Details
Major Description
In MessageListenerServlet.java
if (message == null && client.getListener().getUndeliveredMessages().size() == 0) {
Continuation continuation = ContinuationSupport.getContinuation(request);
if (continuation.isExpired())
{ response.setStatus(HttpServletResponse.SC_OK); StringWriter swriter = new StringWriter(); PrintWriter writer = new PrintWriter(swriter); writer.println("<ajax-response>"); writer.print("</ajax-response>"); writer.flush(); String m = swriter.toString(); response.getWriter().println(m); return; } continuation.setTimeout(timeout);
continuation.suspend();
LOG.debug( "Suspending continuation " + continuation );
// Fetch the listeners
AjaxListener listener = client.getListener();
listener.access();
// register this continuation with our listener.
listener.setContinuation(continuation);
return;
}
Based on above code, the continuation is expected to be expired after given timeout when there is no message available for the ajax client and the ajax client will then receive an "empty" message. However based on the servlet 3 Continuation implementation in jetty (Servlet3Continuation.java) the only place where the continuation is set to expire is within the below method (there is a bug in this method as well).
public void addContinuationListener(final ContinuationListener listener)
{
AsyncListener wrapped = new AsyncListener()
{
public void onComplete(final AsyncEvent event) throws IOException
public void onError(AsyncEvent event) throws IOException
{ listener.onComplete(Servlet3Continuation.this); }
public void onStartAsync(AsyncEvent event) throws IOException
{ event.getAsyncContext().addListener(this); }public void onTimeout(AsyncEvent event) throws IOException
{ _expired=true; listener.onTimeout(Servlet3Continuation.this); }};
if (_context==null)
_context.addListener(wrapped);
else
_listeners.add(wrapped);
}
Without adding a listener the continuation will never be set to expire, therefore the "empty" response is never sent back to the client, the connection from the client is resumed and suspended over and over again until the connection is aborted by client or there is a message available.