Re: [Haskell-cafe] Threads and hGetLine
There are two threads, one which is waits on input via
hGetLine
and another, which should terminate this thread or close this handle.
like this? The trick is to fork the blocking call (hGetLine)
and wait on an MVar. That way, the kill signal can be handled:
{-# language PatternSignatures #-}
import Control.Concurrent
import Control.Concurrent.MVar
import Control.Exception
import System.IO
main = do
pid - forkIO $ do
s - wawiter
putStrLn s
threadDelay $ 5 * 10^6
killThread pid
waiter = do
v - newEmptyMVar
forkIO $ do s - hGetLine stdin ; putMVar v s
readMVar v `Control.Exception.catch`
\ (e :: AsyncException ) - return killed
PS: and I refuse to use the ScopedTypeVariables pragma
since obviously there are no type variables.
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[Haskell-cafe] Threads and hGetLine
Hello, The simplified problem: There are two threads, one which is waits on input via hGetLine and another, which should terminate this thread or close this handle. hClose as well as killThread doesn't seem to work, caused by the fact, that the thread is blocked until input is availiable. Hopefully you have some solution how to kill the thread and/or close the handle and/or have some other idea to get the lined input in the other thread. -- Thanks in advance H. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Threads and hGetLine
Hi -- I am not well-versed in Haskell-specific multi-threading, but usually there is a better way to do what you want that does not involve killing threads (which in most cases is bad idea.) For example, using non-blocking IO and e.g. a synchronized condition variable; hWaitForInput might work in your case, or something like the following: http://hpaste.org/52742 Nevertheless, as a guess, I think you may want to try using closeFdWith, perhaps combined with a call to threadWaitRead before actually calling hGetLine. The wrinkle is that those operate on file descriptors instead of handles, but there are fdToHandle/mkHandleFromFD to bridge the gap. Hope that helps, Alvaro On Sat, Apr 28, 2012 at 2:23 PM, H. M. h._h._...@hotmail.com wrote: Hello, The simplified problem: There are two threads, one which is waits on input via hGetLine and another, which should terminate this thread or close this handle. hClose as well as killThread doesn't seem to work, caused by the fact, that the thread is blocked until input is availiable. Hopefully you have some solution how to kill the thread and/or close the handle and/or have some other idea to get the lined input in the other thread. -- Thanks in advance H. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Threads and hGetLine
On Sat, Apr 28, 2012 at 2:23 PM, H. M. h._h._...@hotmail.com wrote: There are two threads, one which is waits on input via hGetLine and another, which should terminate this thread or close this handle. hClose as well as killThread doesn't seem to work, caused by the fact, that the thread is blocked until input is availiable. What OS? GHC currently doesn't have proper IO manager support for Windows. On Windows, IO is performed through FFI calls. An FFI call masks asynchronous exceptions (C code generally doesn't expect to be interrupted at arbitrary points in time). If another thread tries to `killThread` the thread waiting for input, the exception will not be received until the FFI call completes. This means both threads will hang. -Joey ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
