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From "Jesse MacFadyen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CB-4873) XHRHelper is failing with simultaneous asynchronous requests
Date Tue, 29 Jul 2014 19:18:39 GMT

    [ https://issues.apache.org/jira/browse/CB-4873?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14078201#comment-14078201
] 

Jesse MacFadyen commented on CB-4873:
-------------------------------------

what version of cordova [~joejoerubio]?

> XHRHelper is failing with simultaneous asynchronous requests
> ------------------------------------------------------------
>
>                 Key: CB-4873
>                 URL: https://issues.apache.org/jira/browse/CB-4873
>             Project: Apache Cordova
>          Issue Type: Bug
>          Components: WP8
>    Affects Versions: 3.0.0
>         Environment: Any
>            Reporter: Jonathan Naguin
>            Assignee: Jesse MacFadyen
>            Priority: Critical
>              Labels: WP8, WP8.1, ajax, asynchronous, multiple, xhrhelper
>         Attachments: CordovaWP8_3.6.0-dev1.zip, CordovaWP8_WP8.1_3.4.1.zip
>
>
> XHRHelper is failing in processing mutiple simultaneous asynchronous AJAX requests. I
am using the latest code from https://github.com/apache/cordova-wp8/blob/master/wp8/template/cordovalib/XHRHelper.cs
> The problem is related with {{_onXHRLocalCallback}} which is save into the {{window}}
object as a unique function. When, for example, two Ajax requests are evaluated at same time,
the last {{funk}} function overrides the first {{_onXHRLocalCallback}} without receive the
data from the C# code to that particular request.
> To demostrate this I put {{console.log("XHR: " + resolvedUrl);}} inside {{__onXHRLocalCallback}}
and {{System.Diagnostics.Debug.WriteLine("HandleCommand: " + url);}} in {{HandleCommand}}
method (my code uses *Require JS* to load this resources). The output is this:
> {code}
> HandleCommand: x-wmapp0:www/src/modules/home/HomeView.html
> HandleCommand: x-wmapp0:www/src/modules/orders/OrdersView.html
> XHR: x-wmapp0:www/src/modules/orders/OrdersView.html
> XHR: x-wmapp0:www/src/modules/orders/OrdersView.html
> XHR: HandleCommand: x-wmapp0:www/src/modules/order/OrderDetailView.html
> XHR: x-wmapp0:www/src/modules/order/OrderDetailView.html
> {code}
> As you can see, one request is missing: "HomeView.html".
> h6. NOTES
> - If I set {{false}} the {{this.isAsync}} variable it works (this way it is executed
without using setTimeout).
> - If I put a console.log before launch {{funk}} it works.
> - It works on the simulator, but it fails on a real device.
> h6. Possible solution
> In conclusion, I assumed that it's a timing problem. To resolve it I decided to save
a onXHRLocalCallback function per each request:
> {code}
> var funk = function () {
>     if (! window.__onXHRLocalCallback){
>         window.__onXHRLocalCallback = {}; //Object to store the functions
>     }
>     
>     window.__onXHRLocalCallback[resolvedUrl] = function (responseCode, responseText)
{
>         alias.status = responseCode;
>         if (responseCode == '200') {
>             alias.responseText = responseText;
>         }
>         else {
>             alias.onerror && alias.onerror(responseCode);
>         }
>         alias.changeReadyState(XHRShim.DONE);
>         delete window.__onXHRLocalCallback[resolvedUrl]; //Delete the function
>     }
>     alias.changeReadyState(XHRShim.LOADING);
>     window.external.Notify('XHRLOCAL/' + resolvedUrl);
> }
> {code}
> So I had to change in {{HandleCommand}} method the way of invoking this callback. I decided
to create a helper function to be called in each case:
> {code}
> /// <summary>
> /// Invoke a XHR callback
> /// </summary>
> /// <param name="url">The URL of the request</param>
> /// <param name="code">The response code</param>
> /// <param name="text">The response text</param>
> private void InvokeCallback(string url, int code, string text)
> {
>     string args = string.Format("('{0}', {1}, {2});", code, WPCordovaClassLib.Cordova.JSON.JsonHelper.Serialize(text),
WPCordovaClassLib.Cordova.JSON.JsonHelper.Serialize(url));
>     string callback = @"(function(code, text, url){
> 	try {
> 	    window.__onXHRLocalCallback[ url ].call(null, code, text);
> 	}
> 	catch(e) {
> 	    console.log('Error calling method from XHRHelper :: ' + e);
> 	}
>     })" + args;
>     Browser.InvokeScript("eval", new string[] { callback });
> }
> {code}
> To be called as {{InvokeCallback(url, 200, text);}} or {{InvokeCallback(url, 404, null);}}
> Thanks.



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