[jira] [Updated] (CB-3901) Backlog of Acceleration messages are received after plugin/sensor is stopped

["Bas Bosman (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CB-3901?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Bas Bosman updated CB-3901:
---------------------------

    Component/s: Plugin Geolocation

> Backlog of Acceleration messages are received after plugin/sensor is stopped
> ----------------------------------------------------------------------------
>
>                 Key: CB-3901
>                 URL: https://issues.apache.org/jira/browse/CB-3901
>             Project: Apache Cordova
>          Issue Type: Improvement
>          Components: Android, CordovaJS, Plugin Geolocation
>    Affects Versions: 2.7.0
>            Reporter: Peter
>            Assignee: Joe Bowser
>            Priority: Minor
>
> There is a kind of race condition between the Accelerometer events being generated and the processing of the Cordova bridge messages.
> For example:
> In the plugin:
> * Accelerometer events are generated at a rapid rate.
> * The event always results in data transfer across the bridge. e.g. onSensorChanged calls this.win() calls sendPluginResult…
> * So very quickly lots of PluginResult messages will be queued, requiring processing
> Meanwhile in the JavaScript:
> * callbackFromNative handles the incoming messages and if there are any listeners then it deals with the acceleration event.
> * When it determines there are no user listeners left then a sensor “stop” will be issued 
> But even after the “stop” is executed, there is still a potentially large backlog of queued acceleration messages still remaining to be processed. 
> Since there are no user listeners left the user does not get to see them – they so just end up going nowhere.
> I don’t know whether there is anything possible that can be done about this (it seems to be just the way it is designed) but perhaps there should be some comment in the code for the accelerometer callbacks to describe how they may be called even though all user listeners have been removed. And maybe the success function can be modified to not bother constructing the Acceleration instance unless it will be used. Something like this?
> BEFORE:
> {code}
> function(a) {
>    var tempListeners = listeners.slice(0);
>    accel = new Acceleration(a.x, a.y, a.z, a.timestamp);
>    for (var i = 0, l = tempListeners.length; i < l; i++) {
>        tempListeners[i].win(accel);
>    }
> }
> {code}
> AFTER:
> {code}
> function(a) {
>     // NB: It is possible for this callback to be executed even after the accelerometer 
>     // sensor is “stopped” due to a backlog of unprocessed acceleration messages.
>     var tempListeners = listeners.slice(0);
>     var nListeners = tempListeners.length;
>     if (nListeners > 0) {
>         accel = new Acceleration(a.x, a.y, a.z, a.timestamp);
>         for (var i = 0, l = nListeners; i < l; i++) {
>             tempListeners[i].win(accel);
>         }
>     }
> }
> {code}



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