On 21 Jan 2014 at 10:09, Nat Goodspeed wrote:
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3747.pdf
That's a good paper, but I wish it didn't claim to be a *universal* model for asynchronous operations because that model is completely unsuitable for persistent storage i/o. I had that argument with Nicholas @ Microsoft Research actually, and I think I may well have persuaded him as they're seeing the same problems of fit.
Niall, would you be able to propose a more universal model? Please read this as a simple invitation rather than a challenge. The goal of the paper seems laudable: accepting an argument that allows the caller to specify whether to provide results with a callback, a future or suspend-and-resume.
I think I effectively have via AFIO which uses an asynchronous execution precedence graph model with explicit gathering for error propagation, which unlike the proposed model works as well with seekable i/o as fifo i/o. The problem with the AFIO model though is that it is very heavily reliant on the performance of futures (and therefore the memory allocator) as those are used to transport state between closures, and for those with very low latency very small packet (e.g. UDP) socket i/o it's unsuitable (which is of course pointed out in the WG21 paper). My opinion there is that callbacks can become a low level interface for those who need it, while the execution precedence graph model is much easier to program against for everything else. You're probably about to ask me for a N-paper, so I'll save an email cycle by explaining my hesitation on that. Bjorn Reece has been working extensively with me off list to de-wart AFIO when combined with ASIO such that async socket and async disc i/o seamlessly interoperate, specifically he's persuaded me to supply async_io_op to completion handlers which is going to be a technical challenge for me to implement in a safe and quick way, but I think I am capable though it's going to hurt. I will start that work item once I clear my maths coursework (hopefully tomorrow), and file my consulting company's annual accounts (hopefully end of this week). Also, I might actually have a job interview soon, which amazes me as I had expected at least three months to elapse before any jobs in C++ turned up (there are about six a year total in this region). Both Artur and Niklas who are leading out Microsoft's work on async in C++ are aware of AFIO's design approach, and last time I heard they found themselves coming ever closer to AFIO's design as they find blocking issues and corner cases in their proposals. I think it will be more productive for now for me to keep nagging them on their N-papers rather than write one of my own. After all, being in Europe and being unemployed makes it extremely tough to attend C++ standards meetings, and I don't personally rate a N paper's chances if someone isn't at the meetings to champion it i.e. present in the bar afterwards to argue merits with people. Hopefully this explains things. Do point out any problems in my thoughts. Niall -- Currently unemployed and looking for work in Ireland. Work Portfolio: http://careers.stackoverflow.com/nialldouglas/