[undertow-dev] HTTP Upgrade in Servlet 3.1 - how to use non-blocking input & output at the same time

[Stuart Douglas]

Przemyslaw Bielicki wrote:
> Hi,
>
> I posted my question on wildfly-dev
> (http://lists.jboss.org/pipermail/wildfly-dev/2014-March/001986.html)
> but I think this one is better, as the implementation is in
> undertow-servlet, not in wildfly itself.
>
> I would like to use non-blocking input and output at the same time. For
> the simplicity let's implement EchoProtocol - check the attachments.
>
> As you see, the writer is in a separate thread created by manually
> (which is a bit smelly IMHO).

This is not guaranteed to work, as the underlying request objects are 
not thread safe.

Another point is that I do the write
> directly without checking whether I can write without blocking. In fact,
> when I call ServletOutputStream.isReady() I get the Undertow error:
> "UT010034: Stream not in async mode"
>
> Checking the source code you are not really sure if it's a correct
> behaviour:
>
> io.undertow.servlet.spec.UpgradeServletOutputStream
> io.undertow.servlet.spec.ServletOutputStreamImpl
> @Override
> public boolean isReady() {
> if (listener == null) {
> *//TODO: is this the correct behaviour?*
> throw UndertowServletMessages.MESSAGES.streamNotInAsyncMode();
> }

That is just a question about what happens if you call isReady() when 
the stream is not in async mode. Basically the spec does not say what to 
do, so we just throw an exception. If you are getting this exception you 
are using the stream wrong.

If you want to use async IO you need to register a write listener.


>
> Another point - more to non-blocking itself. How can
> ServletOutputStream.write(byte b[]) be non-blocking at all? Let's
> imagine that the socket is ready to write and I call write with a buffer
> of 1000 bytes but the receiver is ready only to receive 500 bytes at
> this point. My call will be blocked, right?

We just buffer the input, and then write it out in the background, then 
call the write listener again when we are done.

Stuart


>
> Cheers,
> Przemyslaw
>
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