Introduction to Android OS - Touch Tour Chennai

Intoduction to Android OS 15 Oct 2011

TouchTour 2011 1

Introduction to Android

PRASANNAN.NANDROID CONSULTANT

Twitter : @tryprasannan

What is Android ?

� “Android is a complete set of software for mobile

devices, including an operating system, a middle-ware

and key mobile applications” (Google)

� It was initially developed by Android Inc.

(a firm later purchased by Google)

Oct 2011 2Intro to Android OS @ Touch Tour 2011 by Prasannan.N (@tryprasannan)


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Android - Overview

� First SDK : Nov 2007 & First Device : Oct 2008

� Technologically, Android includes middleware and

key/core applications, and uses a modified version of

the Linux kernel

� Allows developers to write managed code in Java

� Android Java = Java SE – AWT + Android API


Android Versions



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Version Name Kernel Release

1.1 - - 9 February 2009

1.5 Cupcake 2.6.27 30 April 2009

1.6 Donut 2.6.29 15 September 2009

2.0/2.1 Eclair 2.6.29 26 October 2009

2.2 Froyo 2.6.32 20 May 2010

2.3.x Gingerbread 2.6.35 6 December 2010

3.x Honeycomb 2.6.36 22 February 2011

Android Versions


Current DistributionPlatform API Level Distribution

Android 1.5 3 1.1 %

Android 1.6 4 1.4 %

Android 2.1 7 11.7 %

Android 2.2 8 45.3 %

Android 2.3 -

Android 2.3.2

9 0.5 %

Android 2.3.3 -

Android 2.3.4

10 38.2 %

Android 3.0 11 0.2 %

Data as on 3rd October 2011 found at http://developer.android.com/resources/dashboard/platform-versions.html



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Android Components

• Components

• Intents

• Lifecycle

• Manifest

• Processes


Components• 1 Application => N Components

• Applications can use components of other

applications

• Application processes lifecycle are managed by the

system

• N entry points, !1, and !main()



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Components

• Activities

• Services

• Broadcast Receivers

• Content Providers


Intents• Intent = asynchronous messaging system

• Components interact with each other via intents

• May/may not have a designated target

• Intents’ “payload” held in Intent Object

• Intent Filters are specified in special XML file called

“Android Manifest”



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Component Lifecycle

• Android automagically starts/stops/kills processes

• Entire system behaviour predicated based on low

memory

• System triggers Lifecycle callback methods when

relevant


Manifest

• Registry of all the application components

• XML format

• Always called “AndroidManifest.xml”

• Activity = <activity> ... Static

• Service = <service> ... Static

• Broadcast Receiver:

• Static = <receiver>

• Dynamic = Context.registerReceiver()

• Content Provider = <provider> ... static



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Processes

• Default: all callbacks to any app Component are

issued to the main process thread

• <activity>—<service>—<reeiver>—<provider> have

process attribute to override default

• Do NOT perform blocking/long operations in main

process thread:

– Spawn threads instead

• Process termination/restart is at system’s discretion


Development Tools

• Eclipse + ADT Plugin (+ JDK v5 or later)

• SDK & Tools:

• android – manage AVDs and SDK components

• apkbuilder- creating .apk packages

• dx- recompile java class files to dalvik executable

• adb – debug bridge

• emulator – QEMU-based ARM emulator

• ...



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Android Architecture

• fs,df.sdf,a


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Linux Kernel

� Android relies on Linux Kernel version 2.6 for core system

services such as

� Security

� Memory Management

� Process Management

� Network Stack, and

� Driver Model


Linux Kernel� The kernel acts as an abstraction layer between the

hardware and the rest of the software stack

� Android is built on the Linux kernel, but Android is not

Linux

– No native windowing system

– No glibc support

– Does not include the full set of standard Linux utilities

� Patch of “kernel enhancements” to support Android



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Why Linux Kernel?

� Great memory and process management

� Permissions-based security model

� Proven driver model

� Support for shared libraries

� Open source


Kernel Enhancements� Alarm

� Ashmem

� Binder

� Power Management

� Low Memory Killer

� Kernel Debugger

� Logger



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Native Libraries

� Android includes a set of C/C++ libraries used by various

components of the Android system.

� These capabilities are exposed to developers through the

Android application framework.

