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

[Alexey Shmalko]

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 <mike at proclivis.com> wrote:
> I should have mentioned GHC 7.8.3 Ubuntu 64bit
>
> Sent from my iPad
>
>> On May 4, 2015, at 9:42 PM, Proclivis <mike at proclivis.com> 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.hsc
>>
>> 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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