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Fix memory leak in handleToFd, fixes issue #4 #222

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Fix memory leak in handleToFd, fixes issue #4 #222

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fdbf4ee
Fix memory leak in handleToFd, fixes issue #4
hasufell Jul 10, 2022
fce09fa
Fixes wasm CI
hasufell Jul 11, 2022
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23 changes: 21 additions & 2 deletions System/Posix/IO/Common.hsc
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
{-# LANGUAGE CApiFFI #-}
{-# LANGUAGE NondecreasingIndentation #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE Safe #-}
{-# LANGUAGE Trustworthy #-}

-----------------------------------------------------------------------------
-- |
Expand Down Expand Up @@ -73,7 +73,10 @@ import GHC.IO.Handle.Types
import qualified GHC.IO.FD as FD
import qualified GHC.IO.Handle.FD as FD
import GHC.IO.Exception
import GHC.IO.Buffer
import GHC.IORef
import Data.Typeable (cast)
import System.IO.Unsafe (unsafePerformIO)

#if !defined(HAVE_PIPE)
import System.IO.Error ( ioeSetLocation )
Expand Down Expand Up @@ -301,10 +304,26 @@ handleToFd' h h_@Handle__{haType=_,..} = do
-- converting a Handle into an Fd effectively means
-- letting go of the Handle; it is put into a closed
-- state as a result.
flushWriteBuffer h_

-- free the spare buffers
writeIORef haBuffers BufferListNil
writeIORef haCharBuffer noCharBuffer
writeIORef haByteBuffer noByteBuffer
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Doesn't this change lose any unwritten data in the write buffer? It used to be flushed, but now is just dropped?

With hClose this happens before the call to hClose_handle_ handle_ (after which the above code is modelled):

hClose_help :: Handle__ -> IO (Handle__, Maybe SomeException)
hClose_help handle_ =
  case haType handle_ of
      ClosedHandle -> return (handle_,Nothing)
      _ -> do mb_exc1 <- trymaybe $ flushWriteBuffer handle_ -- interruptible
                    -- it is important that hClose doesn't fail and
                    -- leave the Handle open (#3128), so we catch
                    -- exceptions when flushing the buffer.
              (h_, mb_exc2) <- hClose_handle_ handle_
              return (h_, if isJust mb_exc1 then mb_exc1 else mb_exc2)

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I'm really not too sure about this change. I think it's not necessary for 2.8.0.0, since people have lived with it for over a decade.

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If the memory leak can be safely avoided, I'm inclined to fix anyway, but replacing flush with just dropping the buffer is not correct. Otherwise, I don't see any issues.

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@hs-viktor I'm not too familiar with this part of the code. Feel free to adjust this PR.


-- release our encoder/decoder
closeTextCodecs h_

FD.release fd
return (Handle__{haType=ClosedHandle,..}, Fd (FD.fdFD fd))

{-# NOINLINE noCharBuffer #-}
noCharBuffer :: CharBuffer
noCharBuffer = unsafePerformIO $ newCharBuffer 1 ReadBuffer

{-# NOINLINE noByteBuffer #-}
noByteBuffer :: Buffer Word8
noByteBuffer = unsafePerformIO $ newByteBuffer 1 ReadBuffer


-- -----------------------------------------------------------------------------
-- Fd options
Expand Down
2 changes: 2 additions & 0 deletions cabal.project.wasm32-wasi
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Expand Up @@ -4,3 +4,5 @@ package unix
ghc-options: -Wno-unused-imports

write-ghc-environment-files: always

allow-newer: all:base