hello, i'm a bit lost here so i hope s.o. can help me here: seems i have a problem in my code when compiled with ghc-7.0.2: what i try to do: serverside: -listen on a socket and reply to requests client-side: -send a request to that server -wait for a response (with a timeout) any ideas on how i can make this work again without using the -threaded flag? is there is a better way for what i'm trying to achieve? many thanks, oliver the simplified code is available at https://gist.github.com/882770 explanation: the code forks of a lightweight thread (not an OS thread) that will listen for incoming responses. the main thread will go on to push out a message and then wait for the receiver thread to finish. i used to compile my application with the -threaded option but ran into some obscure FFI problems after upgrading from ghc-6.12.3 to ghc-7.0.2. so i tried to remove the -threaded option. but now the message does not get pushed out until the receiver-thread has finished. what is strange to me is that this worked without problems on 6.12.3 but not on 7.0.2. also the behavior is a little different on mac os X with 7.0.2: here i get a "resource vanished (Connection reset by peer)" see the output of the program below ([S] marks output from the main thread, [R] from the receiver thread) compiled on ghc-7.0.2/ubuntu 64bit, without -threaded "running all things..." [R]listening for response... [R]wait for data with timeout:2000 ms ......................................................................................................................................................................................................... [R]no message available [S]pushing out the message [S]sending --> "\EOT\ETX" "[S]going on..." Nothing compiled on ghc-7.0.2/ubuntu 64bit, using -threaded "running all things..." [S]pushing out the message [R]listening for response... [S]sending --> "\EOT\ETX" [R]wait for data with timeout:2000 ms "[S]going on..." ..................................................Just "\ETX\EOT" and...also very strange: when i introduce a putStrLn in the main thread (not a print !) it will work again...only a lot (see code snipped line38: putStrLn "[S]hickup" "running all things..." [S]hickup [R]listening for response... [S]pushing out the message [S]sending --> "\EOT\ETX" [R]wait for data with timeout:2000 ms "[S]going on..." ..................................................Just "\ETX\EOT"