> > > Sounds better - but as Remy explained you would first need to explain > why blocking is needed in this context and how to deal with the confusion > of mixing blocking and non-blocking for users, and the implementation > complexities it adds. trunk doesn't mix them. a comet connection is either blocking or non blocking, it doesn't shift between the two, and it allows developers to choose what they want. Just like a SocketChannel in java.nio. there is nothing confusing about that, unless java.nio is confusing :)
Well, nio is far from perfect - but that's not the point. Servlets have a very nice blocking mechanism already - it's the servlet API :-). The question is why would you need to have a Commet connection blocking. I think it's very reasonable to add a blocking waitForEvent() to allow servlets have a simpler ( but less efficient ) implementation. Think about utilities that take the event as param - would they need to check first if it's blocking or not ? And what would blocking give you in addition to waitForEvent() - which is actually better since it allows you to un-block on any event, not only a specific read/write.
> >> >> > - please don't call the method configure(), it's commonly used with a >> > different meaning ( i.e. setting the port or general configuration). >> > setConnectionMode, etc. And using the enum doesn't sound consistent >> with >> > other APIs either. >> we can call it whatever we want. But saying not using enum, its not >> consistent with other APIs in Tomcat, >> means would never take advantage of new language features ever, I think >> that would be a shame. > > > Same as above - the question is not about using new features, but if the > features > fit the use. I have no problem with using enums for the event types - > just > for > configure, in the context of configure(enum) versus setBlocking(), > setFoo(). this has been adjusted based on the feedback, the method is now configureBlocking(boolean) the state of it can be used by calling isBlocking() register is using enums, mainly cause Remy, while he was working with this API insisted on it. I had preferred using an int, just like the socket API, but since Remy had initially agreed to register, and proposed enum and unregister we went with that.
Ok.
> > > > >> > - see bellow - I don't think I understand the benefits of mixing >> blocking >> > and non-blocking in this interface, it is quite confusing. >> It would be mixing it, its a one time config, during the BEGIN event, >> you say >> configureBlocking(true) or configureBlocking(false). >> Comet is very much connection centric, so you can't mix it. >> >> In the trunk API, its clear to what you are using, blocking or non >> blocking, in the sandbox API, the swap >> of it happens when invoking isWriteable or isReadable, making the state >> of the comet connection confusing to the developer. > > > I'm not sure it's true - my understanding is that sandbox is all > non-blocking. > Invoking isWriteable is not blocking. > > I think it would be ok to add a blocking waitForEvent() - combined with > isReadable()/isWriteable() this would be a dead lock, as the Comet API must guarantee that a CometProcessor.event is only invoked by one worker thread at any time. The blocking you are talking about can be done using an async thread can be done by registering for the event you wish to be notified in and then maybe await a latch countdown, or doing a sync/wait() combo.
What would happen in the blocking case when a different event happens ? Isn't it the same, if you want to guarantee single-threaded behaviour ? Well - is there any docs on what is the intended thread model of comet servlets, i.e. SingelThreaded or reentrant ? Multiple events can happen at same time ( or very close - one event soon after a Comet servlet is called, before it returns), so this is a general problem.
it will allow a sort-of blocking model. But having methods that are > blocking > sometimes > and sometimes not - based on some config - is dangerous and confusing. As I mentioned, the trunk Comet API is actually very similar to java.nio API, hence developers familiar with that will instantly recognize themselves and should get comfortable with the API.
I still don't recognize it as NIO :-), and I am not very comfortable with the changes between blocking and non-blocking in NIO ( including all the crazy things that can happen only in the IO thread ). Here are some of the things that might need to be clarified about the
trunk API: 1. It is possible to not be registered for any events, and even do polling for data asynchronously
You would still get the BEGIN event I assume. All you need to poll data async is waitForEvent(), or select() if you like to emulate nio. 2. ERROR and END events, are an exception, you cant unregister for
those, as those might require the underlying socket to be closed, or has already been closed
In what thread would you get those ( in blocking mode ?) 5. The current READ event in CoyoteAdapter ends up performing a blocking
read if data has been received but its not enough for ServletInputStream.read() to actually generate data, just so that it can produce a real READ event, there is no real way to get around this without a major effort described in 4)
6. sleep() and callback() are names that already have confused folks in this thread, they just don't make sense.
