Hi all, I'm not able to find out how one can use Network.Curl with the threaded runtime safely. I have this simple example: import Network.Curl import Control.Concurrent import Control.Concurrent.MVar getUrl :: (Monad m) => String -> IO (m String) getUrl url = do (code, body) <- curlGetString url [CurlSSLVerifyPeer False, CurlSSLVerifyHost 0, CurlTimeout 15, CurlConnectTimeout 5] return $ case code of CurlOK -> return body _ -> fail $ "Curl error for " ++ url ++ " error " ++ show code runGet :: String -> MVar (Maybe String) -> IO () runGet url mv = do body <- getUrl url putMVar mv body main = withCurlDo $ do let urls = replicate 10 "https://google.com/" mvs <- mapM (\_ -> newEmptyMVar) urls mapM_ (\(mv, url) -> forkIO (runGet url mv)) $ zip mvs urls mapM (\mv -> takeMVar mv >>= print) mvs threadDelay 10000000 When using curl linked with GnuTLS and running it with the multi-threaded runtime, it fails immediately with: $ ./main main: ath.c:193: _gcry_ath_mutex_lock: Assertion `*lock == ((ath_mutex_t) 0)' failed. Aborted (core dumped) Reading the Network.Curl docs, it seems that using withCurlDo should be enough to make this work (although I'm not sure about the description of the function and "no forking or lazy returns"). Using Network.Curl built against the OpenSSL headers does successfully retrieve all URLs, but fails a bit later (during the threadDelay, probably in GC) again with segmentation fault in libcurl.4.so. I've tried changing forkIO to forkOS, but still no luck, with either SSL library. Any ideas what I'm doing wrong? regards, iustin