shakeThreads=0 doesn't seem to work on OSX

[afranchuk]

Specifically on Mac OSX Mojave, setting shakeThreads to 0 runs with 1 thread on a system with 8 cores (16 HT).

[ndmitchell]

Did you compile your Haskell program with -threaded or not?

Here's the code that computes the number of threads if you pick 0. Can you suggest how to adjust it?

shake/src/General/Extra.hs

Lines 113 to 126 in a85aa20

	getProcessorCount :: IO Int
	-- unsafePefromIO so we cache the result and only compute it once
	getProcessorCount = let res = unsafePerformIO act in return res
	where
	act =
	if rtsSupportsBoundThreads then
	fromIntegral <$> getNumProcessors
	else do
	env <- lookupEnv "NUMBER_OF_PROCESSORS"
	case env of
	Just s | [(i,"")] <- reads s -> return i
	_ -> do
	src <- readFile' "/proc/cpuinfo" `catchIO` \_ -> return ""
	return $! max 1 $ length [() | x <- lines src, "processor" `isPrefixOf` x]

[afranchuk]

Unfortunately I don't have a mac myself. My program is built the same (using stack) on windows, mac, and linux, and someone using it on mac said it was only using one core (and I saw the behavior to verify). Manually specifying -jn (where n > 0) worked as expected, so I think that indicates stack is including -threaded when building.

I will try to get onto a mac system to see what these values are. It's possible that getNumProcessors is where the issue lies...

[ndmitchell]

It definitely works on some Mac's, and I test that in the CI, so it's not as simple as "a Mac". I have no idea what else might be a relevant variable though.

[afranchuk]

Yeah I believe that. I'll try to get an equivalent system to test on, or maybe ask my coworker to try it out for me.