SevenThunders wrote:
Before I post this as a bug, I thought I'd check to make sure I'm not doing something wrong. For this test case, on my windows XP machine I create a simple Haskell routine that counts the characters in a file, create a DLL for that routine and call it from C. The C code gives the correct answer (I think) but then proceeds to hang and never terminate.
I wonder if you're hitting this bug: http://hackage.haskell.org/trac/ghc/ticket/926 if so, it's slightly worrying that the same thing happens if you just link your program directly to the DLL, rather than loading it explicitly. Cheers, Simon
If the readFile call is removed from this code, and a constant output is assigned to the variable ll, the code works fine and terminates correctly. Thus the bug may possibly be some kind of interaction with the file IO routine, if it's a bug at all.
First the Haskell code:
baddll.hs:
module Bad where import Foreign.Ptr import Foreign.C.String import Foreign.C.Types (CInt, CDouble )
foreign export stdcall badfunc :: CString -> IO (CInt) -- -- | Conversion from Int to CInt mkCInt :: Int -> CInt mkCInt n = fromIntegral n
badfunc fstr = do file <- peekCAString fstr sstr <- readFile file let ll = length sstr return $ mkCInt ll
The C code: #include
__declspec(dllimport) int __stdcall badfunc(char *outfile) ; int main(int argc, char *argv) { int ll ; ll = badfunc("bad.txt") ; printf("ll = %d\n", ll) ; return(1) ; }
The .bat file used to compile everything. (Assumes ghc and MS VC++ 6.0 is in my path) baddll.bat:
ghc -O2 -static -c baddll.hs -fglasgow-exts ghc -c dllBad.c ghc --mk-dll -static -fglasgow-exts -o baddll.dll dllBad.o baddll.o baddll_stub.o -L"." -L"." -optdll--def -optdllbaddll.def lib /def:baddll.def /MACHINE:X86 cl baddll.c baddll.lib
The .def file used to create the dll export symbols. baddll.def LIBRARY baddll.dll EXPORTS badfunc@4 badfunc = badfunc@4
The boilerplate code to load and unload the Haskell runtime inside the DLL. dllBad.c #include
#include extern void __stginit_Bad(void);
static char* args[] = { "ghcDll", NULL }; /* N.B. argv arrays must end with NULL */ BOOL STDCALL DllMain ( HANDLE hModule , DWORD reason , void* reserved ) { if (reason == DLL_PROCESS_ATTACH) { /* By now, the RTS DLL should have been hoisted in, but we need to start it up. */ startupHaskell(1, args, __stginit_Bad); return TRUE; }
if (reason == DLL_PROCESS_DETACH) { shutdownHaskell(); return TRUE; }
return TRUE; }
The text file I read in. bad.txt:
Greetings Earthlings
If I recall correctly, from another piece of test code, this seemed to work OK in GHC 6.4. However, I'll have to resurrect my GHC 6.4 installation to verify this. If anyone sees an obvious problem with my code I'd love to be informed about this.