GHC 6.4.1 and Win32 DLLs: Bug in shutdownHaskell?

Michael Marte marte at
Wed Mar 1 12:49:37 EST 2006

Hello *,

before filing a bug report, I want others to comment on my problem. 
Maybe it's my fault, not ghc's.

I wrapped up some Haskell modules in a Win32 DLL.
Loading the DLL dynamically (with LoadLibrary) works fine. However, 
whether I actually use the library or not, the program (an application 
with MFC GUI) crashes upon termination.
To find the reason for the crash, I added a new function for unloading 
the DLL using FreeLibrary. FreeLibrary works fine, however the program 
crashes when it returns to the main event loop. Interestingly, when I 
reload the library (FreeLibrary followed by LoadLibrary) the program 
continues working. However, every reload cycle causes the virtual size 
of the process to increase by about 300K and the fourth reload fails 
with the error message "getMBlock: VirtualAlloc failed with: 8" (appears 
in a message window) accompanied by many repetitions of the message 
"Timer proc: wait failed -- error code: 6" (appears on stderr) and 
followed by the message "getMBlocks: misaligned block returned" (again 
in a message window). Then the programm crashes.

Development takes place on Windows XP Professional using MS Visual 
Studio 6.0 SP 5 and ghc 6.4.1. There are no references from the C++ side 
to the Haskell heap. I build the DLL using the command

ghc --mk-dll -optdll--def -optdllFoo.def -o Foo.dll Foo.o Foo_stub.o 

dllMain.c looks as follows:

#include <windows.h>
#include <Rts.h>

extern void __stginit_EUzu3820zu85(void);

static char* args[] = { "ghcDll", NULL };
                       /* N.B. argv arrays must end with NULL */
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_Foo);
        return TRUE;
    } else if (reason == DLL_PROCESS_DETACH) {
    return TRUE;

I played around with hs_exit instead of shutdownHaskell, I moved 
initialization and clean-up from DllMain to my library loader, nothing 
helps. Even doing no clean-up whatsoever does not change the behaviour.

Any ideas?

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