December 2002 - Glasgow-haskell-users

RE: Native Threads in the RTS
by Simon Peyton-Jones 01 Dec '02

01 Dec '02

Improving. Want to put it in CVS? Simon M can suggest where. Simon | Definitions | ~~~~~~~~~~~ | A native thread (aka OS thread) is a thread as defined by the operating | system. | A Haskell thread is [*** FIXME - How shall I put this? ***] the thing | you see from Haskell land. A "Haskell thread" encapsulates the execution of a Haskell I/O action. A Haskell thread is created by forkIO, and dies when the I/O action completes. A Haskell thread is always executed by a native thread. The Haskell RTS creates one or more "worker native threads" to execute Haskell threads. | Haskell threads may be associated at thread creation time with either | zero or one native threads. Each Native thread is associated with zero | or more native threads. zero or more *Haskell* threads. Can you give an example of when a native thread is associated with more than one Haskell thread? To avoid "A Haskell thread associated with a native thread" I'd prefer to define the term "a bound Haskell thread". I would also like to describe a "bound native thread" as one that has associated Haskell thread(s). | If a native thread is associated with one or more Haskell threads, | exactly one of the following must be true: | *) Exactly one Haskell thread associated with the native thread is | executing. | *) The native thread is executing foreign code. | *) The native thread and all Haskell threads associated with it are | blocked. You don't say (but you do mean) A bound Haskell thread can be executed only by its associated native thread You don't say (and I'm not sure if you mean) If a bound native thread blocks, all of its associated Haskell threads are blocked too If a bound Haskell thread blocks, its associate native thread and all its associated Haskell threads also block. | The thread that main runs in, threads created using forkIO and threads | created for running finalizers or signal handlers are not necessarily | associated with a native thread. However, an implementation might | choose to do so. But the impl may *not* choose a bound native thread. These must be kept inviolate. | When a "free" foreign exported function is invoked, the implementation | may freely choose what kind of Haskell thread the function is executed | in. It is not specified whether this thread is associated with a | particular OS thread or not. Again, it must not be a bound native thread. | When a foreign imported function is invoked [by Haskell code], the | foreign code is executed in the native thread associated with the | current Haskell thread, if an association exists. If the current | Haskell thread is not associated to a native thread, the implementation | may freely decide which thread to run the foreign function in. | The existing distinction between unsafe, safe and threadsafe calls | remains unchanged. If a bound Haskell thread calls a foreign import that is not labelled 'threadsafe' which calls a bound foreign export does that work? What if the foreign export was not bound? Similarly, if the foreign import was labelled 'threadsafe', would it work? It's not obvious to me. Some kind of semantics would be good.

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RE: Request: suppress specific warnings at specific places
by Simon Marlow 01 Dec '02

01 Dec '02

> GHC's excellent warnings are very helpful. They would be somewhat > more so if it were possible to suppress a warning about a specific bit > of code. One possible syntax (to which I gave no commitment) would be > > {-# WOFF "non-exhaustive pattern matches" #-} > <offending code> > {-# WON "non-exhaustive pattern matches" #-} > > . Another would be > > {-# WOFF 523 #-} > <offending code> > {-# WON 523 #-} > > where 523 is a warning number emitted with the warning message. > > This would be particularly useful with the recently granted wish for > -Werror. This would be nice, but it would be tricky to implement: declarations have to be tagged with a list of "exceptions" to the prevailing warning settings. I doubt we'll do this any time soon, but patches are welcome as usual... (of course, the workaround is to put the offending code into a module of its own, and use OPTIONS to turn off the appropriate warnings). Cheers, SImon

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5.04.1 on OS X
by Nicolas.Oury 01 Dec '02

01 Dec '02

Hello, is there a binary distribution for Mac OS x of GHC 5.04.1? Best regards, Nicolas Oury

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Calling haskell DLL from MSVC++
by Mauricio Carvalho 01 Dec '02

01 Dec '02

Hey! I' having problems to call functions from a DLL made with ghc with a C++ program, using Microsofts Visual C++ To learn how to do it, I tried the example found at the user's guide (11.3, 11.4), but things aren't working out.. Here is as far as I've done: I have a haskell module, MyModule.hs:module MyModule where foreign export stdcall fac :: Int -> Int fac :: Int -> Int fac n | n <= 0 = 1 | otherwise = n * fac(n-1) I compile it with: ghc -c MyModule.hs -fffi The .c file, containing the DLL initialization is: #include <windows.h> #include <Rts.h> extern void __stginit_MyModule(void); static char *args[] = {"MyDll", NULL}; BOOL STDCALL DllMain(HANDLE hModule, DWORD reason, void *reserved){ int i; if(reason == DLL_PROCESS_ATTACH){ printf("\nStarting Haskell"); startupHaskell(1, args, __stginit_MyModule); printf("Haskell Started!!"); return TRUE; } return TRUE; } Which I compile with: ghc -c MyDll.c I build the DLL with: ghc --mk-dll -o MyDll.dll MyModule.o MyModule_stub.o MyDll.o The DLL is build, and following the example, I try to call it from VB, but the program hangs. I don't know if I'm missing something in the building process, I can't see what it can be. Moreover, for calling it from my C++ programs, I need a library file (generally called .lib in MSVC linker, I think it's equivalent to the libMyLib.a of gcc) to resolve the function (fac) when linking. I tried to use dlltool -b MyDll.dll -l MyDll.lib to contruct the .lib file, it's contructed, but yet, when I use to link my C++ program with the DLL, i got unresolved external symbol for the function. Thus, I can't even link the C++ program. Note that I used the stdcall (for fac)to follow the example; I tried even with ccall, but without success either. Can someone see if I'm missing something at the creation process of the dll? And to create the library file, is it the right thing to do? Mauricio

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