I agree, but easy to change :-) But its not the names alone, people think of Comet as
request/response stuff, when it isn't. Comet is centered around a socket connection, and the events generated are a direct derivative of that. That is why I have chosen to make the API similar to what's been in Java since 1.4
As long as it doesn't require you to do special things in the select() thread, I'm happy :-) Comet is definitely more advanced than a servlet, and the complexity
of it is higher, having less methods on an API wont make it less complex, since the complexity sits in understanding the concept. I'm gonna work up some examples so that we can take a look at different scenarios and how the APIs would differ Filip > > Costin > > Filip >> > >> > In the sandbox version: >> > - sleep() and setTimeout(int) -> why not sleep(int millis) ? I think >> it's >> > confusing to have both and the interactions between them, in >> > particular setTimeout is marked optional ? It makes sense to have >> > setTimeout() as a general timeout. >> > >> > - not sure I understand the use case for isReadable()/isWriteable() - >> > when >> > will this be called ? My understanding was that when >> > the connection is readable, a callback will be generated with >> > EventType == >> > READ. Also it's very confusing to mix the 'blocking' in the >> > isReadable()/isWriteable() - it would be much cleaner to say that the >> > connection is always non-blocking, and add a method to switch to >> blocking >> > mode ( then use the regular servlet methods maybe ). Using the >> > ComentEvent >> > for both is IMHO dangerous. >> > >> > - will sleep() still allow callbacks ( and if not - what will happen >> with >> > them )? What's going to happen with callbacks if callback() is not >> > called ? >> > >> > >> > In general ( both versions): >> > - it would be great to move it from o.a.catalina to org.apache.comet >> > >> > Costin >> > >> > On 6/11/07, Remy Maucherat <[EMAIL PROTECTED]> wrote: >> >> >> >> Filip Hanik - Dev Lists wrote: >> >> > Ok, let me see if I can summarize. >> >> > >> >> > 1. Whether you write out the stored buffer using the Poller thread, >> >> or a >> >> > Tomcat worker thread (flushed in Http11xxxProcessor) as described >> >> below >> >> > I originally thought of this as async write, as we are simply >> doing a >> >> > write with another one of our threads. Originally when we were >> talking >> >> > non blocking writes, I was thinking along the lines of non blocking >> to >> >> > where the Comet developer had to do that logic, just as he was >> >> writing a >> >> > socket, possibly like (but not suggested) a >> >> > CometEvent.nonBlockWrite(ByteBuffer). >> >> > >> >> > 2. Do we need non blocking? with the methods of isWriteable and the >> >> > ability to register(OP_WRITE)->event(WRITE), if the number of bytes >> >> you >> >> > write is usually smaller than the socket buffer, chances are that >> most >> >> > writes will be non blocking. I would even argue a large majority >> would >> >> > be non blocking, and thus the implementation or the complexity >> thereof >> >> > would not be needed. And with the ability to do async writes, >> means I >> >> > can create my own thread pool/write queue to perform these writes. >> >> >> >> You are writing the opposite thing to the previous email, and we are >> >> back to "non blocking is useless". The problem is that I understand >> >> blocking IO as "write this data, and return when it's done". If the >> >> socket is in blocking mode, any write done by the servlet may block, >> >> regardless of what isWriteable says. Of course, it's very unlikely, >> >> which is why Comet in 6.0.x works. >> >> >> >> > 3. isWriteable - simple method, but I don't like that the method in >> >> > itself performs actions like adding the socket to a poller etc. >> >> > Instead isWriteable==true means that you can write on the socket, >> >> > isWriteable==false you cannot. This method should be able to be >> >> invoked >> >> > as many times as its wanted, and is thread safe and doesn't do >> >> anything >> >> > funky underneath. >> >> >> >> Ok, so you prefer a more complex API (if I follow "just in case it >> was >> >> useful"). I started with an API which would expose all operations, >> and >> >> looked into removing what was not explicitly useful. >> >> >> >> > 4. isWriteable - I'm also reading in that you are also suggesting >> that >> >> > we use this method to declare if we want blocking or non blocking >> >> writes. >> >> >> >> No. The situation where write could (maybe) block is if the servlet >> >> writes in a Tomcat thread. Typically, this is the reply-later design, >> >> using the sleep/callback methods. The isWriteable method is not used, >> >> since the servlet merely wants (in that common