Re: [Haskell-cafe] FFI nested structs - malloc - free

Hi! Disclaimer: I haven't worked much with FFI, so I'd like someone confirmed my words. Seems that allocated memory in your example is supposed to be freed from inside C. It's not a memory leak. If I understand correctly documentation [1], malloc/free are just a simple wrappers around C's malloc/free. It's mallocForeignPtr that sets finalizer. Best regards, Alexey Shmalko [1]: https://downloads.haskell.org/~ghc/7.8.3/docs/html/users_guide/ffi-ghc.html On Tue, May 5, 2015 at 6:45 AM, Proclivis wrote:

I should have mentioned GHC 7.8.3 Ubuntu 64bit

Sent from my iPad

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On May 4, 2015, at 9:42 PM, Proclivis wrote:

FFI Gurus,

I created a c2hs FFI of a nested C structure, where struct A has a pointer to a struct B. To do so, I used a malloc, but I am unsure if the memory will be freed when the resulting Ptr is freed.

The example at this link uses the same technique, so it will serve as an example.

https://github.com/ifesdjeen/haskell-ffi-tutorial/blob/master/src/Example.hs...

Line 48 and 51 do the malloc and assign the pointer in the struct, from inside a Storable poke implementation.

But, there is no explicit free, nor a finalizer.

Will the memory be freed when the Ptr of the Storable is freed?

If it is, it implies that some magic keeps track of mallocs inside a poke, and creates finalizers. Or, this example leaks. If it leaks, how do I create a finalizer from inside a poke implementation?

Mike

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