Re: [PATCH v2 25/27] attr: store attribute stack in attr_check structure

From: Junio C Hamano <gitster@pobox.com>
Date: Jan 24, 2017, 02:28 UTC
Message-ID: <xmqqinp5p4x2.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20170124011135.GB187696@google.com>

Brandon Williams <bmwill@google.com> writes:

> ... It seems like breaking the question and answer up
> doesn't buy you much in terms of reducing allocation churn and instead
> complicates the API with needing to keep track of two structures instead
> of a one.

In my mind, the value of having a constant check_attr is primarily that it gives us a stable pointer to serve as a hashmap key, i.e. the identifier for each call site, in a later iteration.

Of course, in order to populate the "question" array, we'd need the interning of attribute names to attr objects, which need to be protected by mutex, and you would probably not want to do that every time the control hits the codepath.

But all of the above comes from my intuition, and I'll very much welcome to be proven wrong with an alternative design, or better yet, a working code based on an alternative design ;-).