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?
Rémy
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