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Subject: Re: [boost] [next gen future-promise] What to call the monadic return type?
From: Hartmut Kaiser (hartmut.kaiser_at_[hidden])
Date: 2015-05-28 18:11:31

> > Optimizing away one allocation to create a promise/future pair (or just
> a
> > future for make_ready_future) will have no measurable impact in the
> context
> > of any I/O, be it wait free or asynchronous or both.
> No one here is claiming better futures make any effect on i/o
> performance except you.

>From the AFIO docs:

AFIO is 'A C++ library which lets you schedule an ordered dependency graph
of file input/output operations...'
( And
you said more than once that a) the new 'futures' are 'much' faster and b)
that you want to use those for AFIO. Go figure.

You have mentioned wait free algorithms in the ext4 file system caches which
would make file system IO so fast that using your 'futures' would be
beneficial (see your mail: You
even mention it further down in the mail Iäm answering to. Go figure.

Others have drawn direct connections on this thread between futures and IO
as well (see for instance Gavin Lambert:, or
Avi Kivity: Go

You clearly should decide what you want besides trolling the Boost-devel
mailing list.

> You are reading only the parts of the thread
> you want to in order to believe what you already believe (apparently
> that I have some master plan of "taking over" Boost).

I have not said or implied anything like that in this thread. Also, you know
best what your 'master plan' is.

> You drew the
> link here between i/o and futures, none of us claimed it. The thread
> earlier was clearly about two entirely separate topics. You conflated
> them to make your own personal point.

I have not conflated anything.

> > In general, all I'm hearing on this thread is 'it could be helpful', 'it
> > should be faster', 'it can be important', or 'makes a big difference',
> etc.
> > I was hoping that we as a Boost community can do better!
> Constant cherry picking of thread topics just to nay say and put down
> any discussion of alternative idioms and designs isn't being positive
> nor helpful.

Constant? Really? Just because I believe that your ideas have flaws and your
solutions are wrong because you start from incorrect assumptions?

> > Nobody so far has shown the impact of this optimization technique on a
> real
> > world applications (measurements). Or at least, measurement results from
> > artificial benchmarks under heavy concurrency conditions (using decent
> > multi-threaded allocators like jemalloc or tcmalloc). I'd venture to say
> > that there will be no measurable speedup (unless proven otherwise).
> Again nobody claimed that. I was quite clear I primarily want single
> op code reduction as part of unit testing. That's its main purpose
> for me as a per-commit CI test that I am writing perfectly optimal
> code, not just mostly optimal code.

What is 'op code reduction' all about if not to achieve speedup? All I asked
is to give us numbers showing whether those 'op code reductions' have any
_significant_ impact on the overall performance of real world applications.
All you gave us so far are conjectures.

> A happy consequence is a
> potential runtime cost optimal monadic transport, and that's what I
> came here to bikeshed a name for, and see if there is interest in
> such a development. Feedback on both has been both positive, and
> useful, so I will proceed.

Sure. I'm off of this thread. Happy bikeshed-ing!

Regards Hartmut

> I have also been very clear that this new design solves my major
> problems, not *the* major problems with existing futures. That's what
> I designed it to do. I believe it also solves the same problems as
> face futures in ASIO. Once finished and deployed, if others find it
> solves their problems too then it has a great chance on becoming a
> next gen Boost future. If it doesn't, then it won't.
> I have been working on this replacement future design since October,
> with multiple presentations of my code experiments here to gain
> feedback. Others have presented their code experiments here too. We
> have all reviewed each other's design ideas and code, and evolved our
> own designs and code in response. If this exchange of code
> experiments between people all with similar problems with existing
> futures isn't what Boost is exactly all about, then I don't know what
> negative and cynical vision of Boost you have. Multiple people here
> have problems with futures, and multiple people are experimenting
> with improvements. This is something that should be welcomed, not
> constantly put down with negativity.
> I would expect you'll see me present benchmarks here in due course
> once the implementation is drop in replaceable. I am expecting about
> a 5% performance improvement in AFIO as a drop in, and a 20%
> improvement once I replace AFIO's continuations infrastructure with
> .then() and remove the central spinlocked unordered_map. This should
> help further close the gap between AFIO and ASIO which is currently
> between 15% and 32%. That gain is what I am developing these futures
> for after all - to solve my problems, and maybe as a happy
> consequence solve other people's problems too.
> Niall
> --
> ned Productions Limited Consulting

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