errno is Haskell thread local

gistfile1.hs

{-# LANGUAGE ForeignFunctionInterface #-}

import Control.Concurrent
import Foreign.C.Types
import Foreign.C.Error

main :: IO ()
main = do
    s <- c_socket 2 1 0
    forkIO $ do
        c_close s
        putStrLn "a closed"
        threadDelay 200000
        Errno e <- getErrno
        putStrLn $ "a " ++ show e
    forkIO $ do
        threadDelay 100000
        c_close s
        putStrLn "b closed"
        Errno e <- getErrno
        putStrLn $ "b " ++ show e
    threadDelay 1000000

foreign import ccall unsafe "socket"
    c_socket :: CInt -> CInt -> CInt -> IO CInt

foreign import ccall unsafe "close"
    c_close :: CInt -> IO CInt