design) to send a >> >> response as fast as possible, and typically this sort of response is >> not >> >> too large and unlikely to cause IO problems. This blocking >> behavior is >> >> allowed in that case to avoid forcing the user to put in more complex >> >> logic to deal with the partial write + event, and is set just for the >> >> amount of time it takes to perform the write (note that this ). >> >> >> >> > At this point this method is doing three things: >> >> > a) returns true/false if we can write data >> >> > b) delegates a socket to the poller to write data and generate a >> >> > event(WRITE) to the comet processor >> >> > c) configures a write to be blocking or non blocking >> >> > This is for sure not what I would expect of a "simple API", if >> >> simple >> >> > means less keystrokes than yes, but simple to me also means >> intuitive >> >> > and easily understood. >> >> >> >> So you have plenty of methods to do the same thing. >> >> >> >> > Given points 1-4, this is what is going to happen to every single >> >> developer >> >> > I) They are going to use stream.write and event.isWriteable all >> the >> >> > time, not realizing what it actually does >> >> > II) They are going to get confused when they receive an IOException >> >> for >> >> > trying to perform a write, cause they used isWriteable and the >> socket >> >> > went into non blocking mode >> >> >> >> If that's what you want to believe ... >> >> >> >> > At this point, this 'simple' API, obviously not so simple, >> instead it >> >> > becomes very complicated, as I would almost have to reverse >> >> engineer the >> >> > code to truly understand what it does. >> >> > It may be simple to you and me, but that is because we are >> >> implementing >> >> it. >> >> >> >> I really don't see what is complex, especially when you look at the >> code >> >> the user would write for the simple cases, where you don't even >> have to >> >> use any API besides stream.write: >> >> - reply later >> >> - wait for read events, and write data in response to it >> >> >> >> The complex case deals with handling incomplete async writes if you >> >> don't simply drop connection. >> >> >> >> > so what does this mean to 'isReadable'? That I'm automatically >> >> > registering for a READ event if it returns false? Maybe I don't >> want >> a >> >> > READ event, I just want to see if any data has trickled in. so if I >> >> call >> >> >> >> > sleep(), should I then call isReadable() to reregister for the >> >> read. how >> >> > is this simpler than that register/unregister. >> >> >> >> Read events always occur, unless you use sleep/callback. If this >> is not >> >> written clearly in the javadocs already, I need to change them. >> >> >> >> > Where does that leave us, well: >> >> > a) We are almost in sync on the implementation side of it >> >> >> >> Not really, there's a big disconnect in the understanding of non >> >> blocking vs blocking, and according to you, non blocking is not >> useful >> >> (again). >> >> >> >> > b) I believe your API is not intuitive, nor usable, as it simply >> >> doesn't >> >> > reflect what is going on and/or what a programmer wants done >> >> > c) Your API doesn't become simpler just cause we merge three >> methods >> >> > into one -> configure(NON_BLOCK), write(byte[]), register(OP_WRITE) >> >> > c) The API I propose, you think is overengineered, I think it just >> >> makes >> >> > things much clearer, the fact that it automatically allows for >> future >> >> > extension is a side effect rather than design decision >> >> >> >> My API is simpler because the code the user has to write is more >> >> straightforward and easier to understand. Feel free to write small >> >> examples to see for yourself. >> >> >> >> > So bottom line is, user will get the same implementation (or very >> >> close >> >> > to what we've talked about), question is what API are they going to >> >> get? >> >> >> >> RÃ(c)my >> >> >> >> --------------------------------------------------------------------- >> >> To unsubscribe, e-mail: [EMAIL PROTECTED] >> >> For additional commands, e-mail: [EMAIL PROTECTED] >> >> >> >> >> > >> ------------------------------------------------------------------------ >> > >> > Internal Virus Database is out-of-date. >> > Checked by AVG Free Edition. >> > Version: 7.5.472 / Virus Database: 269.8.11/837 - Release Date: >> 6/6/2007 >> 2:03 PM >> > >> >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: [EMAIL PROTECTED] >> For additional commands, e-mail: [EMAIL PROTECTED] >> >> > ------------------------------------------------------------------------ > > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.5.472 / Virus Database: 269.8.15/848 - Release Date: 6/13/2007 12:50 PM > --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]