1055939 - Use a proper sensor delay hint when registering sensors callbacks

Status: RESOLVED FIXED

(Firefox for Android Graveyard :: General, defect)

Description

[Mark Finkle (:mfinkle) (use needinfo?)]

Bug 733653 landed a change for some sensors that doesn't look right:
http://hg.mozilla.org/mozilla-central/rev/2aef3c754ff5
https://bugzilla.mozilla.org/show_bug.cgi?id=733653

We are basically changing:
-                sm.registerListener(GeckoApp.mAppContext, gOrientationSensor,   SensorManager.SENSOR_DELAY_GAME);
+                sm.registerListener(GeckoApp.mAppContext, gOrientationSensor,   sDefaultSensorHint);

We assumed that "registerListener" takes a value in milliseconds and we used sDefaultSensorHint set to 100. But "registerListener" uses microseconds:
http://developer.android.com/reference/android/hardware/SensorManager.html#registerListener%28android.hardware.SensorEventListener,%20android.hardware.Sensor,%20int%29

Android docs say that SENSOR_DELAY_NORMAL is 200,000 microseconds. SENSOR_DELAY_GAME is 20,000 microseconds.
http://developer.android.com/guide/topics/sensors/sensors_overview.html

If we really want 100 milliseconds, we should change sDefaultSensorHint to 100000. However, I see the docs say some conflicting information about using the named constants (SENSOR_DELAY_XXX) and passing a custom delay, like sDefaultSensorHint. One doc says custom delays are Android 2.3 (API 9) and higher. The other doc says Android 3.0 (API 11).

To play it safe, I think we should use SENSOR_DELAY_GAME, which is 60 milliseconds or ~17 Hz.

Comment 1

[Mark Finkle (:mfinkle) (use needinfo?)]

Attachment: limit-sensors v0.1

Note that the Android docs don't say that the hint is strictly enforced and that sensor changes can still happen faster than the hint.

We still might want a new bug to add real throttling so we can lower power consumption.

Comment 2

[Mark Finkle (:mfinkle) (use needinfo?)]

https://tbpl.mozilla.org/?tree=Try&rev=e9646c563525

Comment 3

[Mark Finkle (:mfinkle) (use needinfo?)]

Try run looks fine. The testRetrictedProfiles issue is from a different patch.

https://hg.mozilla.org/integration/fx-team/rev/30c1ec16554a

Comment 4

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/30c1ec16554a

Comment 6

[Chris Peterson [:cpeterson]]

(In reply to Mark Finkle (:mfinkle) from comment #0)
> SENSOR_DELAY_GAME is 20,000 microseconds.
> ...
> To play it safe, I think we should use SENSOR_DELAY_GAME, which is 60
> milliseconds or ~17 Hz.

btw, if SENSOR_DELAY_GAME is 20,000 microseconds, then its sampling rate is 50 Hz, not 17 Hz. Bug 1085789 links to a research paper (about using the device's gyroscope as a side channel to record speech) which unknon stumbled upon the Fennec bug fixed here. The paper says Chrome on Android's sampling rate is 25 Hz and Safari on iOS's is 20 Hz. So Fennec's 50 Hz may be overachieving here because web content will be designed to work with these 20–25 Hz browsers. :)