On 29/01/12 15:57, David Matthews wrote:
On 27/01/2012 20:15, Phil Clayton wrote:
Thinking about explicitly deleting callbacks led me to ask whether each ML function passed as a callback has its callback reused on subsequent calls. If reuse occurs, the number of call sites in the source code would bound memory usage.
I'm guessing that these callback objects are actually wrappers to invoke compiled ML code and that there is only one instance of the compiled ML, so there would be no problem having only one instance of the callback object.
It would be nice if they could be reused but currently they aren't. I had a look at the code and did some experiments but the problem is that there is quite a lot of ML wrapping going on. That means that the RTS can't detect that the same function has been passed a second time. After the wrapping has been applied the closure that gets passed into the RTS is always different even if the same ML function was used further up.
I sometimes think the whole FFI system should be redesigned to remove some of the layers.
Thanks for investigating. It looks like every callback is leaking something like 0x38 bytes of memory which isn't an issue in the short term while I am only developing prototype GTK applications. (An application would need to run for days, if not weeks, for this to cause problems.)
I suspect that it would be possible to call an explicit delete from C on the callback pointer when no longer required. Is that the sort of mechanism you envisaged for deleting callbacks? However, I am happy if you want to hold off any solution as the issue is not a show-stopper.
Phil