Unreproducible failure in Unicode.Stream test suite

[harendra-kumar]

On GHC-8.6.5, in a PR based on 5d096dfad

Failures:

  Streamly/Test/Unicode/Stream.hs:177:9: 
  1) Unicode.Stream, UTF8 - Encoding / Decoding, Arrays Streamly.Data.String.lines == Prelude.lines
       Assertion failed (after 766 tests):
      zipAsyncly Compose three - empty in the middle [✔]
         [48,89,237,128,185,236,161,51,229,204,167,5,154,15,252,80,71,15,179,204]

  To rerun use: --match "/Unicode.Stream/UTF8 - Encoding / Decoding/Arrays Streamly.Data.String.lines == Prelude.lines/" --seed 1380626044
        +++ OK, passed 100 tests.

Randomized with seed 1380626044

The relevant test is:

testLinesArray :: Property
testLinesArray =
    forAll genWord8 $ \list ->
        monadicIO $ do
            xs <- Stream.toList
                    $ fmap A.toList
                    $ AS.splitOnSuffix 10
                    $ Stream.fromPure (A.fromList list)
            assert (xs == map (map (fromIntegral . ord))
                              (lines (map (chr .  fromIntegral) list)))

Could be an issue with AS.splitOnSuffix?

{-# INLINE splitOnSuffix #-}
splitOnSuffix
    :: (MonadIO m)
    => Word8
    -> Stream m (Array Word8)
    -> Stream m (Array Word8)
splitOnSuffix = Array.compactOnByteSuffix

{-# INLINE compactOnByteSuffix #-}
compactOnByteSuffix
    :: (MonadIO m)
    => Word8
    -> Stream m (Array Word8)
    -> Stream m (Array Word8)
compactOnByteSuffix byte =
    fmap unsafeFreeze . MA.compactOnByteSuffix byte . fmap unsafeThaw

{-# INLINE compactOnByteSuffix #-}
compactOnByteSuffix
    :: (MonadIO m)
    => Word8
    -> Stream m (MutArray Word8)
    -> Stream m (MutArray Word8)
compactOnByteSuffix byte =
        -- XXX use spliceExp and rightSize?
        Stream.splitInnerBySuffix
            (\arr -> byteLength arr == 0) (breakOn byte) splice

breakOn uses unpinned pointer in memcpy, could it be because of that?

[harendra-kumar]

PR #2818 fixes the issue by using correct FFI semantics, avoiding garbage collection between getting a pointer and invoking FFI call.