Memory leak in Fudgets

3 Mar 2006

      I wrote a very simple Fudgets program (just copies stdin to stdout, no
graphics involved)

-------- leaktest.hs ------------------

module Main where

import Graphics.UI.Fudgets.Fudgets

main = fudlogue (stdoutF >==< stdinF)

and ran it like this:

yes | leaktest

I found out that the program grows in memory. Its "traditional" analog:

-------- leaktest2.hs -----------------

module Main where

import System.IO

main = do hGetLine stdin >>= hPutStrLn stdout
main

works in constant space.

I tried to observe the GC realtime stats with +RTS -Sstderr -M600K

It turns out, garbage is collected, number of allocated and collected
bytes are mostly constant, and number of live bytes fluctuates, but
averagely stays the same:

    Alloc    Collect    Live    GC    GC     TOT     TOT  Page Flts
    bytes     bytes     bytes  user  elap    user    elap
   316720    262144      9528  0.00  0.00    0.02    0.02  144  499  (Gen:  0)
   262128    262144     22188  0.01  0.01    0.03    0.04    0    3  (Gen:  0)
   262128    262144      8276  0.00  0.00    0.04    0.05    0    0  (Gen:  0)
   262128    262144     24612  0.01  0.01    0.05    0.06    0    0  (Gen:  0)
   262128    262144     10680  0.00  0.00    0.06    0.07    0    0  (Gen:  0)
   262128    262144     23376  0.00  0.00    0.06    0.08    0    0  (Gen:  0)
   262128    262144      9444  0.00  0.00    0.07    0.09    0    0  (Gen:  0)
   262012    262144     25492  0.00  0.00    0.07    0.10    0    0  (Gen:  0)

... program grows to 10M .........

   262128    262144      1684  0.01  0.01   42.33   66.10    0    0  (Gen:  0)
   262128    262144     13396  0.01  0.01   42.34   66.11    0    0  (Gen:  0)
   262124    262144     25540  0.01  0.01   42.35   66.12    0    0  (Gen:  0)
   262128    262144     11988  0.00  0.00   42.35   66.13    0    0  (Gen:  0)
   262128    262144      1760  0.00  0.00   42.36   66.14    0    0  (Gen:  0)
   262128    262144     14464  0.00  0.00   42.37   66.15    0    0  (Gen:  0)
   262128    262144      1656  0.00  0.00   42.37   66.16    0    0  (Gen:  0)

.... and was interrupted ...........

1,614,769,480 bytes allocated in the heap
 78,801,952 bytes copied during GC
     25,624 bytes maximum residency (6160 sample(s))

       6160 collections in generation 0 ( 10.35s)

          1 Mb total memory in use

  INIT  time    0.01s  (  0.00s elapsed)
  MUT   time   32.01s  ( 55.38s elapsed)
  GC    time   10.35s  ( 10.78s elapsed)
  EXIT  time    0.00s  (  0.00s elapsed)
  Total time   42.37s  ( 66.16s elapsed)

  %GC time      24.4%  (16.3% elapsed)

  Alloc rate    50,430,027 bytes per MUT second

  Productivity  75.5% of total user, 48.4% of total elapsed

So, what could be the reason of such memory leak? What else may grow
if the heap remains constant? How can it be observed?

Any ideas are welcome.

--
Dimitry Golubovsky

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