Haskell DLL (using FFI) causes memory leak.

Vanessa McHale vanessa.mchale at iohk.io
Mon Aug 27 15:00:13 UTC 2018

I don't know about C++, but I do know that when calling Haskell from C
code one must initialize the runtime and then exit it once finished. I
also know that one must only initialize the runtime once over the course
of the program's run. As far as I can tell, this does not occur in your

On 08/27/2018 09:44 AM, Ольга Филиппская wrote:
> Hello.
> /Summary: /memory is consumed without releasing when a Haskell DLL
> (that uses FFI) is loaded and unloaded in an endless loop.
> /Details/: I'm working on a C++ project relying on a DLL that uses
> Haskell code. The DLL was built with GHC 8.0.1 x64, OS is Windows 7.
> (Newer versions of GHC - 8.2.1 and later - do not allow you to build
> such DLLs due to some bugs: ticket #1
> <https://ghc.haskell.org/trac/ghc/ticket/14472#no2>, ticker #2
> <https://ghc.haskell.org/trac/ghc/ticket/14784#no1>). The C++ project
> was built with MSVC compiler 2015.
> We noticed that memory is not released when the library is unloaded.
> I've constructed a baseline example to reproduce the bug. It has three
> files: the first one is *HaskellSources.hs*(see attachments). It
> contains one foreign export function foo. This foreign export function
> is necessary to reproduce the bug. The second file is *CWrapper.cpp*.
> I intentionally didn't include any Haskell function export because
> they make no difference for this example. The last file is the code of
> the main program (see *main.cpp*) that loads the library and unloads
> it at once in an endless loop.
> There are two cases: whether HaskellExports.o is included into the
> library or not.
> 1. HaskellExports.o is not included into the library (see attached
> build script/ build_no_hs.sh/). Everything works just fine (i.e.
> amount of memory consumed by the app is the same before DLL loading
> and right after unloading.)
> 2. HaskellExports.o is included into the library
> (see /build_w_hs.sh/). Memory is not released after unloading the DLL,
> after repeated load/unload cycles memory consumption keeps growing
> until finally the application crashes.
> Is this a known problem? Is it tracked in your bugtracker? (Or maybe
> it is not a problem at all and I'm doing it wrong).
> Thank you for your time.
> -- 
> /
> Olga Philippskaya
> ./
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