00 Android Overview

7/29/2019 00 Android Overview

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Android

InternalsDao Thanh Chung CSLab30/9/2011Email: [email protected]

Android Internals - @chung_sfc 1


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Rumors

10/2008 released Sales grew by nearly 900% from 2009 5/11 : 294.730 apps (vs iOS 381.062 apps)



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Agenda

1. What is Android?2. Android Stack3. Operating System Features



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1.What is Android?

A complete set of software for mobile devices:o An operating systemo Middlewaveo Key mobile applications

Openo No license feeso Great deal of Open Handset Alliance (OHA)

Fast & easy application development



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Open Handset Alliance (OHA)

A group of 84 techbology and mobile companieso Google, Samsung, HTC, Sharp, LG, Intel, etc

They together develop Androido The first complete, open, and free mobile platform

h`p://www.openhandsetalliance.com/index.html



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Why Open?


Industry

Users

Developer

Source availble after handsets ship Everyone can build a system image

Users control what gets installed

They choose thedefault se`ings

Can integrate, extend, and replace existingComponents No hidden or privilegedFramework APIs


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Agenda




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2.Android Stack


Android Stack is


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System Architecture



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Linux Kernel

Run on Linux 2.6.x modified Built on the Linux kernel, but Android is not Linux Linux kernel provides:

oHardware abstraction layer

o Memory managemento Process managemento Power managemento Binder Drivero Networking



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Native Libraries

Wri`en in C/C++ Some libraries

o Libc : c standard libo SSL : secure socket layero SGL : 2D image engineo SQLite : Embedded databaseo Webkit : Kernel of web brower



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Dalvik

Core librarieso Provides the functionality of JAVA

Dalvik VMo Java-based license free VMo Register-based (DalvikVM) vs Stack-based (JVM)o Optimized for low memory requiremento Runs .dex fileso Completely Fair Scheduler (CFS)

Red-Black Tree



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Application Framework

Wri`en in Java Some frameworks

o Activation manager controls the life cycle of the appo Content providers encapsulate data that is shared (e.g. contacts)o Location manager figures out the location of the phone (GPS,

GSM, WiFi)

o Notification manager for events such as arriving messages,appointments, etc



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Applications

Packaged into APK files 5/11 : 294.730 apps



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More details



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Android and Java



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3. Layer Interactions

Apps talk to native libraries 3 ways

o App Runtime Service Libo App Runtime Service Native Service Libo App Runtime Service Native Deamon Lib



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App Runtime Service Lib



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App Runtime Service Native Service Lib



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App Runtime Service Native Deamon Lib



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Agenda




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3. OS Features



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File System

Yet Another Flash File System (YAFFS) by defaulto Useful for NAND and NOR Flasho Boots quickly

3 main mount pointso One for systemo One for appso One for whatever

Each app has its own sandboxo /data/data/com.chung.helloworldo Easily accessible



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Security

Each App runs inside its own Linux process Each App has

o Its own file systemo Its own preferenceso Its own database

Other applications can not access any of its datao Unless shared



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Memory Management

Handled by the native Linux kernel How to use memory for each application

o Its own run time and virtual machine to manage applicationmemory

o Its run time also manages the process lifetimes Stops and kills processes as necessary to manage

resources



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Process States


Kill lower priority ifnecessary

Active Processo a process runs a activity

Visible Processo a process holds a paused

Started Service Processo a process started service

Background Processo an activity that is no longer

visible Empty Process

o a processe contains no activeapplication


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Power Management

Android supports its own Power Management Kernel modified to fulfill some special needs of certain

platformo MSM7xxx, Open Multimedia Application Platform (OMAP)

Apps and services request CPU resources with "wakelocks

If no active wake locks, Android will shut down the CPU



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Wake locks

Wake locks are used by applications and services torequest CPU resources

Wake locks exampleo Create a wake lock and specify the power management flags for

screen, timeout, etc.

o Acquire wake lock.o Perform operation (play MP3, open HTML page, etc.).o Release wake lock.



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Power Management



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Application Anatomy

An android application is based on four differentcomponentso Activity, Service, BroadcastReceiver and ContentProvider

Not necessarily consists of all four of these components At least an Activity in GUI



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Application Anatomy

Activityo Single screeno UI composed of views o Responds to eventso Change screens by starting new Activity

Serviceo Runs without UI (example: media player automatically)o Long-livedo Communicate with via interface exposed by service (example:pause, rewind, etc)



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Application Anatomy

BroadcastReceivero For reactions to an external event (phone rings, data network is

available, alarm)

ContentProvidero Share data with other apps



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Install Android SDK

SDK = Software Development Kit Download SDK:

o h`p://developer.android.com/sdk/index.html

Add platform and packageso h`p://developer.android.com/sdk/installing/adding-

packages.html

o Should download 2.3, 4.0 platform Install Eclipse and ADT plugin

o h`p://developer.android.com/sdk/installing/installing-adt.html Install suitable drivers for Android devices and Ge`ing

Started ^^

Android Internals - @chung sfc 33

Documents

00 Android Overview