[Haskell-iPhone] Automatically freeing function pointers

[Stephen Blackheath [to GHC-iPhone]]

David,

I hadn't quite grasped your code. The problem with your code is that 
these two lines...

 >                                     func <- funky
 >                                     freeHaskellFunPtr func

...allocate then deallocate a function pointer, with a net result of 
nothing useful, and no effect on the function pointer you allocated on 
the third line.

If you use this trick, however...

{-# LANGUAGE DoRec #-}

foreign import ccall safe "wrapper" mkInit
     :: (Ptr WorkerThread -> CInt -> IO ()) -> IO (FunPtr (Ptr 
WorkerThread -> CInt -> IO ()))

applicationMain init dealloc = mdo
     fInit <- mkInit $ \callbackWorker fd -> do
         freeHaskellFunPtr fInit
         ...
     ...

...then you can do it quite painlessly.  Note that DoRec is correct for 
ghc 6.10, but its name has changed in later ghc versions.  The compiler 
will tell you.


Steve

On 21/06/11 05:00, David Pollak wrote:
>
>
> On Sun, Jun 19, 2011 at 1:32 PM, Stephen Blackheath [to GHC-iPhone]
> <likeliest.complexions.stephen at blacksapphire.com
> <mailto:likeliest.complexions.stephen at blacksapphire.com>> wrote:
>
>     David,
>
>     In GHC-iPhone the number of function pointers that are allowed to be
>     active for a given function is limited, but you can change the size
>     of the limit.  This is documented in
>
>
> Steve,
>
> Yep... I understand that there are not an unlimited number of function
> pointers.  However, the function that I wrote was "supposed" to
> automatically release the function:
>
> runOnMain :: IO () -> IO ()
> runOnMain todo = do
>                    func <- funky
>                    dispatchFunc func
>    where funky =  mkStrCB $ \v -> do
>                                     todo
>                                     func <- funky
>                                     freeHaskellFunPtr func
>
> Note the freeHaskellFunPtr function call at the end of the lambda.
>
> I'm thinking that the "func <- funky" line is being treated as a
> recursive call and I'm also thinking that this is a limitation of my
> understanding the magic of lazy evaluation.
>
> So, please let me rephrase my question:
>
> How do I get the pointer to a wrapper function so that the pointer can
> be used within the wrapped function itself?
>
> I have worked around the particular issue by making a call to
> freeHaskellFunPtr in the Objective-C code that invokes the function.
> It's less optimal that being able to have the Haskell code be able to
> auto-free the function pointer after the function is invoked.
>
> Thanks,
>
> David
>
>     http://projects.haskell.org/__ghc-iphone/downloads/GHC-__iPhone.pdf
>     <http://projects.haskell.org/ghc-iphone/downloads/GHC-iPhone.pdf>
>
>     on p5 under 'Pool sizes for foreign function "wrapper" callbacks'.
>
>
>     Steve
>
>
>     On 18/06/11 11:29, David Pollak wrote:
>
>         Howdy,
>
>         I tried to build a function that would create an auto-freeing
>         function
>         pointer:
>
>         runOnMain :: IO () -> IO ()
>         runOnMain todo = do
>                            func <- funky
>                            dispatchFunc func
>            where funky =  mkStrCB $ \v -> do
>                                             todo
>                                             func <- funky
>                                             freeHaskellFunPtr func
>
>         Unfortunately, I wind up getting:
>           internal error: iPhoneCreateAdjustor - adjustor pool
>         'Main_d2K2' is
>         empty (capacity 32)
>              (GHC version 6.10.4-iphone-simulator for i386_apple_darwin)
>
>         I'm not sure why, but I suspect that funky is being called
>         recursively
>         and thus stuff is never being freed.
>
>         Any hints as to the issue and solutions?
>
>         Thanks,
>
>         David
>
>
>         --
>         Lift, the simply functional web framework http://liftweb.net
>         Simply Lift http://simply.liftweb.net
>         Follow me: http://twitter.com/dpp
>         Blog: http://goodstuff.im
>
>
>
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>
>
> --
> Lift, the simply functional web framework http://liftweb.net
> Simply Lift http://simply.liftweb.net
> Follow me: http://twitter.com/dpp
> Blog: http://goodstuff.im
>