[richfaces-issues] [JBoss JIRA] (RF-12072) Lost event in push

Fri Mar 23 07:49:47 EDT 2012

    [ https://issues.jboss.org/browse/RF-12072?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12678923#comment-12678923 ] 

Stian Thorgersen commented on RF-12072:
---------------------------------------

By wrapping "Thread.sleep(10000);" with "if (c > 0)" the example doesn't work, as you allow the page to be rendered fully before the first event is sent, hence bypassing the problem.

In my application I use the push component to refresh the views when new data is available. The application allows users to "add/change" data asynchronously, so the data may be already changed when the model values are updated, or it may be changed later. In certain situations, especially when the server is running on a slow machine, the client can miss the update events altogether:

* Client presses commandButton
* Asynchronous change to data started
* JSF model values updated
* Data updated + update event is fired
* Page is viewed in browser, but update event is lost

It works fine in either of the following scenarios:

* Client presses commandButton
* Asynchronous change to data started
* Data updated + update event is fired
* JSF model values updated (missed event isn't a problem as data is changed before model values are updated)
* Page is viewed in browser

and:

* Client presses commandButton
* Asynchronous change to data started
* JSF model values updated
* Page is viewed in browser
* Data updated + update event is fired (page is refreshed by push component and new values are retrieved from server)

The example tries to force the first scenario where the data is lost by making sure the page is viewed after the event is fired.

> Lost event in push
> ------------------
>
>                 Key: RF-12072
>                 URL: https://issues.jboss.org/browse/RF-12072
>             Project: RichFaces
>          Issue Type: Bug
>      Security Level: Public(Everyone can see) 
>          Components: component-push/poll
>            Reporter: Stian Thorgersen
>            Assignee: Lukáš Fryč
>
> Event can be lost if produced while a response is being prepared. I've attached an example where a push event is used to refresh a count whenever an event is fired. It's using Thread.sleep to simulate an event being produced while the response is being prepared. Note, if the sleep just before returning the count is removed it all works fine, and the page is refreshed every 5 seconds, but with the sleep in place the event is lost.
> View:
> {code}
> <?xml version="1.0" encoding="utf-8"?>
> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en-GB" lang="en-GB"
> 	xmlns:f="http://java.sun.com/jsf/core"
> 	xmlns:h="http://java.sun.com/jsf/html"
> 	xmlns:a4j="http://richfaces.org/a4j"
> 	xmlns:rich="http://richfaces.org/rich">
> <h:head>
> 	<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
> </h:head>
> <h:body>
> 	<h:form id="myForm">
> 		<a4j:push address="chat">
> 			<a4j:ajax event="dataavailable" render="count" />
> 		</a4j:push>
> 		<h:outputText value="#{myBean.count}" id="count" />
> 	</h:form>
> </h:body>
> </html>
> {code}
> Bean:
> {code}
> package com.example;
> import java.io.Serializable;
> import java.util.concurrent.atomic.AtomicInteger;
> import javax.enterprise.context.SessionScoped;
> import javax.inject.Named;
> import org.richfaces.application.push.TopicKey;
> import org.richfaces.application.push.TopicsContext;
> @Named
> @SessionScoped
> public class MyBean implements Serializable
> {
>     private AtomicInteger count = new AtomicInteger();
>     public int getCount()
>     {
>         int c = count.get();
>         new Thread()
>         {
>             public void run()
>             {
>                 try
>                 {
>                     Thread.sleep(5000);
>                     count.incrementAndGet();
>                     TopicKey topicKey = new TopicKey("chat");
>                     TopicsContext topicsContext = TopicsContext.lookup();
>                     topicsContext.publish(topicKey, "");
>                 }
>                 catch (Exception e)
>                 {
>                     e.printStackTrace();
>                 }
>             };
>         }.start();
>         
>         try
>         {
>             Thread.sleep(10000);
>         }
>         catch (InterruptedException e)
>         {
>         }
>         return c;
>     }
> }
> {code}

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