[reactive] whenE uses much memory

[Conal Elliott]

Richard,

Wow and wow!

I'm going to learn about hades.

   - Conal

On Wed, Aug 25, 2010 at 8:26 AM, Richard Smith <richard at metafoo.co.uk>wrote:

> Hi,
>
> On Tue, August 24, 2010 10:14, Alexander Foremny wrote:
> > When running worldB from main I can see the program's memory usage
> > increasing and everything becomes very unresponsive. It seems as if whenE
> > is accumalating all the occurences of the event. The problem seems to
> boil
> > down to snapshot having the same behavior.
> >
> >> snapshot (pure False) (atTimes [1..])
> >
> > This piece of code uses very much memory either. Is this due to
> > reactive being broken (I read that somewhere) or is my solution just no
> > solution at all?
> >
> > I am using ghc 6.12.1 with reactive 0.11.5 and reactive-glut 0.1.9.
>
> Shameless plug alert...
>
> I've attached my Haskell debugger hades <http://control.monad.st/> to the
> following testcase:
>
> import Control.Applicative
> import FRP.Reactive
> import FRP.Reactive.LegacyAdapters
>
> foo = snapshot_ (pure (putStrLn "Hi")) (atTimes [0.001,0.002..])
> main = adaptE foo >> adaptE foo
>
> Curious as to what is being retained, I did some poking around in the
> heap. Here's what I've found:
>
> [... snip looking through backtrace ...]
> > liftIO . putStr =<< prettyPrint 140513828164552
> $1 = foo/s2fC
> > pointers 140513828164552
> [Ptr (RemotePtr 8279928),Ptr (RemotePtr 8324640)]
> > liftIO . putStr =<< prettyPrint 8279928
> $1 = (,) (Imp $134 (exactNB/smWn $138 $133 $134)) (Stepper $141 ((,) (Imp
> $140 (exactNB/smWn $138 $139 $140)) (Stepper $141 ((,) (Imp $143
> (exactNB/smWn $138 $142 $143)) (Stepper $141 ((,) (Imp $145 (exactNB/smWn
> $138 $144 $145)) (Stepper $141 ((,) (Imp $147 (exactNB/smWn $138 $146
> $147)) (Stepper $141 ((,) (Imp $149 (exactNB/smWn $138 $148 $149))
> (Stepper $141 ((,) (Imp $151 (exactNB/smWn $138 $150 $151)) (Stepper $141
> ((,) (Imp $153 (exactNB/smWn $138 $152 $153)) ([...snip...]
> [...]
> $133 = 1.0e-3
> $134 = (NoBound $133)
> $135 = 'H'
> $136 = (FileHandle $80 $81)
> $137 = (hPutStr1 $120 ((,) NoBuffering $121) $122 (hPutStr2 $123 $124)
> (hPutStr_$s$wa1 $127 $126) (hPutStr_$s$wa $127 $128))
> $138 = (<instance field OrdAddBounds_<=> $2 (amb2 (forkIO2 (childHandler1
> $24 $25 $26 $27 ($Lr3Ktlvl23 $23))) $31 (catches1 $31) (finally1 $31)
> ((Handler $32 writeWord64OffPtr1/r1uF):((Handler $131
> writeWord64OffPtr1/r1uJ):((Handler (<dict for Exception> $53 $54 ($LrXBa7
> $52) $57) (<instance field ShowNonTermination2>/r1uL)):((Handler $132
> $Lr1yylvl1/r1uP):((Handler (<dict for Exception> $75 $76 ($LrXVa12 $74)
> $79) ($Lr1yylvl1/r1uR (writeWord64OffPtr1/r1uD $136 $123 $137 $129
> '"':$130))):$9))))) (SomeException $131 BothBottom) (SomeException $132
> DontBother)))
> $139 = 2.0e-3
> $140 = (NoBound $139)
> $141 = (main8 $123 $135:$50:$9 $136 $137)
> $142 = 3.0e-3
> $143 = (NoBound $142)
> $144 = 4.0e-3
> $145 = (NoBound $144)
> $146 = 5.0e-3
> $147 = (NoBound $146)
> $148 = 6.0e-3
> $149 = (NoBound $148)
> $150 = 7.0e-3
> $151 = (NoBound $150)
> $152 = 8.0e-3
> $153 = (NoBound $152)
>
> So (obviously in retrospect), foo is retaining an object of this form:
>
> (Imp (exactNB/smWn (NoBound 1.0e-3)), Stepper main8
>  (Imp (exactNB/smWn (NoBound 2.0e-3)), Stepper main8 (..., ...)))
>
> Here, main8 looks to be the (putStrLn "Hi") computation.
>
>
> A slight tweak to the code should sort this out:
>
> foo () = snapshot_ (pure (putStrLn "Hi")) (atTimes [0.001,0.002..])
> main = adaptE (foo ()) >> adaptE (foo ())
>
> Now I no longer see the space leak. In hades, I can't even find a
> reference to foo (presumably it got inlined out of existence). The event's
> list now looks like this (start from $209):
>
> $195 = 25.91600000000869
> $196 = (NoBound $195)
> $209 = listEG/sigh $210 $211
> $210 = (Imp $196 (exactNB/smWn $216 $195 $196))
> $211 = <instance field FunctorEventG_fmap>/siFL (withTimeE1 $212) $213
> $212 = exactNB1
> $213 = listEG/sigh $210 (Stepper () $214)
> $214 = <worker for untilE>/sgyB $215 (<worker for untilE>/sfAZ $228 (Imp
> $227 (atTimes3 $216)))
> $215 = foldr/s2p1 (atTimes1 $216) $217
> $216 = (<instance field OrdAddBounds_<=> $204 $201)
> $217 = <worker for %>/s8ah $195 25.91700000000869 $218 $219 (<worker for
> %>/s3ts $218 $219)
> $218 = plusDouble
> $219 = minusDouble
>
>
> I hope this gives you enough insight to be able to fix your code!
>
> Regards,
> Richard Smith
>
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