[Haskell-beginners] Thread Blocking

[Eugene Perederey]

Well, not 50/50 but not deterministically -- I've caught
"fun1-main1-fun2" sequence,
"main1-fun1-main2" is much more often.
Since you are using -threaded, the Haskell threads are running on top
of the OS threads, so I guess it depends on the OS scheduler.

On 4 September 2012 12:27, Eugene Perederey <eugene.perederey at gmail.com> wrote:
> I added a few prints to your code
>
> fun m = do
>   putStrLn "fun1"
>   putMVar m 10
>   putStrLn "fun2"
>
>
> main = do
>   m <- newEmptyMVar
>   forkIO $ fun m
>   putStrLn "main1"
>   putMVar m 10
>   putStrLn "main2"
>
> It works 50/50 for me in Mac OS X 10.6.8.
>
> On 4 September 2012 12:16, mukesh tiwari <mukeshtiwari.iiitm at gmail.com> wrote:
>> Hi Eugene
>> Thank you for reply.
>>
>> On Wed, Sep 5, 2012 at 12:32 AM, Eugene Perederey
>> <eugene.perederey at gmail.com> wrote:
>>>
>>> Why do you think main should block more than once?
>>> I see only two possible scenarios: the fun thread puts to mvar first
>>> thus blocking main,
>>
>>
>> So at least in this case I should get thread blocked indefinitely in an MVar
>> operation
>>
>>>
>>> or 10 is put into mvar in main, blocking the other thread indefinitely.
>>
>>
>> or main will execute and fun thread will die. There are 50 - 50 chance for
>> this ( assuming both are equally likely ). I did some modification in my
>> code and Now I am  consistently getting "Concurrent: thread blocked
>> indefinitely in an MVar operation"
>>
>>
>> import Data.List
>> import Control.Concurrent
>>
>> fun m = do
>>    putMVar m 10
>>    return ()
>>
>>
>> main = do
>>   m <- newEmptyMVar
>>   forkIO $ fun m
>>   putStrLn "I am inside main"
>>
>>   putMVar m 10
>>   return ()
>>
>> [mukesh.tiwari@ Programming]$ ghc-7.4.1 -threaded -fforce-recomp
>> Concurrent.hs
>> [1 of 1] Compiling Main             ( Concurrent.hs, Concurrent.o )
>> Linking Concurrent ...
>> [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>> I am inside main
>> Concurrent: thread blocked indefinitely in an MVar operation
>>
>> [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>> I am inside main
>> Concurrent: thread blocked indefinitely in an MVar operation
>>
>> [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>> I am inside main
>> Concurrent: thread blocked indefinitely in an MVar operation
>>
>> [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>> I am inside main
>> Concurrent: thread blocked indefinitely in an MVar operation
>>
>> [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>> I am inside main
>> Concurrent: thread blocked indefinitely in an MVar operation
>>
>> My question is why the outcome in first case is deterministic. Every time
>> the code executing  ( at least half the time main thread should be blocked )
>> .
>>
>> Regards
>> Mukesh Tiwari
>>
>>>
>>>
>>> On 4 September 2012 11:54, mukesh tiwari <mukeshtiwari.iiitm at gmail.com>
>>> wrote:
>>> > Hello All
>>> > I was going trough Real World Haskell and it says "If we try to put a
>>> > value
>>> > into an MVar that is already full, our thread is put to sleep until
>>> > another
>>> > thread takes the value out". I wrote a simple code to block main
>>> >
>>> > import Data.List
>>> > import Control.Concurrent
>>> >
>>> > fun m = do
>>> >    putMVar m 10
>>> >    return ()
>>> >
>>> >
>>> > main = do
>>> >   m <- newEmptyMVar
>>> >   forkIO $ fun m
>>> >   putMVar m 10
>>> >   return ()
>>> >
>>> > What I am expecting that main should be blocked at least couple of times
>>> > but its behaving more deterministically.
>>> > [mukesh.tiwari@ Programming]$ ghc-7.4.1 -threaded -fforce-recomp
>>> > Concurrent.hs
>>> > [1 of 1] Compiling Main             ( Concurrent.hs, Concurrent.o )
>>> > Linking Concurrent ...
>>> > [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>>> > [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>>> > [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>>> > [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>>> > [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>>> > [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>>> > [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>>> > [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>>> > [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>>> > [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>>> > [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>>> > [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>>> > [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>>> > [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>>> > [mukesh.tiwari@ Programming]$ ./Concurrent  +RTS -N2
>>> > [mukesh.tiwari@ Programming]$
>>> >
>>> > I am expecting to get thread blocked indefinitely on MVar at least half
>>> > the
>>> > time. Could some one please tell me why this deterministic behavior ?
>>> > Regards
>>> > Mukesh Tiwari
>>> >
>>> >
>>> > _______________________________________________
>>> > Beginners mailing list
>>> > Beginners at haskell.org
>>> > http://www.haskell.org/mailman/listinfo/beginners
>>> >
>>>
>>>
>>>
>>> --
>>> Best,
>>> Eugene Perederey
>>
>>
>
>
>
> --
> Best,
> Eugene Perederey



-- 
Best,
Eugene Perederey