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Today's Topics:
1. How to hunt this space-leak (martin)
2. State Monad in constant space? (martin)
3. Re: How to hunt this space-leak (Romain G?rard)
----------------------------------------------------------------------
Message: 1
Date: Sun, 12 Jun 2016 15:38:02 +0200
From: martin <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] How to hunt this space-leak
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Hello all,
I hope I am not asking for too much, as to explain my problem, you need to read
my code, which may not be a pleasure.
I am trying to write a "Logger", which formats and accumulates log-entries in a
monoid. From there I went to writing an
"accumulating" logger, i.e. one which can accumulate (sum/avg) over entries
made with a certain timespan.
My problen is memory consumption. In the test below I stress the logger with 1
million values, but in the end result,
there are only 10 entries left, because it accumulates over 100,000. Memory
goes up to apx 100MB.
When I comment out the line, which logs the accumulated value (see -- > below),
memory stays below 10MB. I dont
understand why this is so. After all, the difference is only whether or not
those 10 entries are logged or not.
Can someone explain this?
{-# LANGUAGE BangPatterns#-}
import Data.Monoid
import Control.Monad.State.Strict
import System.TimeIt
import Text.Show.Pretty
import Debug.Trace
------------------------------------------------------------
-- Simple Time Stuff
------------------------------------------------------------
type Instant = Double
type Interval = Double
type Timed a = (Instant, a)
instant = fst
------------------------------------------------------------
-- Logger based on State monad
------------------------------------------------------------
data SLogger a l = SLgr {runSLogger :: a ->State l (SLogger a l)}
type SLogFormatter a l = a -> l
accLogger :: (Monoid c, Show a) =>
(Instant, Interval, [Timed b]) ->
SLogFormatter (Timed a) [Timed b] -> SLogFormatter [Timed b]
[Timed c] -> SLogger (Timed a) [Timed c]
accLogger (tx, dt, tas) fmt1 fmt2 = SLgr $ \(!ta) ->
let x = fmt1 ta
!tas' = x <> tas
in
if instant ta < tx
then do
-- keep accumulating
return $ accLogger (tx, dt, tas')
fmt1 fmt2
else do
-- compute new log and reset
accumulator
!l0 <- get
-- > put $ fmt2 tas' <> l0
return $ accLogger ((tx+dt), dt,
[]) fmt1 fmt2
accFmt1 ta = [ta]
accFmt2 tas = [(fst $ head tas, "hello from accFormatter")]
-- apply logger to a list of as
stest lgr [] = return lgr
stest lgr (a:as) = do
lgr' <- (runSLogger lgr) a
stest lgr' as
main2 = do
let as = zip [1.0 .. 1000000.0] [1..1000000] :: [(Instant, Int)]
log = execState (stest (accLogger (100000.0,100000.0,[]) accFmt1
accFmt2 ) as) [(0,"init")]
timeIt $ putStrLn $ ppShow log
putStrLn "done"
main = main2
------------------------------
Message: 2
Date: Sun, 12 Jun 2016 23:11:05 +0200
From: martin <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] State Monad in constant space?
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Hello all,
the State Monad wraps around a computation s -> (s,a). Inside a do block I am
actually assembling such a computation.
Now when I do this many times, i.e. in a recursice call, I am builing a huge
expression
m a >>= (\a -> mb) >>= (\b -> mc) ...
The result of this expression is a function s -> (s,a). But I cannot see how
the space for this expression can be
reclaimed, and how it could ever run in constant space. Once I call runState
and I provide an initial s, I have some
hope, but before?
How is this supposed to work? How do I avoid allocating space for this huge
expression?
------------------------------
Message: 3
Date: Mon, 13 Jun 2016 13:13:39 +0200
From: Romain G?rard <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] How to hunt this space-leak
Message-ID: <[email protected]>
Content-Type: text/plain; charset=UTF-8; format=flowed
Hello,
I have used the technique described below[1] with great success.
To be fair, debugging space leak in haskell is kinda hard, even knowing
that you have one is a big step forward.
Maybe it is possible to create a program like valgrind for haskell, but
I lack the knowledge to tell if it's possible or not.
[1] http://neilmitchell.blogspot.fr/2015/09/detecting-space-leaks.html
Regards
Le 2016-06-12 15:38, martin a ?crit?:
> Hello all,
>
> I hope I am not asking for too much, as to explain my problem, you
> need to read my code, which may not be a pleasure.
>
> I am trying to write a "Logger", which formats and accumulates
> log-entries in a monoid. From there I went to writing an
> "accumulating" logger, i.e. one which can accumulate (sum/avg) over
> entries made with a certain timespan.
>
> My problen is memory consumption. In the test below I stress the
> logger with 1 million values, but in the end result,
> there are only 10 entries left, because it accumulates over 100,000.
> Memory goes up to apx 100MB.
>
> When I comment out the line, which logs the accumulated value (see --
> > below), memory stays below 10MB. I dont
> understand why this is so. After all, the difference is only whether
> or not those 10 entries are logged or not.
>
> Can someone explain this?
>
>
>
> {-# LANGUAGE BangPatterns#-}
>
>
> import Data.Monoid
> import Control.Monad.State.Strict
> import System.TimeIt
> import Text.Show.Pretty
> import Debug.Trace
>
>
> ------------------------------------------------------------
> -- Simple Time Stuff
> ------------------------------------------------------------
> type Instant = Double
> type Interval = Double
> type Timed a = (Instant, a)
> instant = fst
>
> ------------------------------------------------------------
> -- Logger based on State monad
> ------------------------------------------------------------
>
> data SLogger a l = SLgr {runSLogger :: a ->State l (SLogger a l)}
> type SLogFormatter a l = a -> l
>
>
> accLogger :: (Monoid c, Show a) =>
> (Instant, Interval, [Timed b]) ->
> SLogFormatter (Timed a) [Timed b] -> SLogFormatter [Timed
> b] [Timed c] -> SLogger (Timed a) [Timed c]
>
>
> accLogger (tx, dt, tas) fmt1 fmt2 = SLgr $ \(!ta) ->
> let x = fmt1 ta
> !tas' = x <> tas
> in
> if instant ta < tx
> then do
> -- keep accumulating
> return $ accLogger (tx,
> dt, tas') fmt1 fmt2
> else do
> -- compute new log and
> reset accumulator
> !l0 <- get
> -- > put $ fmt2 tas' <> l0
> return $ accLogger
> ((tx+dt), dt, []) fmt1 fmt2
>
>
>
> accFmt1 ta = [ta]
> accFmt2 tas = [(fst $ head tas, "hello from accFormatter")]
>
> -- apply logger to a list of as
> stest lgr [] = return lgr
> stest lgr (a:as) = do
> lgr' <- (runSLogger lgr) a
> stest lgr' as
>
>
> main2 = do
> let as = zip [1.0 .. 1000000.0] [1..1000000] :: [(Instant, Int)]
> log = execState (stest (accLogger (100000.0,100000.0,[])
> accFmt1 accFmt2 ) as) [(0,"init")]
> timeIt $ putStrLn $ ppShow log
> putStrLn "done"
>
>
>
> main = main2
>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
------------------------------
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