I've enhanced SSHD to be able to provide fully non-blocking io on both client channels and server commands. A client side example is shown at
https://github.com/apache/mina-sshd/blob/master/sshd-core/src/test/java/org/apache/sshd/ClientTest.java#L171 A server side example: https://github.com/apache/mina-sshd/blob/master/sshd-core/src/test/java/org/apache/sshd/util/AsyncEchoShellFactory.java I would appreciate any input ... 2014-04-20 0:33 GMT+02:00 Alon Bar-Lev <[email protected]>: > On Sun, Apr 20, 2014 at 1:19 AM, Guillaume Nodet <[email protected]> > wrote: > > 2014-04-19 20:43 GMT+02:00 Alon Bar-Lev <[email protected]>: > > > >> On Sat, Apr 19, 2014 at 9:15 PM, Guillaume Nodet <[email protected]> > >> wrote: > >> > Sshd internally uses nio2 by default, which is not based on selectors, > >> but > >> > non blocking operations. > >> > > >> > On the client part of SSHD, things are mostly asynchronous already: > >> > #1 SshClient#connect returns a future on which you can set a > callback > >> > and that you can use to retrieve the ClientSession asynchronously > >> > #2 You need to use ClientSession#addXxxIdentity and then > >> > ClientSession#auth which is also asynchronous > >> > #3 You then create a channel, and actually operning the channel is > >> also > >> > asynchronous > >> > #4 Closing channels is also asynchronous > >> > > >> > I think the only missing part is really the streams on the > ClientChannel > >> > which are using InputStream and OutputStream. > >> > If we replace them with an AsynchronousByteChannel, I think we would > be > >> > fully async. > >> > >> Thank you for your response, Our definition of async is very > different... > >> :) > >> > >> I do not think this module is sufficient to what I target. I see the > >> number of threads created within the library core and the logic that > >> is out of reach. > > > > > >> This ssh library is great, splitting it into two logic only and > >> communication layers will enable to go fully async. The logic layer > >> should not have any thread. A default implementation of communication > >> layer can be provided, but is optional. The difference from the world > >> I coming for is that Future handling is much more complex than having > >> control queue. > >> > > > > Not sure exactly what you're talking about here. > > > > Afaik, the only place where the ssh layer actually create a thread in > when > > creating > > a client ChannelSession giving an InputStream which has to be read. This > > thread creation can be easily avoided by using > ClientChannel#getInvertedIn() > > and writing to it. > > > > All other threads are communication threads only and are fully controlled > > by > > the IoService layer which is pluggable. Both mina and nio2 > implementations > > use a fixed number of threads. But you can rewrite it if you need. > > > > I'm all for improving sshd, but I fear i'm not really seeing your points > > clearly. > > Thank you for the discussion, I truly appreciate that. > > Having a method for async input/output of data stream will be a good > start within current implementation. > > Other than that it is a programming pattern discussion. I got the > information I needed, thank you! > > >> > >> Was just an idea, thank you for addressing. > >> > >> > > >> > 2014-04-19 15:57 GMT+02:00 Alon Bar-Lev <[email protected]>: > >> > > >> >> On Sat, Apr 19, 2014 at 3:52 PM, Jon V. <[email protected]> > wrote: > >> >> > > >> >> > NIO controls and deals with the selectors. Async IO is a part of > that > >> but > >> >> > is not the same thing. Async io means that if a write cannot be > fully > >> >> > flushed. It will not block until it can be. NIO provides us the > >> events to > >> >> > tell us that data is available in the socket. > >> >> > >> >> Async IO is the ability for a single thread to perform (multiplex) IO > >> >> (connect, read, write, close etc..) for multiple file descriptors. > >> >> > >> >> As far as I know, without NIO you cannot achieve that in Java. > >> >> > >> >> There is no sense in read or write without blocking if you cannot > wait > >> >> (vs actively poll) for an event. > >> >> > >> >> > On Apr 19, 2014 4:56 AM, "Alon Bar-Lev" <[email protected]> > >> wrote: > >> >> > > >> >> > > On Sat, Apr 19, 2014 at 10:58 AM, Emmanuel Lécharny < > >> >> [email protected]> > >> >> > > wrote: > >> >> > > > Le 4/19/14 9:45 AM, Alon Bar-Lev a écrit : > >> >> > > >> On Sat, Apr 19, 2014 at 10:38 AM, Emmanuel Lécharny < > >> >> > > [email protected]> wrote: > >> >> > > >>> Le 4/19/14 9:13 AM, Alon Bar-Lev a écrit : > >> >> > > >>>> Hi, > >> >> > > >>>> > >> >> > > >>>> The mission of async is to avoid having threads at all, or > at > >> >> least > >> >> > > O(1). > >> >> > > >>>> > >> >> > > >>>> As you have underline internal/private low level channels > for > >> >> socket > >> >> > > >>>> processing, and public high level channels to communicate > with > >> >> > > >>>> application, there should be a mechanism for library to > request > >> >> wake > >> >> > > >>>> up for these low level channels. > >> >> > > >>>> > >> >> > > >>>> Another option is to avoid using sockets at all within the > >> >> > > >>>> implementation and require application to manage the sockets > >> and > >> >> pipe > >> >> > > >>>> socket data into the library. > >> >> > > >>>> > >> >> > > >>>> I understand this is conceptional change than what we have > now, > >> >> but > >> >> > > >>>> this what will enable scale without abusing system threads > or > >> have > >> >> > > >>>> nondeterministic behaviour in high load. > >> >> > > >>> There are a few important things you have to know about async > >> and > >> >> > > threads : > >> >> > > >>> - the extra cost for dealing with async connection is around > >> 30%. > >> >> That > >> >> > > >>> all but free > >> >> > > >>> - a standard system can easily deal with a few thousands of > >> threads > >> >> > > >>> > >> >> > > >>> Now, unless you define what is "high load", I don't really > see > >> what > >> >> > > kind > >> >> > > >>> of advantage we can get with an async implementation. > >> >> > > >>> > >> >> > > >>> FTR, when MINA was initially created, it was because there > was a > >> >> need > >> >> > > >>> for a system supporting potentially ten of thousands of > >> >> connections. Is > >> >> > > >>> that what you are targetting ? > >> >> > > >> Yes, using work threads that are derived per # of CPUs, no > more. > >> >> > > >> I am far from the pure "Java" world... but if async IO is 30% > >> >> > > >> insufficient, maybe it worth to use libssh (C) and communicate > >> with > >> >> it > >> >> > > >> using single socket from java, delegating IO outside of java. > >> >> > > > IO are already delegated outside on Java. Eveything IO related > is > >> >> > > > written in C and wrapped into Java class. > >> >> > > > > >> >> > > > The extra cost when using NIO is due to the management of > >> SelectorKey > >> >> > > > lists (with the various steps involved when dealing with those > >> >> lists). > >> >> > > > > >> >> > > > All in all, when it comes to process IO, Java does not really > add > >> >> some > >> >> > > > extra cost over a plain C implementation. It's not the same > story > >> >> when > >> >> > > > using NIO, especially when dealing with many concurrent > >> connections. > >> >> > > > > >> >> > > > >> >> > > So I am confused... Java does not add cost to async IO, but NIO > >> does? > >> >> > > While NIO is the only interface to Java async IO? > >> >> > > > >> >> > >> >
