[GHC] #4262: GHC's runtime never terminates unused worker threads

[GHC]

#4262: GHC's runtime never terminates unused worker threads
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    Reporter:  Remi                                      |        Owner:                         
        Type:  bug                                       |       Status:  new                    
    Priority:  normal                                    |    Milestone:  7.0.1                  
   Component:  Runtime System                            |      Version:  6.12.3                 
    Keywords:  worker thread foreign function interface  |     Testcase:                         
   Blockedby:                                            |   Difficulty:                         
          Os:  Unknown/Multiple                          |     Blocking:                         
Architecture:  Unknown/Multiple                          |      Failure:  Runtime performance bug
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Comment(by ezyang):

 Here is a somewhat refined test-case, though POSIX only.

 {{{
 {-# LANGUAGE ForeignFunctionInterface #-}
 module Main where

 import Control.Concurrent
 import Control.Monad
 import Foreign.C.Types
 import System.Mem
 import System.Posix.Process
 import System.Directory
 import Control.Concurrent.QSem

 foreign import ccall safe sleep :: CUInt -> IO ()

 main = do
     let amount = 200
     qsem <- newQSem 0
     replicateM_ amount . forkIO $ (sleep 2 >> signalQSem qsem)
     replicateM_ amount $ waitQSem qsem
     -- POSIX only: check thread usage manually
     pid <- getProcessID
     let dir = "/proc/" ++ show pid ++ "/task"
     contents <- getDirectoryContents dir
     let status = length contents - 2 -- . and ..
     print status
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4262#comment:3>
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