� Bionic - System C library

– super fast, small

– BSD-derived implementation of the standard C system library

(libc)

– Optimised for embedded Linux-based devices


Function Libraries - WebKit� WebKit

– Based on open source WebKit browser framework

– Customized by OS vendor

– Can render pages in full(desktop) view

– Full CSS, Javascript, DOM, AJAX support

– Support for single-column and adaptive view rendering



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Function Libraries – Media Framework

� Media Framework

– Based on PacketVideo OpenCORE platform

– Supports standard video, audio, still-frame formats

– Support for hardware / software codec plug-ins


Function Libraries – SQLite

� SQLite

– Light-weight transactional data store

– Back end for most platform data storage



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Native Servers – Surface Flinger� Surface Flinger


Native Servers – Surface Flinger� Surface Flinger



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Native Servers – Surface Flinger

� Provides system-wide surface “composer”, handling all surface

rendering to frame buffer device

� Can combine 2D and 3D surfaces and surfaces from multiple

applications

� Surfaces passed as buffers


Native Servers – Audio Flinger



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� Audio Flinger

– Manages all audio output devices

– Processes multiple audio streams into PCM audio out paths

– Handles audio routing to various outputs



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Android Runtime

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Android Runtime - Dalvik Virtual Machine

� Every Android application runs in its own process.

� Each one has its own instance of the Dalvik virtual machine.



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Dalvik• Oracle Java =

Java language + JVM

+ JDK libs

• Android Java =

Java language

+ Dalvik VM

+ Apache Harmony

• Supports JIT from v2.2 onwards (85% devices)


dex - Dalvik Executable

• JVM runs “.class” files

• Dalvik runs “.dex” files

• dex file => .class files post-processed by “dx” utility

• Uncompressed .dex = 0.5 * Uncompressed .jar

• Odex = Optimised dex (specific to hw platform)



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Android Runtime - Dalvik VM� Run on a relatively slower CPU with relatively less RAM

� Run on a OS without swap-space

� Dalvik has been written so that a device can run multiple VMs

efficiently.

� The Dalvik VM executes files in the Dalvik Executable (.dex)

format.

� .dex is optimized for minimal memory footprint.



� The VM is register-based, and runs classes compiled by a Java

language compiler.

� Java classes are transformed into the .dex format by the included

"dx" tool.

� Dalvik relies on the Linux kernel for threading and low-level

memory management.



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� Android’s custom clean-room implementation virtual

machine

� Provides application portability and runtime consistency

� Runs optimized file format (.dex) and Dalvik bytecode

� Java .class / .jar files converted to .dex at build time



�Designed for embedded environment

� Supports multiple VM processes per device

� Highly CPU-optimized bytecode interpreter

� Uses runtime memory very efficiently



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Android OS Startup

39

Startup Sequence• Bootloader

• Linux Kernel

• Init

• Daemons

• Zygote

• System Server

• Activity Manager

• Launcher + Home



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OS Start-up Walkthrough

� It all starts with init…

� Similar to most Linux-based systems at startup

� The bootloader loads the Linux kernel and starts the init

process.


OS Start-up Walkthrough� Init starts Linux daemons, including:

– USB Daemon (usbd) to manage USB connections

– Android Debug Bridge (adbd) to manage ADB connections

– Debugger Daemon (debuggerd) to manage debug processes requests (dump memory,

etc.)

– Radio Interface Layer Daemon (rild) to manage communication with the radio



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� Init process starts the zygote process

– A nascent process which initializes a Dalvik VM instance

– Loads classes and listens on socket for requests to spawn VMs

– Forks on request to create VM instances for managed processes

– Copy-on-write to maximize re-use and minimize footprint


OS Start-up Walkthrough� Init starts runtime process:

– Initializes Service Manager – the context manager for Binder that

handles service registration and lookup

– Registers Service Manager as default context manager for Binder

services



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� Runtime process sends request for Zygote to start System

Server

– Zygote forks a new VM instance for the System Service process

and starts the service


OS Start-up Walkthrough� System Service starts the native system servers, including:

– Surface Flinger

– Audio Flinger



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� Native system servers register with Service Manager as IPC

service targets:



� System Service starts the Android managed services:



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� Android managed Services register with Service Manager:





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� After system server loads all services, the system is ready…





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OS Start-up Walkthrough� Each subsequent application is launched in its own process


OS Layer Interaction



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OS Layer Interaction

� 3 Main Android layer interaction types

� Direct

– App > Runtime Service > lib

� via Native Service

– App > Runtime Service > Native Service > lib

� via Native Daemon

– App > Runtime Service > Native Daemon > lib


App > Runtime Service > lib



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App > Runtime Service > lib


App > Runtime Service > Native Service > lib



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App > Runtime Service > Native Service > lib


App > Runtime Service > Native Daemon > lib



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App > Runtime Service > Native Daemon > lib


Queries ?


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Thank You.


Technology

Introduction to Android OS - Touch Tour Chennai