How to detect if a program has been compiled using -threaded?

Question

I\'m working on a Haskell daemon that uses POSIX fork/exec together with file locking mechanism. My experiments show that file locks aren\'t inherited during executeFi

Answer 1

This is a dirty hack and might be not portable but I can confirm it works for ghc-7.6.3 on linux:

isThreaded :: IO (Maybe Bool)
isThreaded = do
  tid  <- forkIO $ threadDelay 1000000
  yield
  stat <- threadStatus tid
  killThread tid
  case stat of
    ThreadBlocked BlockedOnMVar  -> return (Just True)
    ThreadBlocked BlockedOnOther -> return (Just False)
    _                            -> return Nothing

See BlockedOnOther docstring for details.