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  1. Wicket
  2. WICKET-5588

Mixing Ajax and push (Atmosphere/native-websockets) updates does not respect order

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      Description

      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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            • Assignee:
              papegaaij Emond Papegaaij
              Reporter:
              interface Daniel Stoch
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              • Created:
                Updated: