, forkOnIO -- :: Int -> IO a -> IO ThreadId
, forkOnIOUnmasked
, numCapabilities -- :: Int
+ , getNumCapabilities -- :: IO Int
, numSparks -- :: IO Int
, childHandler -- :: Exception -> IO ()
, myThreadId -- :: IO ThreadId
know in advance how best to distribute the threads.
The `Int` argument specifies the CPU number; it is interpreted modulo
-'numCapabilities' (note that it actually specifies a capability number
-rather than a CPU number, but to a first approximation the two are
-equivalent).
+the value returned by 'getNumCapabilities'.
-}
forkOnIO :: Int -> IO () -> IO ThreadId
forkOnIO (I# cpu) action = IO $ \ s ->
-- Haskell threads that can run truly simultaneously at any given
-- time, and is typically set to the number of physical CPU cores on
-- the machine.
+--
+-- Strictly speaking it is better to use 'getNumCapabilities', because
+-- the number of capabilities might vary at runtime.
+--
numCapabilities :: Int
-numCapabilities = unsafePerformIO $ do
- n <- peek n_capabilities
- return (fromIntegral n)
+numCapabilities = unsafePerformIO $ getNumCapabilities
+
+{- |
+Returns the number of Haskell threads that can run truly
+simultaneously (on separate physical processors) at any given time.
+The CPU number passed to `forkOnIO` is interpreted modulo this
+value.
+
+An implementation in which Haskell threads are mapped directly to
+OS threads might return the number of physical processor cores in
+the machine, and 'forkOnIO' would be implemented using the OS's
+affinity facilities. An implementation that schedules Haskell
+threads onto a smaller number of OS threads (like GHC) would return
+the number of such OS threads that can be running simultaneously.
+
+GHC notes: this returns the number passed as the argument to the
+@+RTS -N@ flag. In current implementations, the value is fixed
+when the program starts and never changes, but it is possible that
+in the future the number of capabilities might vary at runtime.
+-}
+getNumCapabilities :: IO Int
+getNumCapabilities = do
+ n <- peek n_capabilities
+ return (fromIntegral n)
-- | Returns the number of sparks currently in the local spark pool
numSparks :: IO Int
threadStatus :: ThreadId -> IO ThreadStatus
threadStatus (ThreadId t) = IO $ \s ->
case threadStatus# t s of
- (# s', stat #) -> (# s', mk_stat (I# stat) #)
+ (# s', stat, _cap #) -> (# s', mk_stat (I# stat) #)
where
-- NB. keep these in sync with includes/Constants.h
mk_stat 0 = ThreadRunning
mk_stat 1 = ThreadBlocked BlockedOnMVar
mk_stat 2 = ThreadBlocked BlockedOnBlackHole
- mk_stat 3 = ThreadBlocked BlockedOnException
- mk_stat 7 = ThreadBlocked BlockedOnSTM
+ mk_stat 6 = ThreadBlocked BlockedOnSTM
+ mk_stat 10 = ThreadBlocked BlockedOnForeignCall
mk_stat 11 = ThreadBlocked BlockedOnForeignCall
- mk_stat 12 = ThreadBlocked BlockedOnForeignCall
+ mk_stat 12 = ThreadBlocked BlockedOnException
mk_stat 16 = ThreadFinished
mk_stat 17 = ThreadDied
mk_stat _ = ThreadBlocked BlockedOnOther