All, I sent this mail to Haskell Cafe earlier today, and was pointed [1] at this list. As such...
Any help/advice would be greatly appreciated! Thanks, Nicolas [1] http://www.haskell.org/pipermail/haskell-cafe/2012-July/102242.html -------- Forwarded Message -------- > From: Nicolas Trangez <nico...@incubaid.com> > To: haskell-c...@haskell.org > Cc: Roman Leshchinskiy <r...@cse.unsw.edu.au> > Subject: Memory corruption issues when using > newAlignedPinnedByteArray, GC kicking in? > Date: Tue, 10 Jul 2012 19:20:01 +0200 > > All, > > While working on my vector-simd library, I noticed somehow memory I'm > using gets corrupted/overwritten. I reworked this into a test case, and > would love to get some help on how to fix this. > > Previously I used some custom FFI calls to C to allocate aligned memory, > which yields correct results, but this has a significant (+- 10x) > performance impact on my benchmarks. Later on I discovered the > newAlignedPinnedByteArray# function, and wrote some code using this. > > Here's what I did in the test case: I created an MVector instance, with > the exact same implementation as vector's > Data.Vector.Storable.Mutable.MVector instance, except for basicUnsafeNew > where I pass one more argument to mallocVector [1]. > > I also use 3 different versions of mallocVector (depending on > compile-time flags): > > mallocVectorOrig [2]: This is the upstream version, discarding the > integer argument I added. > > Then here's my first attempt, very similar to the implementation of > mallocPlainForeignPtrBytes [3] at [4] using GHC.* libraries. > > Finally there's something similar at [5] which uses the 'primitive' > library. > > The test case creates vectors of increasing size, then checks whether > they contain the expected values. For the default implementation this > works correctly. For both others it fails at some random size, and the > values stored in the vector are not exactly what they should be. > > I don't understand what's going on here. I suspect I lack a reference > (or something along those lines) so GC kicks in, or maybe the buffer > gets relocated, whilst it shouldn't. > > Basically I'd need something like > > GHC.ForeignPtr.mallocPlainAlignedForeignPtrBytes :: Int -> Int -> IO > (ForeignPtr a) > > Thanks, > > Nicolas > > [1] https://gist.github.com/3084806#LC37 > [2] https://gist.github.com/3084806#LC119 > [3] > http://hackage.haskell.org/packages/archive/base/latest/doc/html/src/GHC-ForeignPtr.html > [4] https://gist.github.com/3084806#LC100 > [5] https://gist.github.com/3084806#LC81 > > _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
