[Haskell-cafe] Problems with Network/MVar

Pierre-Étienne Meunier pierreetienne.meunier at gmail.com
Tue Apr 1 11:35:20 UTC 2014

Em 01/04/2014, à(s) 11:29, Gregory Collins <greg at gregorycollins.net> escreveu:

> On Tue, Apr 1, 2014 at 11:21 AM, Pierre-Étienne Meunier <pierreetienne.meunier at gmail.com> wrote:
>> Hello cafe,
>> I’m trying to run a server to synchronize a bunch of machines, and one of the threads keeps crashing every ~50 hours.
> You seem to be throwing away the exception messages so it will be difficult to diagnose why.

You’re right, that was really stupid.
It is my first time dealing with (exceptions+threads+network) in Haskell.

>> server::Config -> MVar State -> IO ()
>> server config state=withSocketsDo $ do
>>  installHandler sigPIPE Ignore Nothing
>>  threads<-Sem.new $ maxThreads config
>>  forever $ do
>>        E.catch (bracket (listenOn $ port config)) sClose $
>>               \sock->forever $ do
>>                     (s,a,_)<-accept sock
> There is a race condition here, you can get an asynchronous exception any time after accepting the socket that would cause it to leak open. I'm guessing you might running out of file descriptors. This whole section should be run under "mask" and you should only unmask async exceptions when you know you've installed a signal handler to clean up afterwards.

Is this the same as using “bracket accept hClose $ blabla” (modulo correct types)?

>>                     wait threads
>>                     forkIO $ (reply state s a)`finally`(signal threads)`E.catch`(\e->let _=e::IOException in return ())
> Try "forkIOWithUnmask", same advice applies in the child thread.

Thanks. Let’s see how it goes in two days.


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