我是一个Haskell新手，对于这个程序的性能表现感到困惑。我尝试在不同的地方强制使用严格变量，但似乎没有什么区别。
下面是我的代码（这个程序的目的是从标准输入中产生输入字节的频率）：
{-# LANGUAGE BangPatterns #-}
import Control.Concurrent (forkIO, killThread)
import Control.Concurrent.MVar
import qualified Data.IntMap as IntMap
import Data.IntMap.Strict (IntMap)
import Control.Monad.Fix
import Control.Monad (when)
import qualified Data.Char as Char
import qualified System.IO as IO
import System.IO (hSetBinaryMode, hFlush)
import Data.List as List
import Text.PrettyPrint.Boxes as Boxes
import Text.Printf (printf)
import Data.Function
data BFreq = BFreq Integer (IntMap Integer)
main :: IO ()
main = do
putStrLn "analyze data from stdin"
hSetBinaryMode IO.stdin True
mv <- newEmptyMVar
tid <- forkIO $ statusUpdater mv
bf <- run mv
killThread tid
displayResults bf
resultTable :: [[String]] -> Box
resultTable rows =
Boxes.hsep 4 Boxes.left boxed_cols
where
cols = transpose rows
boxed_cols = map (Boxes.vcat Boxes.left . map text) cols
displayResults :: BFreq -> IO ()
displayResults (BFreq n counts) = do
putStrLn $ "read " ++ (show n) ++ " bytes"
when (n > 0) (displayFreqs n counts)
displayFreqs :: Integer -> IntMap Integer -> IO ()
displayFreqs n counts =
do
putStrLn "frequencies:"
Boxes.printBox $ resultTable rows
where
cmp x y = compare (snd y) (snd x)
sorted_counts = List.sortBy cmp $ IntMap.assocs counts
intdiv :: Integer -> Integer -> Float
intdiv a b = (fromIntegral a) / (fromIntegral b)
percent y = printf "%.2f" (100*intdiv y n)
show_byte x = (show $ Char.chr x) ++ " (" ++ (show x) ++ "):"
show_count y = (percent y) ++ "% (" ++ (show y) ++ ")"
rows = map (\(x,y) -> [show_byte x, show_count y]) sorted_counts
run :: MVar Integer -> IO BFreq
run mv =
fn mv 0 IntMap.empty
where
fn mv !n !mp =
do
tryPutMVar mv n
eof <- IO.isEOF
if eof
then return $ BFreq n mp
else do
b <- getChar
fn mv (1+n) (new_map b)
where
k x = Char.ord x
old_val x = IntMap.findWithDefault 0 (k x) mp
new_map x = IntMap.insert (k x) ((old_val x)+1) mp
statusUpdater :: MVar Integer -> IO ()
statusUpdater mv =
do
takeMVar mv >>= print_progress
statusUpdater mv
where
print_progress n =
do
putStr $ "\rbytes: "
when (gbs > 0) $ putStr $ (show gbs) ++ " GBs "
when (mbs > 0) $ putStr $ (show mbs) ++ " MBs "
when (kbs > 0) $ putStr $ (show kbs) ++ " KBs "
when (gbs < 1 && mbs < 1 && kbs < 1) $ putStr $ (show bs) ++ " Bs "
hFlush IO.stdout
where
(gbs, gbr) = quotRem n 0x40000000
(mbs, mbr) = quotRem gbr 0x100000
(kbs, bs) = quotRem mbr 0x400
以下是我运行它时的情况（注意：我使用-O2编译）：
$> cabal build -v
creating dist/build
creating dist/build/autogen
Building bfreq-0.1.0.0...
Preprocessing executable 'bfreq' for bfreq-0.1.0.0...
Building executable bfreq...
creating dist/build/bfreq
creating dist/build/bfreq/bfreq-tmp
/usr/bin/ghc --make -o dist/build/bfreq/bfreq -hide-all-packages -fbuilding-cabal-package -package-conf dist/package.conf.inplace -i -idist/build/bfreq/bfreq-tmp -i. -idist/build/autogen -Idist/build/autogen -Idist/build/bfreq/bfreq-tmp -optP-include -optPdist/build/autogen/cabal_macros.h -odir dist/build/bfreq/bfreq-tmp -hidir dist/build/bfreq/bfreq-tmp -stubdir dist/build/bfreq/bfreq-tmp -package-id base-4.5.0.0-40b99d05fae6a4eea95ea69e6e0c9702 -package-id boxes-0.1.3-e03668bca38fe3e879f9d695618ddef3 -package-id containers-0.5.3.1-80819105034e34d03d22b1c20d6fd868 -O -O2 -rtsopts -XHaskell98 ./bfreq.hs
[1 of 1] Compiling Main ( bfreq.hs, dist/build/bfreq/bfreq-tmp/Main.o )
Linking dist/build/bfreq/bfreq ...
$> cat /dev/urandom | head -c 9999999 > test_data
$> cat ./test_data | ./dist/build/bfreq/bfreq +RTS -sstderr
analyze data from stdin
bytes: 9 MBs 521 KBs read 9999999 bytes
frequencies:
'\137' (137): 0.40% (39642)
'H' (72): 0.40% (39608)
<...>
'L' (76): 0.39% (38617)
'\246' (246): 0.39% (38609)
'I' (73): 0.38% (38462)
'q' (113): 0.38% (38437)
9,857,106,520 bytes allocated in the heap
14,492,245,840 bytes copied during GC
3,406,696,360 bytes maximum residency (13 sample(s))
14,691,672 bytes maximum slop
6629 MB total memory in use (0 MB lost due to fragmentation)
Tot time (elapsed) Avg pause Max pause
Gen 0 18348 colls, 0 par 10.90s 10.90s 0.0006s 0.0180s
Gen 1 13 colls, 0 par 15.20s 19.65s 1.5119s 12.6403s
INIT time 0.00s ( 0.00s elapsed)
MUT time 14.45s ( 14.79s elapsed)
GC time 26.10s ( 30.56s elapsed)
EXIT time 0.00s ( 0.00s elapsed)
Total time 40.55s ( 45.35s elapsed)
%GC time 64.4% (67.4% elapsed)
Alloc rate 682,148,818 bytes per MUT second
Productivity 35.6% of total user, 31.9% of total elapsed
除非我误解了上面的调试输出，否则我的程序使用了6 GB的内存？测试数据不到10 MB，这是怎么回事？
对于如何处理这种Haskell问题的一般建议也很好。换句话说，我应该避免在这种I/O中心的情况下使用Haskell吗？我应该使用pipes库来处理这种事情吗？
编辑： 感谢您的帮助，正确导入IntMap的严格版本可以解决内存问题。
我无法使性能分析（-fprof-auto）起作用，因为似乎我的所有包都没有为性能分析编译。我通过安装适用于我的操作系统（Ubuntu：ghc-prof）的GHC性能分析包来解决缺少基本库的性能分析问题，但根据此处所述，我需要手动重新安装所有Haskell库以进行性能分析。我现在没有时间做这件事，所以我只是把这个链接放在这里，以便任何有类似问题的人受益。
statusUpdater中，你有一个无限循环，这可以使用Control.Monad.forever实现。 - YellPikafindWithDefault），然后修改它（insert）来处理IntMap。IntMap提供了一个alter函数，可以一次完成您想要做的操作。 - YellPika