- FFI - Haskell.org

Bom dia ffi
by Marta 29 Jun '03

29 Jun '03

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ANI TOUR YAZ-2003 Katalogu
by ANI TOUR 29 Jun '03

29 Jun '03

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RE: exercising the storage manager
by Simon Marlow 10 Jun '03

10 Jun '03

> g'day everyone, > > I'm getting segv's from a program using the FFI (ghc5.0x) on > MacOS X only, > i.e. not on Linux, my primary development platform. > > So... does anyone have any tips for showing up dodgy uses of > the FFI wrt > memory handling? What settings for GHC's garbage collector > will create the > most pathological situations? > > Also, I have some qualms about foreignPtrToPtr; by it's type, > it seems to > be exactly what you want most of the time, but due to the "if > this is the > last reference, the finalizers may run" caveat it almost always isn't. > I note that it already has some warnings attached to it, but... Most of the time you should be using 'withForeignPtr'. I don't think there can be any legitimate uses for foreignPtrToPtr unless there is a touchForeignPtr that is guaranteed to happen later. And that's a tricky guarantee, because it involves reasoning about strictness. Does anyone else think that foreignPtrToPtr should really be called unsafeForeignPtrToPtr? > - does anyone have a safe use for it that doesn't involve > touchForeignPtr? > > - can the FFI spec somehow group together all functions that > may introduce memory leaks or unsafety? Unsafety is normally indicated with an 'unsafe' prefix on the function name. Memory leaks are a different matter - since malloc on its own can introduce a memory leak, I'm not sure how you'd indicate that. Cheers, Simon

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Bom dia ffi
by kandrak 10 Jun '03

10 Jun '03

Message to ffi(a)haskell.org Ola!!!! ffi GANHAMOS O PRÊMIO DE MELHOR SITE DO RAMO ======Estamos operando em Novo Formato====== Confira em: escuta21.kit.net ou http://www.escuta21.kit.net ei.... ffi Cuidado com o que fala ao Celular... ele tb tem ouvidos... para remover o ffi(a)haskell.org de nossa lista responda este e-mail e coloque remover nos perdoe o transtorno...ok? kandrak

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exercising the storage manager
by Peter Gammie 10 Jun '03

10 Jun '03

g'day everyone, I'm getting segv's from a program using the FFI (ghc5.0x) on MacOS X only, i.e. not on Linux, my primary development platform. So... does anyone have any tips for showing up dodgy uses of the FFI wrt memory handling? What settings for GHC's garbage collector will create the most pathological situations? Also, I have some qualms about foreignPtrToPtr; by it's type, it seems to be exactly what you want most of the time, but due to the "if this is the last reference, the finalizers may run" caveat it almost always isn't. I note that it already has some warnings attached to it, but... - does anyone have a safe use for it that doesn't involve touchForeignPtr? - can the FFI spec somehow group together all functions that may introduce memory leaks or unsafety? cheers peter

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ANN: H98 FFI Addendum 1.0, Release Candidate 9
by Manuel M T Chakravarty 10 Jun '03

10 Jun '03

RC 9 of the FFI Addendum is now at http://www.cse.unsw.edu.au/~chak/haskell/ffi/ The addendum seems to be stable and I like to close Version 1.0. There is only one open question: What to do about "threadsafe"? In the threads discussion, there seemed to be a tendency to not distinguish between "threadsafe" and "safe" after all. Shall we remove "threadsafe" from 1.0? That's what I tend to and will do unless there are strong arguments to retain "threadsafe". Cheers, Manuel -=- Changes since RC 8 * 5.8: `MarshallAlloc.reallocBytes' is no longer permitted on memory allocated with `alloca' or `allocaBytes'. * 6.1: Deinitialisation of the RTS via `hs_exit()' followed by (re)initialisation with `hs_init()' must be supported.

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RE: FFI Help
by Simon Peyton-Jones 09 Jun '03

