[GHC] #8521: Tight loop prevents other threads from running in available cores

[GHC]

#8521: Tight loop prevents other threads from running in available cores
-------------------------------------+-------------------------------------
       Reporter:  facundo.dominguez  |             Owner:  simonmar
           Type:  bug                |            Status:  new
       Priority:  normal             |         Milestone:
      Component:  Runtime System     |           Version:  7.6.3
       Keywords:                     |  Operating System:  Unknown/Multiple
   Architecture:  x86_64 (amd64)     |   Type of failure:  None/Unknown
     Difficulty:  Unknown            |         Test Case:
     Blocked By:                     |          Blocking:
Related Tickets:                     |
-------------------------------------+-------------------------------------
 The following program does not terminate when compiled with:
 {{{ghc --make -O -threaded test.hs}}}
 and executed on linux on an amd64 machine with 16 cores with:
 {{{./test}}}

 {{{
 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
      >>= print

 loop :: Bool -> IO ()
 loop cooperative = go
   where
     go = when cooperative yield >> go
 }}}

 Here [1] is the discussion about it so far.

 [1] http://www.haskell.org/pipermail/glasgow-haskell-
 users/2013-October/024412.html

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8521>
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