- FFI - Haskell.org

Finalizers, again!
by Manuel M T Chakravarty 06 Mar '03

06 Mar '03

I have just read Hans Boehm's POPL paper on finalizers. His suggestion for the use of finalizers in single-threaded systems is to provide a `runFinalizers' routine, instead of relying on the asynchronous execution that, as established, requires support for concurrency. I am not sure whether we have given this option really serious consideration. Why may this option be interesting? It may allow us to have Haskell finalizers after all. As Boehm explains, ``finalizers generally fall into two categories: Those that simply deallocate operating system resources and those that touch other user data structures.'' It seems that we currently, probably due to our FFI bias, concentrate on the former kind. The main benefit of Haskell finalizers, apart from convenience, is the ability to process Haskell structures. As I understand Boehm, we might adopt the following design: * Finalizers are normal Haskell routines. * When the GC discovers that a finalizer becomes enabled, it is added into a list of enabled finalizers (but not run in a single-threaded system). * When the routine runFinalizers :: IO () is called, it runs the finalizers in the list of enabled finalizers one after the other. * Systems supporting pre-emptive concurrency *may* run finalizers at any time after they become enabled, but they must run them when `runFinalizers' is called (similar to `performGC'). An attractive property of this design is that it provides a smooth transition from single-threaded systems to systems providing pre-emptive concurrency. The requirement to invoke `runFinalizers' explicitly might not be too burdensome in practice as code making heavy use of the FFI and finalizers probably spends a lot of time in the IO monad with the opportunity to insert calls to `runFinalizers'. Opinions? Cheers, Manuel PS: Sorry for bringing finalizers up again, but if there is an opportunity to improve the current design, I think, we should consider it.

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Re: Comparing [Fun]Ptrs
by Sven Panne 06 Mar '03

06 Mar '03

Volker Stolz wrote: > [...] > class ToPtr a where > toPtr :: a -> Ptr b > [...] The problem with a class like this is that you can't define any sensible instances, apart from the trivial one for Ptr itself. There is no guarantee at all that e.g. a FunPtr, an Int, ... fits into a Ptr and there are actually platforms where this is not the case. It's perhaps OK as a hack, but it has no place in a general FFI library, Cheers, S.

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You missed my Birthday again!
by Ami 06 Mar '03

06 Mar '03

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[Fwd: Re: Foreign import]
by Gustavo Villavicencio 05 Mar '03

05 Mar '03

I have continued reading the bibliography on ffi but I cannot find the solution. Please, can anyone help me?. gustavo -------- Original Message -------- Subject: Re: Foreign import From: "Gustavo Villavicencio" <gustavov(a)ucse.edu.ar> Date: Tue, March 4, 2003 8:35 pm To: <chak(a)cse.unsw.edu.au> Thanks Manuel The error message is as follows -------------------------------------- CallIncr.o: In function `sWM_entry': CallIncr.o:(.text+0xc5): undefined reference to `incr' collect2: ld returned 1 exit status -------------------------------------- where 'incr' is a toy function defined in 'mylib.h'. Obviously, in the foreign declaration I have changed 'myfun' by 'incr'. The compilation command is the typical ghc -ffi -c CallIncr.hs followed by ghc -ffi CallIncr.o which generate the previous error. Thanks again, gustavo Manuel M T Chakravarty said: > "Gustavo Villavicencio" <gustavov(a)ucse.edu.ar> wrote, > >> I'm a new ffi user and I have some problems with foreign import >> declaration. I'm don't have any problem to access C standard >> functions. However, I cannot access to my own functions in mylib.h by >> means of >> >> foreign import "mylib.h myfun" hmyfun :: ... >> >> May be I'm omitting some compilation step or parameter also, since >> I'm applying the same compilation process to call C standard >> functions. >> >> I'm working with ghc 5.04 on SuSe Linux 7.0. > > You should say what goes wrong. Eg, paste the error > messages of the compiler and/or linker into your email. > > Manuel

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Comparing [Fun]Ptrs
by Volker Stolz 05 Mar '03

05 Mar '03

Hi, I'm looking for a way of comparing Ptrs to null *elegantly*. The FFI distinguishes between 'Ptr a' and 'FunPtr a', so testing would mean writing ((==) null[Fun]Ptr). This is rather tedious and a predicate 'isNull' might be in order so that it's possible to write when (isNull p) $ ... or throwIOErrorIf isNull ... , especially without having to worry about comparing against the correct null pointer (FunPtr or Ptr). That's something where a class can help, but I'm not sure whether such a specialised class is desired... I'd like to add the following class and instances/functions to Foreign.Ptr if nobody objects, they'd make code much more readable and concise: class ToPtr a where toPtr :: a -> Ptr b isNull :: ToPtr a => a -> Bool isNull = (==) nullPtr . toPtr The ToPtr class was suggested my Simon M. in favour of an even more specialised class PtrCmp which just has nullPtr :: PtrCmp a => isNull a -> Bool. -- Volker Stolz * http://www-i2.informatik.rwth-aachen.de/stolz/ * PGP * S/MIME

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Foreign import
by Gustavo Villavicencio 04 Mar '03

04 Mar '03

Hi, I'm a new ffi user and I have some problems with foreign import declaration. I'm don't have any problem to access C standard functions. However, I cannot access to my own functions in mylib.h by means of foreign import "mylib.h myfun" hmyfun :: ... May be I'm omitting some compilation step or parameter also, since I'm applying the same compilation process to call C standard functions. I'm working with ghc 5.04 on SuSe Linux 7.0. Any help will be welcome. gustavo

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need help with ffi function pointers
by David Sankel 02 Mar '03

02 Mar '03

Hello, I'm working on interfacing a c library that has the notion of callbacks. I have a C function: f_setCallback( void (funptr*) () ); I would like to allow a haskell developer to have an interface like the following: callback :: IO () callback = putStr "Called!\n" main :: IO () main = do setCallback callback -- etc. Is this possible via. ffi? If so, how would I do it code wise? Thanks, David J. Sankel

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Example: Binding C++ to Haskell using the ffi
by David Sankel 02 Mar '03

02 Mar '03

Here is some example code doing just that. It uses ghc. Questions: Can one think of better ways to interface generic c++ libraries to Haskell? What do you think of the ->> member function operator? for the ffi people: Has any though gone into cplusplus? If so, how would it interface? Would stubs on the c++ side be generated or would it use the code directly. Later, David J. Sankel

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by Erick Parker R. 02 Mar '03

02 Mar '03

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The best Cigar ever made, you must read this
by Karen Dever R. 01 Mar '03

01 Mar '03

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