a -> State# RealWorld -> (# State# RealWorld, a #)
    forall d a. TVar# d a -> State# d -> (# State# d, a #)
    readTVar# TVar# RealWorld a
    tvar# State# RealWorld
    s#

    -- |Write the supplied value into a 'TVar'.
    writeTVar :: TVar a -> a -> STM ()
    writeTVar :: forall a. TVar a -> a -> STM ()
    writeTVar (TVar TVar# RealWorld a
    tvar#) a
    val = (State# RealWorld -> (# State# RealWorld, () #)) -> STM ()
    forall a. (State# RealWorld -> (# State# RealWorld, a #)) -> STM a
    STM ((State# RealWorld -> (# State# RealWorld, () #)) -> STM ())
    -> (State# RealWorld -> (# State# RealWorld, () #)) -> STM ()
    forall a b. (a -> b) -> a -> b
    $ \State# RealWorld
    s1# ->
        case TVar# RealWorld a -> a -> State# RealWorld -> State# RealWorld
    forall d a. TVar# d a -> a -> State# d -> State# d
    writeTVar# TVar# RealWorld a
    tvar# a
    val State# RealWorld
    s1# of
             State# RealWorld
    s2# -> (# State# RealWorld
    s2#, () #)

    -----------------------------------------------------------------------------
    -- MVar utilities
    -----------------------------------------------------------------------------

    -- | Provide an 'IO' action with the current value of an 'MVar'. The 'MVar'
    -- will be empty for the duration that the action is running.
    withMVar :: MVar a -> (a -> IO b) -> IO b
    withMVar :: forall a b. MVar a -> (a -> IO b) -> IO b
    withMVar MVar a
    m a -> IO b
    io =
      ((forall a. IO a -> IO a) -> IO b) -> IO b
    forall b. ((forall a. IO a -> IO a) -> IO b) -> IO b
    mask (((forall a. IO a -> IO a) -> IO b) -> IO b)
    -> ((forall a. IO a -> IO a) -> IO b) -> IO b
    forall a b. (a -> b) -> a -> b
    $ \forall a. IO a -> IO a
    restore -> do
        a <- MVar a -> IO a
    forall a. MVar a -> IO a
    takeMVar MVar a
    m
        b <- catchAny (restore (io a))
                (\e
    e -> do MVar a -> a -> IO ()
    forall a. MVar a -> a -> IO ()
    putMVar MVar a
    m a
    a; e -> IO b
    forall a e. (HasCallStack, Exception e) => e -> a
    throw e
    e)
        putMVar m a
        return b

    -- | Modify the value of an 'MVar'.
    modifyMVar_ :: MVar a -> (a -> IO a) -> IO ()
    modifyMVar_ :: forall a. MVar a -> (a -> IO a) -> IO ()
    modifyMVar_ MVar a
    m a -> IO a
    io =
      ((forall a. IO a -> IO a) -> IO ()) -> IO ()
    forall b. ((forall a. IO a -> IO a) -> IO b) -> IO b
    mask (((forall a. IO a -> IO a) -> IO ()) -> IO ())
    -> ((forall a. IO a -> IO a) -> IO ()) -> IO ()
    forall a b. (a -> b) -> a -> b
    $ \forall a. IO a -> IO a
    restore -> do
        a <- MVar a -> IO a
    forall a. MVar a -> IO a
    takeMVar MVar a
    m
        a' <- catchAny (restore (io a))
                (\e
    e -> do MVar a -> a -> IO ()
    forall a. MVar a -> a -> IO ()
    putMVar MVar a
    m a
    a; e -> IO a
    forall a e. (HasCallStack, Exception e) => e -> a
    throw e
    e)
        putMVar m a'
        return ()

    -----------------------------------------------------------------------------
    -- Thread waiting
    -----------------------------------------------------------------------------

    -- Machinery needed to ensure that we only have one copy of certain
    -- CAFs in this module even when the base package is present twice, as
    -- it is when base is dynamically loaded into GHCi.  The RTS keeps
    -- track of the single true value of the CAF, so even when the CAFs in
    -- the dynamically-loaded base package are reverted, nothing bad
    -- happens.
    --
    sharedCAF :: a -> (Ptr a -> IO (Ptr a)) -> IO a
    sharedCAF :: forall a. a -> (Ptr a -> IO (Ptr a)) -> IO a
    sharedCAF a
    a Ptr a -> IO (Ptr a)
    get_or_set =
       IO a -> IO a
    forall a. IO a -> IO a
    mask_ (IO a -> IO a) -> IO a -> IO a
    forall a b. (a -> b) -> a -> b
    $ do
         stable_ref <- a -> IO (StablePtr a)
    forall a. a -> IO (StablePtr a)
    newStablePtr a
    a
         let ref = Ptr () -> Ptr b
    forall a b. Ptr a -> Ptr b
    castPtr (StablePtr a -> Ptr ()
    forall a. StablePtr a -> Ptr ()
    castStablePtrToPtr StablePtr a
    stable_ref)
         ref2 <- get_or_set ref
         if ref==ref2
            then return a
            else do freeStablePtr stable_ref
                    deRefStablePtr (castPtrToStablePtr (castPtr ref2))

