An Empirical Study of Android Alarm Usage for Application Scheduling

Mario Almeida1, Muhammad Bilal1Jeremy Blackburn2, Konstantina Papagiannaki2

1 Polytechnic University of Catalonia2 Telefonica Research

1 (4knahs@gmail.com)

Energy: Major Concern for Mobiles

● Main Culprits?○ Screen○ Radio○ CPU○ Graphics○ Sensors

● Interactive Use● Background Use

(ACM ID 1855861 USENIXATC'10)

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How Much Background Use Is There?

Online presence apps tend to run in background 70-80% of the time!

(Andrius et al CONEXT’13)

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How Much Background Use Is There?

Up to 9 times faster energy drain with 4 popular apps!

(Andrius et al CONEXT’13)

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How To Schedule Background Tasks?

Android alarms to the rescue!

Time critical (exact) or not (inexact/deferrable)

Apps can determine:

● Deferrability● Trigger time● Repetition interval of alarms!

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How To Schedule Background Tasks?

From Android Kitkat (19) alarms can be batched!

● Reduced wakeups● Saves energy (data)

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Major target of energy saving innovation in last 2 Google IO conferences!

Traffic shaping (e.g., batching) cannot ignore app-protocol interaction & OS integration

*Vergara et al IWCMC’13

How To Schedule Background Tasks?

Android 6 (SDK23 ,Oct 15) -> 3 new APIsJobInfo APIs (21) not adopted by apps

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How To Schedule Background Tasks?

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Android Studio

Eclipse

How To Schedule Background Tasks?

Android 6 (SDK23 ,Oct 15) -> 3 new APIsJobInfo APIs (21) not adopted by apps

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API Fragmentation leads to unpredictable QoS/performance

Questions

● How outdated are target SDKs?● How widespread is alarm usage?● How do apps use alarms?● How do alarms impact a running device?● How to improve alarm usage?

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Dataset & Methodology

● Google Play Store Crawler○ Up to 564 of the most popular free apps for each

app category○ >22K unique apps

● Popular apps○ + representative apps on user devices○ + likely -> optimized for energy consumption

> 81% of total downloads!

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May 2015

*Viennot et al SIGMETRICS’14

Dataset & Methodology

Static analysis:

○ Alarm API usage○ Annotations (e.g., TargetApi)○ Package names○ Target SDKs

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Skype

How Outdated Are Target SDKs?

Majority (76%)18 months.(SDK<=19).

~Half lagging by > 21 months!

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How Widespread Is Alarm Usage?

Most Alarms Exact Alarms

Widgets (80%) Casino games (37.9%)

Wallpapers (63%) Weather (35%)

Personalization (60%) Family games (32.5%)

Communication(59%) Communication (32.1%)

47% of apps use alarms

Apps define up to 70 alarm!

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Why Are Alarms So Widespread?

10% of ALL alarms are defined in these libraries

22% are exact!

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How Do Apps Use Alarms?

31.5% of all alarms are repeating!

*Note: apps can have both exact and inexact alarms!

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SDK < 19

Alarm Type Percentage of Apps

Inexact Alarms 8.49%

Exact Alarm 44.05%

Any Alarm 46.06%

SDK >= 19

Alarm Type Percentage of Apps

Inexact Alarms 52.91%

Exact Alarm 2.31%

Any Alarm 53.49%

Is It That Many Apps Are Outdated?

Even regularly updated apps often do not update their

SDK!17

How Do Alarms Impact A Running Device?

Experiment:

● Install dataset apps on freshly flashed device● Run them once and let them on for 30m● Reboot, let the phone go idle, wait 30m● Record alarm definitions/wake ups for 3h

We used a device with Android 4.4.4 (SDK 19) with alarm batching capabilities!

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How Do Alarms Impact A Running Device?

Dataset 1:

● 30 most popular apps○ >1K to >500M downloads

Dataset 2:

● 30 apps with most setRepeating alarms and SDK <19 ○ deferred if SDK>= 19

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How Frequent Are Device Wakeups?

Not deferred due to SDK target!

High correlation (r=0.86, p<0.01) alarm registered <-> wakeups

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Dataset 1:

● 261 alarms registered, 20% woke the device

Dataset 2:

● 1041 alarms registered, 61% woke device!

Examples Of Careless Alarm Usage

● Norton Security & Antivirus○ Both SDK 17, 10M-50M downloads, together

woke the device 141 times!● Spoora (instant messaging)

○ SDK 9, 10-50K downloads, woke the device 372 times!

● Facebook app & messenger○ Do not share communication, both do keep-alives

and woke the device 47 times!

Repeated & SDK < 19 Most popular apps

com.spoora (SDK 9, woke 372) com.facebook.orca (24)

com.symantec.mobilesecurity (SDK 17,131)

com.facebook.katana (23)

com.pad.comicsisland.activity (55)

com.cleanmaster.security (1)

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How To Improve Alarm Usage?

● Improve dev knowledge?○ What about API fragmentation?

● Make all alarms inexact?○ Does it break?

● Simply target a newer SDK?○ Might work for more recent devices

● iOS?○ Are alarms really needed?

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Summary

● ~ 50% apps define alarms, from which ~40% have exact alarms.

● Alarms & API fragmentation can greatly affect energy efficiency.

● Most alarms use APIs outdated by >18months.● Alarms:

○ Present in all categories.○ Up to 70 alarm definitions per app.○ At least 10% due to 3rd party libs.○ Can wake the device very often -> wrong SDK 23

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Thank You For Your Time!

Questions?

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News prior to study!

Doze:

● Android 6 -> SDK 23 (study is <= 22).● Long period of inactivity -> defer alarms● setExact() and setWindow() -> deferred● BUT:

○ 3 new apis (setAndAllowWhileIdle, setExactAndAllowWhileIdle and setAlarmClock)

○ Better name semantics, devs can still misuse!

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Image rights

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