Re: [undertow-dev] Undertow and non-blocking File IO
On Nov 25, 2015, at 3:27 PM, Stuart Douglas
<sdouglas(a)redhat.com> wrote:
----- Original Message -----
> From: "Andrew Brampton" <me(a)bramp.net>
> To: undertow-dev(a)lists.jboss.org
> Sent: Wednesday, 25 November, 2015 4:13:03 PM
> Subject: [undertow-dev] Undertow and non-blocking File IO
>
> I just started playing with Undertow, but I had a couple of questions about
> the use of non-blocking operations vs using the worker thread pool.
>
> In the ResourceHandler.java it appears to dispatch itself onto a worker
> thread, and then uses blocking file IO to actually read the file. I'm
> curious why a AsynchronousFileChannel wasn't used to read from the file in a
> non-blocking way? This would be in keeping with the non-blocking IO threads.
This is something we should look at, however this only has an actual benefit on Windows
AFAIK. Other platforms use SimpleAsynchronousFileChannelImpl which simply delegates to a
thread pool.
The major issue that prevents this is that Linux filesystems (in combination with the
kernel) can sometimes block in io_submit (e.g. during certain metadata operations). You
also have to open a file aligned and in O_DIRECT which Java NIO does not support. If you
look at what the glibc impl does, it actually ends up creating a thread pool of its own.
>
> I wrote a quick HttpHandler that used the AsynchronousFileChannel and it
> worked really well. However, when creating AsynchronousFileChannel you have
> to specify the ExecutorService to be used to schedule the completion handler
> callback on. I was able to use exchange.getIoThread().getWorker(), but I'm
> curious if there is a way to schedule it back on the IO Threads? It just
> seems "purer" keeping everything on a single IO thread per core.
The IO threads implement Executor not ExecutorService, you could write a wrapper, but if
you used it on non Windows platforms you would block the IO thread.
Stuart
>
> thanks
> Andrew
>
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