Re: [GHC] #9520: Running an action twice uses much more memory than running it once

28 Aug 2014

      #9520: Running an action twice uses much more memory than running it once
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              Reporter:  snoyberg    |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.3
            Resolution:              |         Keywords:
      Operating System:  Linux       |     Architecture:  x86_64 (amd64)
       Type of failure:  Runtime     |       Difficulty:  Unknown
  performance bug                    |       Blocked By:
             Test Case:              |  Related Tickets:
              Blocking:              |
Differential Revisions:              |
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Comment (by snoyberg):

 Apologies if this is becoming repetitive, but here's a slightly simpler
 version demonstrating the same issue:

 {{{#!hs
 import System.IO

 data Sink i r = Sink (i -> Sink i r) r

 sinkCount :: Sink i Int
 sinkCount =
     loop 0
   where
     loop cnt = Sink (\_ -> loop $! cnt + 1) cnt

 feed :: Handle -> Sink Char r -> IO r
 feed h =
     loop
   where
     loop (Sink f g) = do
         eof <- hIsEOF h
         if eof
             then return g
             else do
                 c <- hGetChar h
                 loop $! f c

 action :: IO ()
 action = withBinaryFile "1mb" ReadMode $ \h -> do
     feed h sinkCount
     return ()

 main :: IO ()
 main = do
     action
     action
 }}}

 The following code, however, does *not* demonstrate the problem:

 {{{#!hs
 import System.IO

 data Sink i r = Sink (i -> Sink i r) r

 sinkCount :: Sink i Int
 sinkCount =
     loop 0
   where
     loop cnt = Sink (\_ -> loop $! cnt + 1) cnt

 feed :: Sink Char r -> IO r
 feed =
     loop 10000000
   where
     loop 0 (Sink _ g) = return g
     loop i (Sink f _) = loop (i - 1) (f 'A')

 action :: IO ()
 action = do
     feed sinkCount
     return ()

 main :: IO ()
 main = do
     action
     action
 }}}

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9520#comment:4
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