[undertow-dev] Async sending of NIO objects thru a ServletOutputStream?

[Stuart Douglas]

Generally we use org.xnio.ChannelListeners#initiateTransfer, however 
that is when we are just transfering between two channels, without any 
ServletOutputStream in use.

Basically you just read from the channel, if read returns >0 then call 
buffer.flip() and write it to the channel. When the callback is invoked 
clear the buffer, and repeat until read returns -1.

I don't know what you do if read returns 0, generally you will just use 
whatever async capability the channel has to register some kind of 
listener, but that is not provided by the ReadableByteChannel contract.

You do have to make sure that that buffer is freed when you are done 
with it though, as buffer leaks are bad news.

Stuart

Jim Crossley wrote:
> Stuart Douglas <sdouglas at redhat.com <mailto:sdouglas at redhat.com>> writes:
>
> [...]
>
>  > Yea, we don't have an easy way to just do that transfer at this stage,
>  > you will need to read into the pooled buffer then write it out.
>  >
>  > Is this an async or a blocking transfer? The problem with
>  > ReadableByteChannel is that it can be a blocking channel, and as a
>  > result reading from it in the IO thread will result in crappy
>  > performance.
>
> Because of the way they're using it (with Clojure's core.async library)
> I expect the transfer to be async, but I'll verify that with them.
>
> You wouldn't happen to have an example of reading one into and out of a
> pooled buffer you could point me to, would you? :)
>
> Jim
>
>
> On Tue, Sep 16, 2014 at 8:37 PM, Stuart Douglas <sdouglas at redhat.com
> <mailto:sdouglas at redhat.com>> wrote:
>
>
>
>     Jim Crossley wrote:
>
>         I actually figured that out, Stuart, thanks. So I have writing a
>         ByteBuffer covered. Any thoughts on handling the
>         ReadableByteChannel?
>         Looking at the Jetty impl, it appears I need to read it into one
>         or more
>         ByteBuffers and then write them out. Should I use the
>         Pooled<ByteBuffer>
>         from the exhange's connection?
>
>
>     Yea, we don't have an easy way to just do that transfer at this
>     stage, you will need to read into the pooled buffer then write it out.
>
>     Is this an async or a blocking transfer? The problem with
>     ReadableByteChannel is that it can be a blocking channel, and as a
>     result reading from it in the IO thread will result in crappy
>     performance.
>
>     Stuart
>
>
>         Jim
>
>         On Tue, Sep 16, 2014 at 6:00 PM, Stuart Douglas
>         <sdouglas at redhat.com <mailto:sdouglas at redhat.com>
>         <mailto:sdouglas at redhat.com <mailto:sdouglas at redhat.com>>> wrote:
>
>
>
>              Jim Crossley wrote:
>
>                  Hi guys,
>
>                  I'm looking to promote Undertow as a preferred
>         alternative to
>                  Jetty for
>                  the Pedestal [1] framework.
>
>                  One Jetty feature it relies on is the async sending of
>                  ByteBuffers and
>                  ReadableByteChannels in Jetty's impl of
>         ServletOutputStream [2]. Two
>                  methods, in particular: sendContent(ByteBuffer,
>         Callback) and
>                  sendContent(____ReadableByteChannel, Callback).
>
>
>              If you have enabled async mode on the ServletOutputStream then
>              write(ByteBuffer) will write using async IO, and invoke the
>         write
>              listener when done. Basically it will work the same as standard
>              servlet async IO, but with byte buffers.
>
>              Stuart
>
>
>                  I was hoping someone might point me in the right
>         direction of
>                  replicating this behavior with Undertow's
>                  ServletOutputStreamImpl. It
>                  does have a write(ByteBuffer) method, but it appears to be
>                  blocking. And
>                  I was hoping there might be some XNIO abstraction for
>         dealing
>                  with the
>                  ReadableByteChannel, perhaps some example code somewhere?
>
>                  Any and all help/advice is appreciated!
>                  Jim
>
>                  [1]: https://github.com/pedestal/____pedestal
>         <https://github.com/pedestal/__pedestal>
>         <https://github.com/pedestal/__pedestal
>         <https://github.com/pedestal/pedestal>>
>                  [2]:
>         http://grepcode.com/file/____repo1.maven.org/maven2/org.____eclipse.jetty/jetty-server/9.____2.0.v20140526/org/eclipse/____jetty/server/HttpOutput.java
>         <http://grepcode.com/file/__repo1.maven.org/maven2/org.__eclipse.jetty/jetty-server/9.__2.0.v20140526/org/eclipse/__jetty/server/HttpOutput.java>
>         <http://grepcode.com/file/__repo1.maven.org/maven2/org.__eclipse.jetty/jetty-server/9.__2.0.v20140526/org/eclipse/__jetty/server/HttpOutput.java
>         <http://grepcode.com/file/repo1.maven.org/maven2/org.eclipse.jetty/jetty-server/9.2.0.v20140526/org/eclipse/jetty/server/HttpOutput.java>>
>
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