[Fwd: Memory corruption issues when using newAlignedPinnedByteArray, GC kicking in?]
nicolas at incubaid.com
Wed Jul 11 00:03:29 CEST 2012
I sent this mail to Haskell Cafe earlier today, and was pointed  at
this list. As such...
Any help/advice would be greatly appreciated!
-------- Forwarded Message --------
> From: Nicolas Trangez <nicolas at incubaid.com>
> To: haskell-cafe at haskell.org
> Cc: Roman Leshchinskiy <rl at cse.unsw.edu.au>
> Subject: Memory corruption issues when using
> newAlignedPinnedByteArray, GC kicking in?
> Date: Tue, 10 Jul 2012 19:20:01 +0200
> 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 .
> I also use 3 different versions of mallocVector (depending on
> compile-time flags):
> mallocVectorOrig : This is the upstream version, discarding the
> integer argument I added.
> Then here's my first attempt, very similar to the implementation of
> mallocPlainForeignPtrBytes  at  using GHC.* libraries.
> Finally there's something similar at  which uses the 'primitive'
> 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)
>  https://gist.github.com/3084806#LC37
>  https://gist.github.com/3084806#LC119
>  https://gist.github.com/3084806#LC100
>  https://gist.github.com/3084806#LC81
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