blocking parallel program

[Facundo Domínguez]

Thanks. I just tried that. Unfortunately, it doesn't seem to help.

Facundo

On Sat, Oct 19, 2013 at 8:47 PM, Edward Z. Yang <ezyang at mit.edu> wrote:
> Hello Facundo,
>
> The reason is that you have compiled the program to be multithreaded, but it
> is not running with multiple cores. Compile also with -rtsopts and then
> pass +RTS -N2 to the program.
>
> Excerpts from Facundo Domínguez's message of Sat Oct 19 15:19:22 -0700 2013:
>> Hello,
>>    Below is a program that seems to block indefinitely with ghc in a
>> multicore machine. This program has a loop that does not produce
>> allocations, and I understand that this may grab one of the cores. The
>> question is, why can't the other cores take the blocked thread?
>>
>> The program was compiled with:
>>
>> $ ghc --make -O -threaded test.hs
>>
>> and it is run with:
>>
>> $ ./test
>>
>> Program text follows.
>>
>> Thanks,
>> Facundo
>>
>> --------
>>
>> import Control.Concurrent
>> import Control.Monad
>> import System.Environment
>>
>> main :: IO ()
>> main = do
>>   y <- getArgs
>>   mv0 <- newEmptyMVar
>>   mv1 <- newEmptyMVar
>>   forkIO $ do
>>     takeMVar mv0
>>     putMVar mv1 ()
>>     loop (y == ["yield"])
>>   putMVar mv0 ()
>>   takeMVar mv1
>>
>> loop :: Bool -> IO ()
>> loop cooperative = go
>>   where
>>     go = when cooperative yield >> go