Quoth Claude Heiland-Allen <claudiusmaxi...@goto10.org>,
...
> The conclusion I drew was that "unsafe" foreign functions block the
> current "capability" (OS thread) and any "threads" (Haskell forkIO etc)
> currently scheduled on that capability, but other capabilities and
> threads continue executing as normal.
If a trivial test program would help, here I call the sleep() function,
which I believe on a POSIX platform suspends the thread until receipt
of a SIGALRM.
If "unsafe", during the execution of sleep() in one thread, Haskell
execution will be blocked in the other, so they will alternate.
If "safe", the two sleep intervals will overlap. I believe we all
now expect that, but if it does come as a surprise, I hope someone
will test it on a more common platform. +RTS -N2 makes no difference.
Donn Cave, d...@avvanta.com
-----------------------------------
{-# LANGUAGE ForeignFunctionInterface #-}
module Main (main) where
import Control.Concurrent (forkOS)
import Foreign
import Foreign.C
foreign import ccall unsafe "sleep" sleep :: CInt -> IO CInt
rep :: (CInt -> IO CInt) -> CInt -> IO ()
rep f s = do
print s
f s
rep f s
main = do
forkOS $ rep sleep 3
rep sleep 1
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