On 9 Sep 2014 at 15:03, Rodrigo Madera wrote:

Looks very interesting and I would love to see that lib happen.

I believe in building up on knowledge recursively. So the first thing I would do is read on the enormous effort ZeroMQ [1] has put into analysing this problem domain. They have a (very) large set of material debating and explaining design decisions made on the library. After that, there is nanomsg [2], which is a derivative work from the lessons learned from ZeroMQ itself. Have you read through those in search of insights? It would be a very good source of debate material for this brand new library. There are problems they have encountered already, though you may decide to solve them differently.

Yes, we did. And therein lies the debate: ASIO's design was a product of its time, and while its design was close to optimal for its time, it now makes life harder than it should be in a world with 40Gbit ethernet, mobile devices where power consumption is important, and where non-Linux operating system kernels can DMA straight to and from user space if and only if you are very careful with how you use ASIO. The debate lies in to what extent does one break with ASIO's established norms and practices to achieve the features I listed. Even deciding on how much C++ 14 to use, or how much to embrace C++ 17 resumable functions is controversial.

Of course, that is if you haven't read that already. It just reminded me of how many insights these guys had in all the years they spent using and creating network middleware code. And basing a new network library off of this knowledge could be good.

I would strongly emphasise that no one is proposing we try doing ZeroMQ or anything like it "better". In our reliable messaging library we would provide the absolute minimum abstraction with which one could build *any* reliable messaging solution of their choice. The contract does involve the replication of at least one reliable UDP implementation (actually one of Chris' early implementations) as the original has heavily bitrotted, but apart from that we were thinking of UDT as a second backend, and leaving it at that. We chose UDT mainly because we believe we can reuse some of it for duplicating Chris' RUDP implementation.

About the language, I would totally look forward into C++11 and up design.

Be aware that C++ 11, and especially C++ 17 as it currently is thought to become, consider future-promise as the sole way for i/o completion handlers to be invoked via the new future<T>.then(callable) function. In particular, 17's resumable function support *requires* that the function must return a future, so if you want language based coroutine support, you must use future<T>. As much as Chris and many ASIO users are opposed to that design choice, we must play with the hand we have been dealt by WG21. I will say that future-promise can be made constexpr and no-alloc, and that makes an awful lot of the inefficiency go away, though an implicit synchronisation is unavoidable as .then() must check if the operation has already completed. On 9 Sep 2014 at 21:31, Andrew Marlow wrote:

Is it going to include reliable multicast? If so then a good place to start is the RFCs and various attempts at reliable multicast in the past. The two that spring to mind are NORM ( http://downloads.pf.itd.nrl.navy.mil/docs/norm/NormDeveloperGuide.html) for which there is a reference implementation, and PGM (Pragmatic General Multicast, http://tools.ietf.org/html/rfc3208). Don't forget Scalable Reliable Multicast, SRM, http://en.wikipedia.org/wiki/Scalable_Reliable_Multicast. There are whole frameworks based just on reliable multicast, e.g. spread, http://www.spread.org. Personally, I think this is far too big an area for boost. $0.02.

We are very much thinking of an abstraction framework with which one could implement things like the above. The hope would be that our new library would take care of platform-specific hassle like making whole system zero-copy networking right to and from the NIC disappear, stuff like that. We are also considering a monadic continuations framework allowing code just above ASIO to use ASIO generically. In other words, the standard C++ i/o monad equals ASIO. This ought to very significantly ease the writing of highly generic code avoiding much of the boilerplate you often need to join up ASIO async handlers, and therefore should make much easier implementing ZeroMQ or reliable multicast or any other messaging protocol. Another debate is indeed where the bottom level wire protocol should end and the monadic high level part should begin. For example some feel this approach would make impossible the reuse of third party implementation libraries. Niall -- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/

On 10 Sep 2014 at 20:09, Vicente J. Botet Escriba wrote:

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Be aware that C++ 11, and especially C++ 17 as it currently is thought to become, consider future-promise as the sole way for i/o completion handlers to be invoked via the new future<T>.then(callable) function. In particular, 17's resumable function support *requires* that the function must return a future, so if you want language based coroutine support, you must use future<T>. Niall, C++17 is not done. There is a paper generalizing resumable functions, so that they can return other types than future<T>. This is very interesting, as it could be used also for expected. The promise/future you are working on could be used also :)

Ah, my hope would be that the expected based future becomes the standard future. It would be enormously more efficient if we can avoid the memory allocator, if not the cmpxchg instruction. That said Vicente, right now I am trying to port expected to VS14 CTP 3. Oh the joys of internal compiler errors!

