ef_ race condition

[SeanU]

There seems to be a race condition around the ef_ search parameter. If I've got two threads running searches concurrently, it's possible that thread A could try to set it to one value, and then have thread B change it to something else before it is able to execute the search.

I'd like to resolve it by adding an ef parameter to searchKnn:

std::priority_queue<std::pair<dist_t, labeltype >> searchKnn(void *query_data, size_t k, size_t ef);

and then adding an overload that has the current signature, and just passes the current value of ef_ in. This would mostly preserve the current behavior for existing code, while adding the option to override that setting for individual searches.

There would be some minor behavior change as a result of reducing the size of the window for that race condition. I assume that would be acceptable?

[yurymalkov]

@SeanU, thank you for the suggestion!
Sounds great. Can you make a pool request?

[SeanU]

Yeah, absolutely. I’ll try to get it done this weekend.