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From "Joe Bowser (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CB-2963) Javascript callback functions are not executed in the correct order
Date Tue, 09 Apr 2013 18:42:17 GMT

    [ https://issues.apache.org/jira/browse/CB-2963?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13626931#comment-13626931
] 

Joe Bowser commented on CB-2963:
--------------------------------

[~davide] Do you have a test case that we can use to check this behaviour?  The setTimeout
call looks super hacky and I'm not sure this would work across all devices.
                
> Javascript callback functions are not executed in the correct order
> -------------------------------------------------------------------
>
>                 Key: CB-2963
>                 URL: https://issues.apache.org/jira/browse/CB-2963
>             Project: Apache Cordova
>          Issue Type: Bug
>          Components: Android
>    Affects Versions: 2.5.0
>            Reporter: Davide Maestroni
>            Assignee: Joe Bowser
>            Priority: Critical
>
> I created an application which sends asynchronous notifications from the native to the
Javascript side. I noticed that in some cases the Javascript code of the callbacks is not
executed in the expected order.
> Let me show an example:
> # a native event trigger a notification to the Javascript side where a callback function
(callback1 - part 1) gets correctly called
> # in the while, on the native side, a different notification is triggered
> # inside the Javascript code of the first callback the cordova.exec() API is issued
> # at this point the Javascript code of the second callback (callback2) is executed sequentially
on the same thread
> # when the second callback completes, the final part of the code in the first callback
(callback1 - part 2) is executed
> So that, if the callback functions are defined as below:
> {noformat}
> function callback1() {
>     <callback1 - part 1>
>     cordova.exec(...);
>     <callback1 - part 2>
> }
> function callback2() {
>     <callback2>
> }
> {noformat}
> the Javascript code gets executed in the following order:
> {noformat}
> <callback1 - part 1>
> cordova.exec(...);
> <callback2>
> <callback1 - part 2>
> {noformat}
> which is not the expected behavior.
> I believe the problem is related to the following lines of code in the _cordova.android.js_
file:
> {noformat}
>         var messages = nativeApiProvider.get().exec(service, action, callbackId, argsJson);
>         androidExec.processMessages(messages);
> {noformat}
> which get called if _jsToNativeBridgeMode == jsToNativeModes.JS_OBJECT_.
> That causes enqueued messages to get executed sequentially before the execution of the
first callback is complete.
> An easy fix would be to change the above code into:
> {noformat}
>         var messages = nativeApiProvider.get().exec(service, action, callbackId, argsJson);
>         setTimeout(function() {
>                 androidExec.processMessages(messages);
>         }, 0);
> {noformat}
> so that the enqueued messages are processed in the next Javascript loop.

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