[Haskell-cafe] interrupting an accept()ing thread

[Lukas Mai]

Am Freitag, 6. Juli 2007 02:13 schrieb Thomas Conway:

> Here's my solution:
>
> acceptLoop sok reqChan = do
>     req <- Network.Socket.accept sok
>     atomically (writeTChan reqChan req)
>     acceptLoop sok reqChan
>
> mainLoop reqChan quitVar liveOpCountVar = do
>     action <- atomically (quitNow `orElse` getReq)
>     case action of
>         Nothing -> return ()
>         Just (reqSok,reqAddr) -> do
>             atomically $ do
>                 liveOpCount <- readTVar liveOpCountVar
>                 writeTVar liveOpCountVar (liveOpCount + 1)
>             forkIO (doSession reqSok reqAddr quitVar liveOpCountVar)
>             mainLoop reqChan quitVar liveOpCountVar
>     where
>     quitNow = do
>         q <- readTVar quitVar
>         case q of
>             True -> return Nothing
>             False -> retry
>
>     getReq = do
>         req <- readTChan reqChan
>         return (Just req)
>
> doit sok = do
>     reqChan <- atomically newTChan
>     quitVar <- atomically (newTVar False)
>     liveOpCountVar <- atomically (newTVar 0)
>     forkIO (acceptLoop sok reqChan)
>     mainLoop reqChan quitVar liveOpCountVar
>     atomically $ do
>         liveOpCount <- readTVar liveOpCountVar
>         if liveOpCount > 0
>             then retry
>             else return ()
>
> Although doSession is not included, obviously when you want to quit,
> something in doSession should set quitVar to True. Also, as suggested
> elsewhere, doSession should involve a "finally" clauses to make sure
> the live op count gets decremented.

I don't see how this solves the problem. AFAICS acceptLoop never returns
and sok is never closed. On the other hand, my program doesn't need a
liveOpCount because the subthreads take care of themselves. It's just the
accept loop I need to break somehow.

Lukas