Stefan Beller <sbeller@xxxxxxxxxx> writes: > On Wed, Oct 12, 2016 at 2:38 PM, Junio C Hamano <gitster@xxxxxxxxx> wrote: >> Johannes Sixt <j6t@xxxxxxxx> writes: >> >>> 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 >> <xmqqeg3m8y6y.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxx>, 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.