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haskellconcurrencyprocessghc

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

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 executeFile with -threaded runtime (see also this thread), no matter if I use +RTS -N or not. So I'd like to add a check to be sure that the daemon ins't compiled with -threaded. Is there a portable way to detect it?

Solution

  • There is the rtsSupportsBoundThreads value value in Control.Concurrent for this. For example:

    module Main (main) where

import Control.Concurrent

main :: IO ()
main = print rtsSupportsBoundThreads

    And during test:

    $ ghc -fforce-recomp Test.hs; ./Test
[1 of 1] Compiling Main             ( Test.hs, Test.o )
Linking Test ...
False
$ ghc -fforce-recomp -threaded Test.hs; ./Test
[1 of 1] Compiling Main             ( Test.hs, Test.o )
Linking Test ...
True

    Here is its C-part source code:

    HsBool
rtsSupportsBoundThreads(void)
{
#if defined(THREADED_RTS)
  return HS_BOOL_TRUE;
#else
  return HS_BOOL_FALSE;
#endif
}