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

[Karl Cronburg]

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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