    reportStackOverflow :: IO ()
    reportStackOverflow :: IO ()
    reportStackOverflow = do
         ThreadId tid <- IO ThreadId
    myThreadId
         c_reportStackOverflow tid

    reportError :: SomeException -> IO ()
    reportError :: SomeException -> IO ()
    reportError SomeException
    ex = do
       handler <- IO (SomeException -> IO ())
    getUncaughtExceptionHandler
       handler ex

    -- SUP: Are the hooks allowed to re-enter Haskell land?  If so, remove
    -- the unsafe below.
    foreign import ccall unsafe "reportStackOverflow"
            c_reportStackOverflow :: ThreadId# -> IO ()

    foreign import ccall unsafe "reportHeapOverflow"
            reportHeapOverflow :: IO ()

    {-# NOINLINE uncaughtExceptionHandler #-}
    uncaughtExceptionHandler :: IORef (SomeException -> IO ())
    uncaughtExceptionHandler :: IORef (SomeException -> IO ())
    uncaughtExceptionHandler = IO (IORef (SomeException -> IO ()))
    -> IORef (SomeException -> IO ())
    forall a. IO a -> a
    unsafePerformIO ((SomeException -> IO ()) -> IO (IORef (SomeException -> IO ()))
    forall a. a -> IO (IORef a)
    newIORef SomeException -> IO ()
    defaultHandler)
       where
          defaultHandler :: SomeException -> IO ()
          defaultHandler :: SomeException -> IO ()
    defaultHandler SomeException
    se = do
             (Handle -> IO ()
    hFlush Handle
    stdout) IO ()
    -> (forall e. (HasExceptionContext, Exception e) => e -> IO ())
    -> IO ()
    forall a.
    IO a
    -> (forall e. (HasExceptionContext, Exception e) => e -> IO a)
    -> IO a
    `catchAny` (\ e
    _ -> () -> IO ()
    forall a. a -> IO a
    forall (m :: * -> *) a. Monad m => a -> m a
    return ())

             let exMsg :: String
    exMsg = SomeException -> String
    displayExceptionWithInfo SomeException
    se
                 msg :: String
    msg = String
    "Uncaught exception " String -> ShowS
    forall a. [a] -> [a] -> [a]
    ++ String
    exMsg
             String -> (CString -> IO ()) -> IO ()
    forall a. String -> (CString -> IO a) -> IO a
    withCString String
    "%s" ((CString -> IO ()) -> IO ()) -> (CString -> IO ()) -> IO ()
    forall a b. (a -> b) -> a -> b
    $ \CString
    cfmt ->
              String -> (CString -> IO ()) -> IO ()
    forall a. String -> (CString -> IO a) -> IO a
    withCString String
    msg ((CString -> IO ()) -> IO ()) -> (CString -> IO ()) -> IO ()
    forall a b. (a -> b) -> a -> b
    $ \CString
    cmsg ->
                CString -> CString -> IO ()
    errorBelch CString
    cfmt CString
    cmsg

    -- don't use errorBelch() directly, because we cannot call varargs functions
    -- using the FFI.
    foreign import ccall unsafe "HsBase.h errorBelch2"
       errorBelch :: CString -> CString -> IO ()

    setUncaughtExceptionHandler :: (SomeException -> IO ()) -> IO ()
    setUncaughtExceptionHandler :: (SomeException -> IO ()) -> IO ()
    setUncaughtExceptionHandler = IORef (SomeException -> IO ()) -> (SomeException -> IO ()) -> IO ()
    forall a. IORef a -> a -> IO ()
    writeIORef IORef (SomeException -> IO ())
    uncaughtExceptionHandler

    getUncaughtExceptionHandler :: IO (SomeException -> IO ())
    getUncaughtExceptionHandler :: IO (SomeException -> IO ())
    getUncaughtExceptionHandler = IORef (SomeException -> IO ()) -> IO (SomeException -> IO ())
    forall a. IORef a -> IO a
    readIORef IORef (SomeException -> IO ())
    uncaughtExceptionHandler