Question

I am trying to implement long polling in my Spring-MVC Web App but it freezes my browser and other request after 4-5 continues AJAX requests.I have no clue whats goin on here is my relevant code.

The controller method:(Server Side):-

@Asynchronous
    @RequestMapping("/notify")
    public @ResponseBody
    Events notifyEvent(HttpServletRequest request) {
        Events events = null;
        try {
            events = (Events) request.getSession(false).getServletContext().getAttribute("events");
            System.out.println("Request Came from" + ((com.hcdc.coedp.safe.domain.User) request.getSession(false).getAttribute(Constants.KEY_LOGGED_IN_USER)).getLoginId());
            if (!events.getTypeOfEvents().isEmpty()) {
                System.out.println("Removing older entries");
                events.getTypeOfEvents().clear();
            }
            while (!events.isHappend()) {
                //Waiting for event to happen.
            }
            events = Events.getInstance();
            events.setHappend(false);
            request.getSession(false).getServletContext().setAttribute("events", events);

        }catch (Exception e) {
            e.printStackTrace();
        }
        return events;
    }

The long-polling script(Client Side):-

$(document).ready(function() {
                    $.ajaxSetup({
                        async:true//set a global ajax requests as asynchronus
                    });
                     alert('Handler for .onload() called.');
                    waitForMsg();

                });
                function waitForMsg(){

                    xhr=  $.ajax({
                        type: "POST",
                        url: '<%=request.getContextPath()%>/notification/notify',

                        async: true, /* If set to non-async, browser shows page as "Loading.."*/
                        cache: false,
                        timeout:50000, /* Timeout in ms */
                        global:false,
                        success: function(data){ /* called when request to notifier completes */
                          /* Doing smthing with response **/
                            setTimeout(
                            waitForMsg, /* Request next message */
                            1000 /* ..after 1 seconds */
                        );
                        },
                        error: function(XMLHttpRequest, textStatus, errorThrown){
                            addmsg("error", textStatus + " (" + errorThrown + ")");
                            setTimeout(
                            waitForMsg, /* Try again after.. */
                            15000); /* milliseconds (15seconds) */
                        }
                    });
                };

UPDATE:

function updateFeed(event, data) {
                var f=eval(data);
                alert(f.typeOfEvents.length);
            }

            function catchAll(event, data, type) {
                console.log(data);
                alert("error");
                console.log(type);
            }

            $.comet.connect('<%=request.getContextPath()%>/notification/notify');
            $(document).bind('feed.comet', updateFeed);
            $(document).bind('.comet', catchAll);

Neither alert box pops up..:(

Answer 1

It seems you have an empty while loop in your browser code.. this is a very CPU instensive way to wait for an event.

If no events happen the client will kill the request after your desired timeout of 50 seconds. But I’m not sure if the server thread is killed too, or if it “whiles” on forever (unless there is an event). The next request will start a second server thread that hangs in the while loop too then. Maybe the amount of empty while loops is an overkill for the server, so that it stops accepting any more requests. So after some requests (that each triggered an endless server thread) the client waits forever on a new request.. because it can’t be handled by the server.

ps: on success you commented to wait 1 second, but set the timeout to 10000 (10 seconds)