Segfault when doing hs_init()/hs_exit() multiple times

Wed Dec 2 19:58:56 UTC 2015

Upon further investigation:

    *"The FFI spec requires the implementation to support re-initialising
itself after being shut down with hs_exit(), but GHC does not currently
support that."*

https://downloads.haskell.org/~ghc/7.10.2/docs/html/users_guide/bugs-and-infelicities.html#infelicities-ffi

So it's a known issue / shortcoming.

-Karl Cronburg-

On Wed, Dec 2, 2015 at 2:41 PM, Karl Cronburg <karl.cronburg at gmail.com>
wrote:

> I was having the same problem a while back. If you turn on debugging
> symbols and give it to gdb, you
> get that the seg fault is happening when the RTS attempts to allocate
> after the second initialization:
>
>     Program received signal SIGSEGV, Segmentation fault.
>     0xf7f6f4f9 in allocate (cap=cap at entry=0xf7f92b40 <MainCapability>,
> n=n at entry=2) at rts/sm/Storage.c:812
>     812 rts/sm/Storage.c: No such file or directory.
>     (gdb) bt
>     #0  0xf7f6f4f9 in allocate (cap=cap at entry=0xf7f92b40
> <MainCapability>, n=n at entry=2) at rts/sm/Storage.c:812
>     #1  0xf7f5c603 in rts_mkInt32 (cap=0xf7f92b40 <MainCapability>,
> i=-11921) at rts/RtsAPI.c:69
>     #2  0xf7cdea7a in pointer_test () from ../../ia32/build/
> libHSpads-haskell-1.1-6fKCdLtCMO82em71etbiu1-ghc7.10.2.so
>     #3  0x5655579c in main (argc=1, argv=0xffffd244) at Pointer.c:11
>
> So my solution was to just leave the RTS initialized. What's the downside
> of leaving it initialized throughout
> the entire execution of your program? If the RTS / GC is smart enough it
> should know not to waste time
> doing a GC when no Haskell code has been run?
>
> I too would be interested though in being able to clean up the RTS from C
> when I know no Haskell code will
> be run again anytime soon.
>
> -Karl Cronburg-
>
> On Wed, Dec 2, 2015 at 1:58 PM, Alp Mestanogullari <alpmestan at gmail.com>
> wrote:
>
>> Hello everyone,
>>
>> I'm currently calling Haskell code from C. My goal is to apply a Haskell
>> function to each element of some dataset that I get from outside
>> Haskell-land. For now, before I make this fancier and more efficient, the
>> plan is to just bring the RTS up with hs_init, call my Haskell function
>> (exporter to C with 'foreign export ccall [...]') on the element and
>> finally shut the RTS down, doing this for every element.
>>
>> When running this, I realized the RTS was running into a segfault when
>> calling the Haskell function on the second element. This led me to believe
>> it wasn't possible to call hs_init()/hs_exit() multiple times in the same
>> program. But then I checked the Haskell 2010 report, FFI section [1], and
>> it says:
>>
>> *The function hs_init() initialises the Haskell system and provides it
>> with the available command line arguments. Upon return, the arguments
>> solely intended for the Haskell runtime system are removed (i.e., the
>> values that argc and argv point to may have changed). This function must be
>> called during program startup before any Haskell function is invoked;
>> otherwise, the system behaviour is undefined. Conversely, the Haskell
>> system is deinitialised by a call to hs_exit(). Multiple invocations of
>> hs_init() are permitted, provided that they are followed by an equal number
>> of calls to hs_exit() and that the first call to hs_exit() is after the
>> last call to hs_init(). In addition to nested calls to hs_init(), the
>> Haskell system may be de-initialised with hs_exit() and be re-initialised
>> with hs_init() at a later point in time. This ensures that repeated
>> initialisation due to multiple libraries being implemented in Haskell is
>> covered. *
>>
>> Which means, if I understand correctly, that what I want, while very
>> inefficient, should work fine.
>>
>> I've put together a minimal example that exhibits the problem, which can
>> be found at https://github.com/alpmestan/simple-c-export :
>>
>> - https://github.com/alpmestan/simple-c-export/blob/master/run-haskell.c
>> shows the C code that brings the RTS up and down, with some printf
>> statements to show what's going on.
>>
>> - https://github.com/alpmestan/simple-c-export/blob/master/Foo.hs shows
>> the trivial Haskell function I'm exposing.
>>
>> -
>> https://github.com/alpmestan/simple-c-export/blob/master/simple-c-export.cabal
>> contains the build options I'm compiling the code with
>>
>> When running this on my machine (OS X, ghc 7.8.3 and 7.10.2), I always
>> get:
>>
>> $ cabal run simple-c
>> Preprocessing executable 'simple-c' for simple-c-export-0.1...
>> Linking dist/build/simple-c/simple-c ...
>> Running simple-c...
>> #0 - Launching RTS...
>> #0 - RTS started! Calling Haskell function...
>> 0
>> #0 - Killing RTS now...
>> #0 - RTS killed!
>> #1 - Launching RTS...
>> #1 - RTS started! Calling Haskell function...
>> Segmentation fault: 11
>>
>> Is there something special I should do to make this work, that I'm
>> overlooking? Or is this a bug (that I should report on Trac, I guess) ?
>>
>> Thanks in advance for any clarification on this.
>>
>> --
>> Alp Mestanogullari
>>
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>>
>>
>
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