...

As much as Chris and many ASIO users are opposed to that design choice, we must play with the hand we have been dealt by WG21. I will say that future-promise can be made constexpr and no-alloc, and that makes an awful lot of the inefficiency go away, though an implicit synchronisation is unavoidable as .then() must check if the operation has already completed. Again nothing is fixed. Things evolve, and we don't know yet what the next concurrency TS will contain.

Very true. My statements were made in case though focusing on ASIO were not fully aware of what I meant by a C++ 14 based approach i.e. quite some change over current practice. I have been ruminating with Louis Dionne about how best to model an asynchronous i/o monad using expected. It is proving mind hurty. Niall -- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/

On Thu, Sep 11, 2014 at 1:51 PM, Niall Douglas wrote:

On 10 Sep 2014 at 23:12, Andrey Semashev wrote:

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How would it compare to SCTP and why not just add support for SCTP

to

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Boost.ASIO?

It wouldn't compare to SCTP. It would make the adding of SCTP support to ASIO much easier hopefully.

On 11 Sep 2014 at 9:26, Václav Zeman wrote:

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+1. I have had the same thought.

For my client's purposes, SCTP is not useful because it is not TCP nor UDP, and therefore is not understood by home networking equipment. This is a showstopper for them. There is SCTP over UDP, however there is no mature portable implementation library for that which I am aware of. In comparison, UDT is portable and has a mature portable implementation library, and one in fairly high quality C++ at that too. Hence the choice of UDT over SCTP as the second wire format we are likely to implement.

There is libusrsctp [1][2], although it's under BSD license (as is the UDT library) and in C. UDT over SCTP looks like a duplicate work since the functionality of these protocols largely overlap (as far as I can see from Wikipedia). Basically, that's why SCTP looks so appealing - it offers everything UDT does and then some, and it is standardized. [1] http://sctp.fh-muenster.de/sctp-user-land-stack.html [2] https://code.google.com/p/sctp-refimpl/source/browse/trunk/KERN/usrsctp/

On Thu, Sep 11, 2014 at 4:14 PM, Niall Douglas wrote:

On 11 Sep 2014 at 15:10, Andrey Semashev wrote:

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...

Hence the choice of UDT over SCTP as the second wire format we are likely to implement.

UDT over SCTP looks like a duplicate work since the functionality of these protocols largely overlap (as far as I can see from Wikipedia). Basically, that's why SCTP looks so appealing - it offers everything UDT does and then some, and it is standardized.

I think you thought I said we intend to implement UDT atop of SCTP. SCTP isn't useful to us due to the lack of home networking equipment support, we won't be implementing that.

Oh, sorry, I misread your previous reply.

On 10.9.2014 21:12, Andrey Semashev wrote:

On Tuesday 09 September 2014 17:59:12 Niall Douglas wrote:

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Dear Boost and ASIO users,

CC: boost@lists.boost.org, asio-users@lists.sourceforge.net

I am writing to ask for comments on the design of and interest in a generic reliable messaging library based on ASIO.

How would it compare to SCTP and why not just add support for SCTP to Boost.ASIO?

+1. I have had the same thought. -- VZ

On 12 Sep 2014 at 13:05, Bjorn Reese wrote:

Regarding libusrsctp, I looked into that recently, but it requires changes to the library and API to be integrated with Asio, or any other third-party main-loop for that matter (and I do not feel comfortable about its prevalent use of global variables and #ifdef's.)

Also my assessment of libusrsctp. UDT v4.0's source code is much cleaner. A long term dream of mine is for ASIO to become the standard event dispatch loop for all C++ programs, so other libraries simply hook into ASIO's dispatch and everything interoperates cleanly without lots of hassle and brittle boilerplate. I also feel a grievance against every single library firing up their own thread pools or worker threads when ASIO gives you that for free. Niall -- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/

On Thursday 11 September 2014 09:50:16 adzm wrote:

For example, over the years I've coded several UDP hole punch implementations, and have always wanted to submit them to boost, but they ended up depending on some non-standard functionality for things like authentication, match-making, IP address detection, etc. The alternative leads to something like ICE, but the complexity level rises quickly after that.

I think an ICE library (which is not connected to the proposed or any other transport protocol) would be a very valuable addition to Boost. I would certainly be interested in it.