On Dec 19, 2013, at 8:08 PM, David Bullock <david.bull...@machaira.com.au>
wrote:
> On 20 December 2013 04:10, Daniel Mikusa <dmik...@gopivotal.com> wrote:
>> When run, you'll see that it processes some of the requests but fails due to
>> a timeout. I've not been able to replicate the other exceptions with the
>> unit test though, so those may be unrelated.
>
>> @WebServlet(asyncSupported = true)
>> public class DataStreamingServlet extends HttpServlet {
>
>> @Override
>> protected void service(HttpServletRequest request,
>> HttpServletResponse response) throws ServletException, IOException
>> {
> ...
>> DataStreamWriteListener dswl = new
>> DataStreamWriteListener(asyncContext, blocks);
>> response.getOutputStream().setWriteListener(dswl);
>> }
>
>> private class DataStreamWriteListener implements WriteListener {
>>
>> @Override
>> public void onWritePossible() throws IOException {
>> ServletOutputStream output =
>> context.getResponse().getOutputStream();
>
>> Any thoughts on what's happening here?
>
> This is a total guess ... getOutputStream() is waiting on a lock it
> will never acquire?
No, it's non-blocking IO so it wouldn't (definitely shouldn't) wait here.
Instead it writes until it's told that it cannot write (output.isReady() ==
false) without blocking. At that point, the container is supposed to call my
code (onWritePossible) once it can write again. Unfortunately, once this
problem starts to occur onWritePossible doesn't get called back.
I did a little more testing and for requests that timeout, it does not appear
that onWritePossible ever gets called. I added some logging to the code to
indicate when it first calls onWritePossible, when it must wait to write more
data and when it's done writing data. While the test is warming up and the
requests are being processed OK, I see all three log statements. Once the
problem manifests, new requests do not trigger any logging. They just timeout
and continue to timeout until I restart the JVM.
> (Increase the timeout, do a thread-dump).
When I take a thread dump of the code, it just shows all of the threads doing
nothing. Increasing timeout doesn't seem to help. Failures still occur within
the same timeframe (i.e. same number requests to the server). The only affect
is to create a delay between when requests stop being processed and the stack
trace shows up.
> What happens if you instead pass the ServletOutputStream to the
> DataStreamWriteListener's constructor?
Unfortunately nothing. I still see the issue.
Thanks
Dan
>
> cheers,
> David.
>
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