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@blacksapphire.com

<mailto:likeliest.complexions.stephen@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


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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