Free pointers in parser activations

[adrianeboyd]

Description

Free the remaining pointers in the ActivationsC activations at the end of _parseC() in Parser.

This is the only definite spacy-related memory leak I found with valgrind using examples from #3618. (I think there may be some remaining issues related to cython/numpy.)

Types of change

Bugfix.

Checklist

• I have submitted the spaCy Contributor Agreement.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[honnibal]

Oh awesome! Nice work. Would you consider writing up a tutorial on how to use Valgrind on a Cython project? As I mentioned in Slack, I've always wanted to use it but have had trouble getting started.

I feel sheepish about this memory leak, as it could have been discovered the old-fashioned way by just grepping for malloc and calloc. I normally try to be careful when I'm using them, because they break the normal pattern of cymem.Pool and take some vigilance. I'm not sure why I messed this up.

[adrianeboyd]

I only kinda sorta know what I'm doing, but I can sketch out the basics of how I did this, sure!

[honnibal]

Ah, I think I see how I missed this. The allocations and the frees are happening in different modules, which makes the mistake much more likely.

I suggest we make it a bit easier to see that the _parseC loop owns that memory. The smallest change would be to just call spacy.syntax._parser_model.resize_activations() at the start of the loop. Probably better is to add some setup and teardown functions to _parser_model.pyx:

cdef ActivationsC alloc_activations(int n_states) nogil:
    cdef ActivationsC acts
    memset(&acts, 0, sizeof(acts))
    resize_activations(&acts, n_states)
    return acts

cdef void free_activations(const ActivationsC* acts) nogil:
    free(acts.token_ids)
    free(acts.scores)
    free(acts.unmaxed)
    free(acts.hiddens)
    free(acts.is_valid)

We would then remove the resize_activations function from the _parser_model.pxd, as the allocations should be private to the module.

[adrianeboyd]

However you think is best...