On Thu, Jan 4, 2018 at 3:18 PM, Nathaniel Smith <njs at pobox.com> wrote: > I think the fix is a little bit cumbersome, but straightforward, and > actually *simplifies* caching. [...] > And then the caching in get() becomes: > > def get(self): > if tstate->current_context != self->last_context: > # Update cache > self->last_value = tstate->current_context_data->hamt_lookup(self) > self->last_context = tstate->current_context > return self->last_value Actually, this trick of using the Context* as the cache validation key doesn't work :-/. The problem is that the cache doesn't hold a strong reference to the Context, so there's an ABA problem [1] if the Context is deallocated, and then later the same memory location gets used for a new Context object. It could be fixed by using weakref callbacks, but that's not really simpler than the current counter-based cache validation logic. -n [1] https://en.wikipedia.org/wiki/ABA_problem -- Nathaniel J. Smith -- https://vorpus.org
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