NIO2 async threading

[Alan Bateman]

Rob Butler wrote:
> :
> Thanks, that really cleared things up.
>
> Jean-Francois has done lots of R&D with NIO.  He's found that using temporary selectors and doing IO operations on the same thread (only when waiting briefly for more data to complete a request) leads to higher throughput (and I would suspect lower latency) than using separate 'worker' and 'IO' threads.  (http://weblogs.java.net/blog/jfarcand/archive/2006/07/tricks_and_tips_4.html) Such an approach wouldn't be possible with Async NIO, would it?  I.E. you get a callback to tell you about new data arrival, but there is no way to hang out (and momentarily block in the callback thread) waiting for more data, is there?
>
> If that's the case, while dealing with selectors is a pain, the existing NIO API may ultimately be faster and have lower latency than the NIO2 async API's.  Please point out anything I may have missed that would make this not the case.
>   
It's probably best not to jump to any conclusions here. The underlying 
implementations are very different. For the scenario you describe, if a 
completion handler is consuming the result of a read operation and it 
initiates another read operation (because its buffer has sufficient 
remaining space, or due to a short-read) then its handler will execute 
immediately on the current thread if there is data available (no context 
switch, no additional latency). There isn't direct support to "bet" on 
data arriving in a few seconds but as there may be several threads 
polling events from the kernel then there shouldn't be any delay when 
the data arrives (note that this is very different to the existing API 
where a single thread polls with the Selector). Jean-Francois and I talk 
very regularly. He's on this mailing list and may wish to say something 
about the work he has done so far to port Grizzly to the new API. I 
believe there is still work to do so I don't think there is performance 
numbers to share yet. When he is done perhaps we can get him to write up 
an equivalent tricks 'n tips for the new API :-)

-Alan.