[jira] [Commented] (WICKET-5588) Mixing Ajax and push (Atmosphere/native-websockets) updates does not respect order

["Daniel Stoch (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/WICKET-5588?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17265150#comment-17265150 ] 

Daniel Stoch commented on WICKET-5588:
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We are using our custom solution for this problem from over 2-3 years and it works ok (we have many automated tests which also prove this ;)).

It is not a very elegant code, because I had to hack Wicket here and there. And also I am not an expert in JS and Wicket JS code ;).
- To add ordering information (internal refresh page version) to responses for both ajax and websocket I am using a Label with this refresh version incremented on each ajax or websocket request. This label is always added to AjaxRequestTarget so I can read this refresh version for each call on JS side. I cannot find any other, better way to do this.
- I changed wicket-ajax-jquery.js to use refresh calls list. These refresh calls are processed in the same order as a responses generated on the server side. To do this I am using $.Deferred() object and some timeout handling (default=5sec) for waiting on another response. I have added this patched version of this file (wicket-ajax-jquery-ext.js).

> Mixing Ajax and push (Atmosphere/native-websockets) updates does not respect order
> ----------------------------------------------------------------------------------
>
>                 Key: WICKET-5588
>                 URL: https://issues.apache.org/jira/browse/WICKET-5588
>             Project: Wicket
>          Issue Type: Improvement
>          Components: wicket, wicket-atmosphere, wicket-native-websocket
>    Affects Versions: 6.15.0, 6.21.0
>            Reporter: Daniel Stoch
>            Assignee: Emond Papegaaij
>            Priority: Major
>         Attachments: 5588-ajax-thru-websocket.tgz
>
>
> As far as I know in Wicket ajax calls by default using the same channel and they are queued. But in wicket-atmosphere integration on the client side the refreshing is done by calling (inside wicket-atomosphere.js):
>   Wicket.Ajax.process(response.responseBody);
> It looks like Wicket.Ajax.process() function does not use channels management, so it can result in out-of-order response processing. This method was added to support Atmosphere push calls in Wicket. See the commit (for issue: WICKET-4668):
> https://github.com/apache/wicket/commit/130b063722e55510f2b2a3b47889e14210a5a32f
> *Example scenario to reproduce this problem:*
> When we try to refresh a component (panelA) via ajax when two different threads in the "same" time perform such refresh.
> 1. The first thread (thread1) is a standard servlet container thread to handle user request from a browser:
> - user clicks AjaxLink and on onClick method panelA is refreshed by target.add(panelA).
> 2. The second thread (thread2) is a notification from a backend system which causes a panelA refreshing too:
> - it can be done for eg. using Atmosphere integration by EventBus.post() - panelA is refreshed by target.add(panelA) too.
> On the server side only one thread can access a page at a time so everything is "queued" properly: the thread1 panelA refresh is executed, then the thread2 refresh code is fired.
> But it looks like on the client side the order of ajax calls is undefined: sometimes JS code added from the thread1 is executed as first, sometimes as a second one. On my computer this order almost always is wrong. It leads to an incorrect situation when the component state on a server is different than the DOM tree on the client browser (so for example user can clicks not existing link).



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