09 Jun '03

Manuel Would it be worth mentioning or amplifying this point in the FFI spec, or perhaps in an accompanying Appendix/Commentary of examples and FAQs? Else someone else is going to trip over it sooner rather than later. Simon | -----Original Message----- | From: haskell-cafe-admin(a)haskell.org [mailto:haskell-cafe-admin@haskell.org] On Behalf Of Glynn | Clements | Sent: 04 June 2003 08:32 | To: Matthew Donadio | Cc: haskell-cafe(a)haskell.org | Subject: Re: FFI Help | | | Matthew Donadio wrote: | | > I am just starting to experiment with FFI, and am running into a | > problem. I was to create an FFI to the lgamma(3) found in many of the | > newer libm implementations. My code follows the sig. | > | > The lgamma function works. The gamma function core dumps (I am using | > ghc 5.04.3) on me. gdb reports a SIGSEGV in signgam(), but I'm not sure | > why. I believe that I need to use the monad because signgam is only | > valid after lgamma returns. | > | > Does anyone have an idea what I am doing wrong? | > | > Thanks. | > | > -- | > Matthew Donadio <m.p.donadio(a)ieee.org> | > | > > module Gamma (gamma, lgamma) where | > | > > import System.IO.Unsafe | > | > > foreign import ccall "math.h lgamma" lgammaC :: Double -> IO Double | > > foreign import ccall "math.h signgam" signgamC :: IO Int | | signgam is an "int" variable, but this assumes that it is a function | of type "int signgam(void)". | | Write a C wrapper "int get_signgam(void) { return signgam; }" and | import that. | | -- | Glynn Clements <glynn.clements(a)virgin.net> | Or alternatively, foreign import the address of the int and read it | directly with 'peek'. | | import Foreign | ... | foreign import ccall "math.h &signgam" signgamC :: Ptr Int32 | ... | gammaIO :: Double -> IO Double | gammaIO x = do lg <- lgammaC x | s <- peek signgamC | return $ fromIntegral s * exp lg | | | Regards, | Malcolm

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RE: ANN: H98 FFI Addendum 1.0, Release Candidate 10
by Simon Marlow 08 Jun '03

08 Jun '03

> We routinely use code like this: > > data Point > foreign import getMousePos :: Ptr Point -> IO () > foreign import getX :: Ptr Point -> IO Int > foreign import getY :: Ptr Point -> IO Int > > The idea being that: > > 1) there is a foreign type (which might be called Point, > MousePos, point_t, struct point or whatever) > > 2) that we have a pointer to it > > 3) that the thing we have a pointer to can take on a number > of different > values. We don't know what the values are but this doesn't > mean they don't exist. Let's be clear about the role of Point here: it is a dummy type argument to Ptr, used to disambiguate the type 'Ptr Point' from any other kind of Ptr. It is for type-safety in the Haskell code. Additionally, the type argument to Ptr is used to resolve overloading when doing marshalling using the Storable class, but we're not using that facility here because no marshalling is going on. There definitely aren't any values of type Point, so I don't see why it needs a semantics. The semantics of empty data declarations seems like an entirely orthogonal issue, and I don't see any problem with the current semantics for empty data declarations, which is a completely natural degenerate case of ordinary data declarations. > > And what do you mean by a trick? > > It is possible that, since we cannot directly observe values > of foreign types, > we can safely model the type as having just one value > (bottom) or, perhaps > even no values at all. By this I mean that exactly the same > properties can > be proved whether we use an accurate model or a simplified model. > > But, it is a trick because we know that there is not just one > (or zero) values in that type (at least, for most types). I don't agree with that last sentence: there's no trickery going on; it doesn't matter how many values of the type Point there are. I could use any Haskell type with the same results. Let me say this another way: the type argument to Ptr in no way represents the type of the foreign data. It is used to resolve overloading and to disciminate pointer types in Haskell marshalling code, that's all. There is no link between the semantics of the Haskell type and the semantics of the foreign type (whatever that might be), and we shouldn't confuse the issue by pretending that there is. Cheers, Simon

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RE: How to access defines and enums in a convenient way?
by Simon Marlow 06 Jun '03

06 Jun '03

> I am doing some wrappers for c functions, and I need to > access defines, enums, and structs. > > I am doing this by writing access functions in c, so that I can call > them from Haskell. > > Is there a way to write this c code inline in the Haskell > module? You want to use a tool to make all this easier. There are various tools available: green-card, c2hs, and hsc2hs are the most commonly-used ones these days. Alastair Reid wrote a good comparison of the various tools (can't remember the link off hand though). There are examples of hsc2hs code in the libraries - particularly fptools/libraries/unix has examples of doing defines, enums and structs. Examples of green-card stuff can be found in fptools/libraries/HGL and fptools/libraries/X11. Take a look at Manuel's GtkHS for c2hs examples. Cheers, Simon

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How to access defines and enums in a convenient way?
by Martin Norbäck 06 Jun '03

06 Jun '03

I am doing some wrappers for c functions, and I need to access defines, enums, and structs. I am doing this by writing access functions in c, so that I can call them from Haskell. Is there a way to write this c code inline in the Haskell module? Since any implementation of FFI must do this via C anyway (to access the header files), it could simply inline the code as well. It's a bit of a bother to have to specify the object files for the access functions when compiling a Haskell program, especially since I am writing library modules and the program using the library shouldn't need to bother with extra object files. Regards, Martin -- Martin Norbäck d95mback(a)dtek.chalmers.se Kapplandsgatan 40 +46 (0)708 26 33 60 S-414 78 GÖTEBORG http://www.dtek.chalmers.se/~d95mback/ SWEDEN OpenPGP ID: 3FA8580B

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