[GHC] #12889: memory leak

28 Nov 2016

      #12889: memory leak
-------------------------------------+-------------------------------------
           Reporter:  zoranbosnjak   |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 This simple test program leaks memory for no obvious reason.

 {{{#!hs
 module Main where

 import Control.Monad
 import Control.Monad.Trans.Reader

 main :: IO ()
 main = do
     runReaderT task ()
     main

 task :: ReaderT () IO ()
 task = forM_ [(1::Integer)..] $ \cnt -> do
     return cnt

 }}}

 However, there are some minor changes that (each individual change alone)
 make this program run in constant memory.

 1. If I remove
 {{{#!hs
 module Main where
 }}}

 2. If I remove recursive call to main

 3. If I put task definition under the scope of main, like so
 {{{#!hs

 module Main where

 import Control.Monad
 import Control.Monad.Trans.Reader

 main :: IO ()
 main = do
     runReaderT task ()
     main
   where
     task :: ReaderT () IO ()
     task = forM_ [(1::Integer)..] $ \cnt -> do
         return cnt
 }}}

 Any of the changes above make the program run OK, but I belive that this
 should be also true for the original test program. I am not sure where the
 problem is (if at all), but it's extremely difficult to isolate this kind
 of problem in the real application.

 Please check if anything can be done on the compiler or runtime to prevent
 this kind of problems.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12889
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