MVar, TVar, IORef, ...我无法加速一个 thunk 问题（我认为）。
（我原来的问题是一个线程代码，我做了“forkIO”n次调用“addMany”；但我认为我的问题是在“shW”函数上）
让下一个代码：
{-# LANGUAGE BangPatterns #-}
import Control.Concurrent
import Control.Monad
import System.Environment(getArgs)
import Data.Int
import Data.IORef
-- "i" times, add "n" for each IORef (in "a")
addMany :: [IORef Int64] -> Int64 -> Int64 -> IO ()
addMany !a !n !i =
forM_ [1..i] (\_ ->
forM_ a (shW n))
-- MVar, TVar, IORef, ... read/write (x' = x + k)
shR = readIORef
shW !k !r = atomicModifyIORef r (\ !x' -> (x' + k, ()))
main = do
(n':i':_) <- getArgs
let (n, i) = (read n', read i')
v <- forM [1..n] (\_ -> newIORef 0)
addMany v 1 i
mapM shR v >>= (putStrLn.show.sum)
然后，配置文件结果显示：
MUT time 3.12s ( 3.12s elapsed)
GC time 6.96s ( 6.96s elapsed)
...
COST CENTRE MODULE no. entries %time %alloc %time %alloc
MAIN MAIN 47 0 0.0 0.0 100.0 100.0
main Main 95 0 0.0 0.0 100.0 100.0
main.i Main 100 1 0.0 0.0 0.0 0.0
addMany Main 99 1 0.4 0.5 100.0 100.0
addMany.\ Main 101 15000 6.6 0.0 99.6 99.5
shW Main 102 2250000 92.7 99.5 93.0 99.5
shW.\ Main 104 2250000 0.3 0.0 0.3 0.0
我无法删除“shW”调用上的 thunk（并且内存使用量很大）。怎么了？
类似的 C# 代码运行得更快（很多）：
class Node {
private object m;
private int n;
public Node() {n = 0; m = new object();}
public void Inc() {lock(m) n++;}
public int Read() {return n;}
}
class MainClass {
public static void Main(string[] args) {
var nitems = 1000;
var nthreads = 6;
var niters = 100000;
var g = Enumerable.Range(0, nitems).Select(i => new Node()).ToArray();
Task.WaitAll(Enumerable.Range(0, nthreads).Select(q => Task.Factory.StartNew(() => {
var z = niters;
while(z-- > 0)
foreach(var i in g)
i.Inc();
})).ToArray());
Console.WriteLine("Sum node values: {0}", g.Sum(i => i.Read()));
}
}
非常感谢！
更新
解决了原始问题：https ://gist.github.com/3742897
非常感谢唐斯图尔特！
