STM experiment

[Luca Ciciriello]

Thanks Dan.
I understand, your explanation  is clear.
I just need to study more Haskell. Im' just a beginner but very  
enthusiastic learning this "think-different" language (I'm a 12-year  
experienced C++ programmer).

Thanks again.

Luca.


On Oct 2, 2009, at 6:28 PM, Daniel Peebles wrote:

> Hi Luca,
>
> Just in case you weren't aware of it, your example didn't actually
> contain any STM (beyond the import), just regular Haskell IO-based
> concurrency.
>
> But the answer to your question is that there's no synchronization on
> writing to a file descriptor, so both threads are "simultaneously"
> writing to stdout (hPutStr stdout "...\n" === putStrLn "..." by the
> way) and result in the interleaved results you see. One solution is to
> have a thread that effectively owns stdout, and instead of writing to
> stdout, you write to a Chan (Control.Concurrent.Chan) to talk to the
> stdout owner, who will then write out your messages. This approach
> will give you the "Hello world" or "world Hello" output that you were
> after.
>
> Hope this helps,
> Dan
>
> On Fri, Oct 2, 2009 at 12:16 PM, Luca Ciciriello
> <luca_ciciriello at hotmail.com> wrote:
>> Hi All.
>> I'm very new using Concurrency and STM in Haskell. I'm trying some  
>> basic
>> example using STM like this one:
>>
>> module Main
>>        where
>>
>> import IO
>> import Control.Concurrent
>> import Control.Concurrent.STM
>>
>> main :: IO ()
>> main = do
>>                 forkIO (hPutStr stdout "Hello")
>>                 hPutStr stdout " world\n"
>>
>>
>> Loading this module in GHCi and running main, the result is:
>>
>> wHoerllldo
>>
>> On MacOs X 10.5.8 and on WindowsXp
>>
>> Compiling this module with:
>>
>> ghc --make Main.hs -o Main
>>
>> and launcing ./Main the result is just:
>>
>> Terminal> world
>>
>> Am I doing something wrong? My expected result was Hello world (or  
>> world
>> Hello)
>>
>> Thanks in advance for any answer.
>>
>> Luca.
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>