Dear all,
I've thought the following three (dummy) programs would run some of
their parts in parallel (on dual core) if compiled with option threaded
(smp). The truth is that only the first one exploits multicore CPU. Why?
Moreover, using RTS option -sstderr makes runtime not to evaluate in
parallel even for the first program. Why?
Thanks for tips
Dusan
My arch:
Linux pcx 2.6.24-ARCH #1 SMP PREEMPT Sun Feb 10 15:44:59 CET 2008 x86_64
Intel(R) Core(TM)2 CPU 6600 @ 2.40GHz GenuineIntel GNU/Linux
My ghc:
The Glorious Glasgow Haskell Compilation System, version 6.8.2
/64bit, binary distro for FC/
----------------------------------------------------
Prog 1:
module Main() where
import Control.Parallel
import Control.Parallel.Strategies
fibs :: Integer -> Integer
fibs n | n > 1 = fibs (n-1) + fibs (n-2)
| n == 1 = 1
| True = 0
fib n = if n<0 then error "Negative input to fib!"
else f1+f2
where
[f1,f2] = parMap rnf fibs [(n-1),(n-2)]
main = do
putStrLn "Starting..."
putStrLn $ "Fib 43: " ++ show (fib 43)
putStrLn "Done!"
----------------------------------------------------
Prog 2:
module Main() where
import Control.Concurrent
import Control.Concurrent.MVar
fibs :: Integer -> Integer
fibs n | n > 1 = fibs (n-1) + fibs (n-2)
| n == 1 = 1
| True = 0
fib n = if n<0 then error "Negative input to fib!"
else do
v1 <- newEmptyMVar
v2 <- newEmptyMVar
h1 <- forkIO $ putMVar v1 $ fibs (n-1)
h2 <- forkIO $ putMVar v2 $ fibs (n-2)
f1 <- takeMVar v1
f2 <- takeMVar v2
killThread h1
killThread h2
return (f1+f2)
main = do
putStrLn "Starting..."
f <- fib 43
putStrLn $ "Fib 43: " ++ show f
putStrLn "Done!"
----------------------------------------------------
Prog 3:
module Main() where
import Control.Concurrent
import Control.Concurrent.MVar
fibs :: Integer -> Integer
fibs n | n > 1 = fibs (n-1) + fibs (n-2)
| n == 1 = 1
| True = 0
fib n = if n<0 then error "Negative input to fib!"
else do
v1 <- newEmptyMVar
v2 <- newEmptyMVar
h1 <- forkOS $ putMVar v1 $ fibs (n-1)
h2 <- forkOS $ putMVar v2 $ fibs (n-2)
f1 <- takeMVar v1
f2 <- takeMVar v2
killThread h1
killThread h2
return (f1+f2)
main = do
putStrLn "Starting..."
f <- fib 43
putStrLn $ "Fib 43: " ++ show f
putStrLn "Done!"
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