Re: [PATCHv2] attr: convert to new threadsafe API

Stefan Beller [off-list ref] writes:

On Wed, Oct 12, 2016 at 2:38 PM, Junio C Hamano [off-list ref] wrote:

quoted

Johannes Sixt [off-list ref] writes:

quoted

Sigh. DCLP, the Double Checked Locking Pattern. ...
I suggest you go without it, then measure, and only *then* optimize if
it is a bottleneck.

That comes from me in earlier discussion before the patch, namely in
[ref], where I wondered if
a cheap check outside the lock may be a possible optimization
opportunity, as this is a classic singleton that will not be
deinitialized, and once the codepath gets exercised, we would be
taking the "nothing to do" route 100% of the time.

Having followed that advice (and internally having a DCLP), I think
we have Triple Checked Locking Pattern in this patch.  Nobody wrote
a paper on how that would not work, yet. ;)

In the reroll I plan to reduce it to a Single Checked (inside a mutex)
Locking Pattern, though I would expect that performance (or lack thereof)
will show then. But let's postpone measuring until we have a working patch.

Oh, that wasn't even an "advice" (read it again).  I fully agree
that starting simple would be the way to go.