andriod - technical review
TRANSCRIPT
Technical Review
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Mobile Platforms
There a lot of mobile platforms SymbianOS IPhoneOS BlackberryOS WinMo ALP OpenMoko WebOS Android BadaOS
Mobile Platform requirements Stable real-time kernel Steady HAL Power management Rich system libraries Rich application
framework Essential applications Steady UI Optimized application
management
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Introduction Another Mobile Platform
Offers Operating System
Kernel: Linux 2.6 Sys Library: Subset of LibC, LibM,
A complete application stack User land applications Development infrastructure
SDK 2.0.1 Java
NDK 1.5 C/C++
Components reusability and integration Based on ARM based processor
Can be run on x86 platform
(Cont.) Introduction License
Open source from the beginning Apache License
Made available Primarily for
Cell (mobile) devices But can also be use on
MIDs Nettops Mobile gaming devices Other light weight devices
Releases 1.5 – Cupcake 1.6 – Donut 2.0 – Eclair
2.1 – Extension to Eclair
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Support
Full multimedia hardware and software stack Advanced application supports
Background services Complex widgets Easy and manageable lifecycle Full control of the hardware through well designed
APIs
Advanced I/O supports
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History July 2005
Google acquired Android Inc. November 2007
OHA, Open Handset Alliance, consortium started with Texas Instruments, Broadcom Corporation, Google, HTC, Intel, LG, Marvell
Technology Group, Motorola, Nvidia, Qualcomm, Samsung Electronics, Sprint Nextel, T-Mobile
October 2008 First Android phone release – HTC Dream
December 2008 OHA, Open Handset Alliance, expanded with
ARM Holdings, Atheros Communications, Asustek Computer Inc, Garmin Ltd., Softbank, Sony Ericsson, Toshiba Corp, Vodafone Group
January 2010 OHA, Open Handset Alliance, expanded with
China Mobile Comm Corp., China Telecomm Corp., China United Network Comm., KDDI Corp., NTT DoCoMo Inc., Bouygues Telecom, etc
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Open Handset Alliance
The Kernel Kernel – Linux 2.6
Patches – Android Ashmem, binder, and Android Power Management (PM)
OS HAL Provides management for
Memory modules (Primary, Secondary) Processes
Provides networking stack Full TCP/IP v4 support
Provides device drivers Telephony, GSM, CDMA, GPRS, Edge, 3G, WiFi, Bluetooth, others
transceivers Accelerometer, gyroscope , GPS transceiver, magnetometer Touchscreen, keyboard, keypad, camera VGA display Others
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Native System Libraries C/C++ libraries
Interface through Java layer Includes …
1. Standard UNIX libc libraries Called BIONIC Derived from BSD Only on ARM and x86 platforms
1. Surface manager2. 3D graphics with/without H/W acceleration using OpenGL ES3. 2D scalable vector graphics using SGL (Skia)4. TrueType fonts5. Media frameworks including audio, video codecs6. HTTP rendering engine – Webkit7. Light database management through SQLite38. TCP socket security through SSL
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Java Runtime
Specialized Virtual Machine Dalvik Virtual Machine
Written by Dan Bornstein Architecture - Register-based machine Class files - Delvik Executibles .dex files
Structures ? Difference from normal class files Light weight, compact, and processor and memory efficient An uncompressed .dex size is less than compressed .jar Can contain several classes Code reordering and re-organization at installation time
Designed to enable execution of multiple instances
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(Cont.) Java Runtime
Relies on Linux for underlying functionality such as multi-threading and low level memory management
The dx utility No official JIT compiler
Core library – Java 1.5 SDK Completely not compatible with Java SE and ME
class library profiles E.g., J2ME, AWT, Swing are not supported
Subset of the Apache Harmony
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Dalvik Virtual Machine Motivation
Can run on lesser RAM Can run on slower CPUs Can run without swap space defined Can run with less power Can enable concurrent execution of multiple instances
Memory efficiency More memory requirement
Each application runs in its own address space – process Optimization
Shared constant pool in .dex files Minimal repetition Per type pools (implicit typing) Implicit labeling
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(Cont.) Dalvik Virtual Machine
Emphasis to use clean (shared/private) memory Emphasis to limit the use of dirty private memory
Memory types Clean memories
Common .dex files (shared) Application specific .dex files (private)
Private dirty memories Application “live” .dex structures Application heap
Shared dirty memories Common “live” .dex structures Shared COW heap
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(Cont.) Dalvik Virtual Machine Separate Garbage Collection meta
Specialized GC meta structures Optimized for memory usage with less fragmentation and sharing Each application heap is GCed independently
Run time efficiency Install time verification
Static type and reference checking, indices and offset checking Reduces run-time cost of checking the code
Install time optimization Byte swapping and padding Static linking Inlining special native methods Pruning empty methods Adding auxiliary data Creating shared constant pools
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(Cont.) Dalvik Virtual Machine
Why To avoid instruction dispatch Avoid unnecessary memory accesses Consume instruction stream efficiently
Higher semantic density per instruction
Uses register based interpreter Stacks are used to keep tracks on the methods nesting and
calling sequence
Efficient initialization and management of array data
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Enter the Zygote
The first process Similar to UNIX init process
Preloads and preinitializes shared classes Create clean shared memories Create dirty shared memories
Uses UNIX fork() to start a new application Provides shared mapping to the child
processes for shared classes Promotes the sharing of common code
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Application Framework All Java Libraries
1. Activity manager – Manages application life cycle An activity is an application UI window Activities are managed through system’s activity stack Four states of activity
Foreground – top on activity stack Paused – when lost focus, and still showing (partially) on the screen. Stopped – When completely hidden by another activity Killed - Killing the process
1. Package manager – Installed software manager2. Window manager – Manages UI components along with
screens and transitions3. Telephony manager – Provides the interface to the underneath
telephony/GSM services
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(Cont.) Application Framework
