running for long enough...

Andre W B Furtado [email protected]
Thu, 19 Apr 2001 02:00:17 -0300


About the program below, someone (I think Simon Marlow) said that if I run
it for long enough, I'll see "a"s rather than "b"s. I would like to know for
how long I will have to wait, since 2 hours were not enough to see it
switching from "b"s to "a"s.

> main = forkIO a >> b
>  where
>   a = putStrLn "a" >> a
>   b = putStrLn "b" >> b

Thanks,
Andre Furtado



----- Original Message -----
From: Tom Pledger <[email protected]>
To: <[email protected]>
Sent: Tuesday, April 17, 2001 12:24 AM
Subject: Concurrent Haskell (Ops...)


> Andre W B Furtado writes:
>  :
>  | import Concurrent
>  |
>  | main :: IO()
>  | main = let loop ch = putStr(ch) >> loop ch in
>  |        forkIO (loop "a") >> loop "z"
>  |
>  | But this program prints only 'z's, and no 'a's. I was surprised by
>  | this, since GHC uses preemptive multitasking, not cooperative
>  | multitasking. Does anyone knows what's going wrong?
>
> By my count, this is now a TAQ (thrice asked question).  :-)
>
>
http://www.mail-archive.com/[email protected]/msg01599.html
>
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