【发布时间】：2013-12-31 01:19:52
【问题描述】：
我是 Haskell 新手，我不知道这个程序的表现如何如此糟糕。我尝试在各个地方强制使用严格的变量，但似乎没有什么不同。
这是我的代码（这个程序的目的是产生从标准输入中找到的输入字节的频率）：
{-# 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
这是我运行它时发生的情况（注意：我正在使用 -O2 进行编译）：
$> 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
所以除非我误解了上述调试输出，否则我的程序使用的是 6 GB？ 测试数据不到10MB，怎么回事？
任何关于如何在 Haskell 中解决此类问题的一般建议也很好。换句话说，对于这种以 I/O 为中心的东西，我应该避免使用 Haskell 吗？我应该为这种事情使用管道库吗？
编辑： 感谢您的帮助，正确导入 IntMap 的严格版本修复了内存问题。
我无法让分析 (-fprof-auto) 工作，因为我的包似乎都没有为分析而编译。我通过为我的操作系统安装 ghc 分析包（ubuntu：ghc-prof）解决了缺少分析基础库的问题，但根据this，我需要手动重新安装所有用于分析的haskell 库。我现在没有时间做这个，所以我只是把这个链接放在这里，以帮助有类似问题的任何人。
【问题讨论】：
-
您是否尝试过分析它以找出哪些函数占用了如此多的内存？很可能只有一个函数在消耗内存，所以一旦你知道是哪个函数，就会更容易找到内存泄漏。
-
一般准则：如果标准库函数可以满足您的需求，那么就使用它——它可能实现得更好。在您的
statusUpdater中，您有一个可以使用Control.Monad.forever实现的无限循环。 -
另外：在您的
run函数中，您通过首先查找值 (findWithDefault)，然后修改它 (insert) 来处理IntMap。IntMap提供了一个alter函数，可以一次完成你想做的事情。
标签： performance haskell