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Date: Thu, 23 Aug 2012 01:53:42 +1100 (NCT)
From: "Andrew Grieve (JIRA)" <jira@apache.org>
To: callback-dev@incubator.apache.org
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Subject: [jira] [Commented] (CB-638) Slow native bridge (especially android)
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    [ https://issues.apache.org/jira/browse/CB-638?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13439582#comment-13439582 ] 

Andrew Grieve commented on CB-638:
----------------------------------

I've checked in the first round of changes for this. Modes can be tested in the mobile-spec exec() benchmark.

    jsToNativeModes = {
        PROMPT: 0,
        JS_OBJECT: 1,
        LOCATION_CHANGE: 2  // Not yet implemented
    },
    nativeToJsModes = {
        // Polls for messages using the prompt() bridge.
        POLLING: 0,
        // Does an XHR to a local server, which will send back messages. This is
        // broken on ICS when a proxy server is configured.
        HANGING_GET: 1,
        // For LOAD_URL to be viable, it would need to have a work-around for
        // the bug where the soft-keyboard gets dismissed when a message is sent.
        LOAD_URL: 2,
        // For the ONLINE_EVENT to be viable, it would need to intercept all event
        // listeners (both through addEventListener and window.ononline) as well
        // as set the navigator property itself.
        ONLINE_EVENT: 3,
        // Uses reflection to access private APIs of the WebView that can send JS
        // to be executed.
        // Requires Android 3.2.4 or above.
        PRIVATE_API: 4
    };


-I've not implemented the any keyboard work-arounds for LOAD_URL
-I've not added a workaround for hiding online/offline events from changing
-JS_OBJECT probably needs a better enable/disable detection. Right now it's disabled only for the 2.3 emulator instead of checking for JSC (via http://stackoverflow.com/questions/6768474/how-can-i-detect-which-javascript-engine-v8-or-jsc-is-used-at-runtime-in-andro)

Some initial benchmark results from my Galaxy Nexus (echos per second, bigger is better, payload size=500 bytes):

Sync JS->Native:
PROMPT: 570
JS_OBJECT: 800

Using JS_OBJECT for JS->Native and async Native->Response:
Native->JS POLLING+PROMPT: 100
Native->JS HANGING_GET: 75-90
Native->JS LOAD_URL: 160
Native->JS ONLINE_EVENT+PROMPT: 200-270
Native->JS PRIVATE_API: 340

ONLINE_EVENT being faster than LOAD_URL surprised me. Especially since it can be made even a bit faster if it uses JS_OBJECT to retrieve the message instead of PROMPT.

Still to do:
-Implement LOCATION_CHANGE JS->Native mode
-Add detection logic for JS_OBJECT support (this will involve loading a test page to run some JS)
-Add hiding of ONLINE_EVENTS changes from the app via cordova.addWindowEventHandler() and navigator.__defineGetter__('onLine', ...)
-Make POLLING and ONLINE_EVENT be able to use JS_OBJECT instead of always PROMPT.
-Make POLLING & HANGING_GET retrieve all pending messages in one call instead of one at a time
-Add mobile-spec test that ensures all modes work (when expected to)


Final Steps:
-Discuss changing the default bridge mode, as well as how to implement fall-back modes.
                
> Slow native bridge (especially android)
> ---------------------------------------
>
>                 Key: CB-638
>                 URL: https://issues.apache.org/jira/browse/CB-638
>             Project: Apache Cordova
>          Issue Type: Improvement
>          Components: Android
>            Reporter: Lee Crossley
>            Assignee: Andrew Grieve
>            Priority: Critical
>              Labels: 2.1.0
>
> Doing many native callbacks (such as writing files) has a significant overhead.
> Trigger.io's native bridge is more than 5 times faster than Cordova (on Android). http://trigger.io/cross-platform-application-development-blog/wp-content/uploads/2012/02/chart_1-21.png
> I'd love to see similar performance stats in Cordova.

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