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From Daniel Mikusa <dmik...@gopivotal.com>
Subject Re: Tomcat 8.0.0-RC5: asynchron IO and back pressure with ReadListener
Date Wed, 08 Jan 2014 18:55:19 GMT
On Jan 8, 2014, at 12:04 PM, Yann Simon <yann.simon.fr@gmail.com> wrote:

> Hi,
> 
> I am trying to write a servlet that asynchronously read data from the
> servlet request input stream.
> I tested my servlet with tomcat 8.0.0-RC5.

If possible, you might want to try 8.0.0-RC10 or trunk and see if you're getting the same
behavior.

> 
> the symptoms:
> - I must synchronously read the input stream in onDataAvailable() so
> that the upload works
> 
> what I expected:
> I want to be more "reactive" (buzzword of the moment) and not read the
> input stream until I am ready (=until the previous chunk is processed)
> I though I could return from onDataAvailable() before having read all
> the data, read the data in another thread.

Do you have a code sample?  It would help to see what you're doing.

> I expected onDataAvailable() to be called again when I consumed all the data
> (servletInputStream.isReady becomes false)

Generally this sounds OK.  When you call ServletInputStream.isReady() and it returns false,
that should trigger the container to call onDataAvailable() when more data is available to
be read.  If you return from onDataAvailable() and ServletInputStream.isReady() is still true
the container won't call onDataAvailable() again.  You'll be responsible for calling it when
you're ready to read more.

> That way, I could implement back pressure on the browser as long as my
> servlet has not finished its work with the actual chunk
> 
> But if I do that, neither onDataAvailable() nor onAllDataRead() is called again.

Again, a code sample would be helpful.  Debugging non-blocking IO is tricky.  If you can include
a sample Servlet or test case, it would greatly increase your chance of getting feedback.

Dan

> 
> When I consume the input stream synchronously in onDataAvailable(), it
> works as expected.
> 
> Am I misunderstanding the asynchron IO in Tomcat 8?
> 
> Thanks in advance for any ideas!
> Yann
> 
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