5. Resource manager – Provides access to the non-code components such as images, icons, audio/video, string tables, etc.
6. Content manager – Mediates in the data sharing among applications, such as contacts are shared to other application.
Various content providers Can access others, and publish own Content provider security
5. Location manager – Provides intends on registered location. Uses GPS, or GSM tower ID or WiFi location beacons to determine location.
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(Cont.) Application Framework
8. View system – Provides widgets to the application to create activities
Two new views; MapView and WebView
8. Notification manager – Enables the application to show custom alerts on the status bar.
9. XMPP services – Peer-to-peer Android device communication layer
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Applications
Java applications Runs in separate user address space - process Each is managed by its own DVM instance Can be replaced Can be installed from
Online app stores
Usually end up in calling native code that might goes to the kernel system call
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Security & Access Control Only Java applications can be installed Each application runs in its process under DVM Each process (DVM) is a sandbox Each application has its own UIDs and GIDs Additional access control on several operations
Architecture: No application by default has permission to perform any operation that would
adversely impact other applications, operating system, or the user. Such as
R/W on user’s private data; contacts R/W on another application data files Performing network (through GPRS/Edge, Wifi), bluetooth access, or Keeping the device awake
Application certificate, UID/GID, Access Control and URI Permissions
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(Cont.) Security & Access Control Application signing and certification
Contains authors identification, and signing authority
Access control The sandbox is executed with some permissions (access control) to the
operations. These access control permissions are defined in the application package, Set at installation point, and Can be modified by user when OS prompt for the permission to perform the
operation
UIDs and GIDs Each application and its components are installed with unique UID
Limits the applications to access Shared UIDs
Only allow applications with identical digital signature Each file created has the creator’s UID
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(Cont.) Security & Access Control URI permissions
Mainly for content providers Allows capability like access control Enables applications to manage other application’s accesses on their shared
contents
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OS Concerns Kernel
No udev support Static hardware linking and policy
No dynamic hotplug control and management Replaced by Vold
Provides static hotplug events processing Storage devices are not managed by HAL (VFS)
Replaced by Vold Responsible of mounting and unmounting of MMC subsystem
device Hardcoded power-management policy
Layered PM design Android PM mapped on Linux PM module To change the Android PM policy requires code change
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(Cont.) OS Concerns
Limited, un-natural (non-Linux style) I/O support Un-orthodox touchscreen support
No official support through tslib
Fixed sized framebuffer No support for larger resolution > 1024x768
Static hardware support assumptions Telephony (3G signal indicator hardcoded) Wifi (signal indicator hardcoded) Ringer volume slider assumes telephony present
No official Ethernet support
No X Window System supportwww.folio3.com
(Cont.) OS Concerns
LibC - Bionic No glibc support Only available on ARM and x86 platforms Partial pthreads support No SysV IPC support Limited C++ support
No STL support
No Linux headers Limiting the development of native binaries
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Application Development Online official guide
http://developer.android.com/guide/index.html
Development with Eclipse Using ADT plugin
Tools Android – To create/update projects Emulator – Qemu based ARM emulation system Debugger bridge – To interface with the emulator Ant – To compile and build projects into .apk files Keytool – To maintain keystore and private keys Jarsigner – To sign .apk files with private keys
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(Cont.) Application Development
Requires to learn the following skills1. Java programming language
2. Java 1.5 SDK library
3. Android application life cycle
4. Android APIs
5. Mobile HPC programming
6. Use of sensory hardware and Internet services
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(Cont.) Application Development
Native Development (NDK) http://developer.android.com/sdk/ndk
Java Vs. Native development
Why native development is required? Situations
Resource intensive work Complex algorithms Hardware interactions …
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Limitations Kernel
Limited support for Mass Storage Devices No official support for mouse, Ethernet devices No support of other filesystems, and hardware Very thin network protocol stack
System libraries No support for IPC among the application
Replaced by content manager Limited pthread support Limited UNIX/Linux native library support
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(Cont.) Limitations
Application Applications can only be installed on the primary nonvolatile
memory Most of the Linux binaries will failed to run on Android Only Java based application can be executed
Native code can be only packaged as library modules for the Java application
No compatibility to the Jave ME and SE platforms No Enterprise integration solutions
Missing push messaging or notifications
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Comparison With Other Mobile Platforms
IPhone Blackberry Android
Background application
Multiprocessing
Peer-to-peer communication
Extensible & Scalable in HW support
Platform support
Application development & publishing
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Comparison With Other Mobile Platforms
IPhone Blackberry Android
Third party community support
Enterprise integration
Multimedia support
Optimized Java support
Native development
Security
Organization Support
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Future of Android
IS VERY BIG
Increasing support for more hardware and platforms Extensions to more system level libraries Extensions to more Java runtime libraries Enterprise level support Increase in platform domain from cellphone market
to military, gaming, medical, and other domains And more …
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Conclusion It uses Linux, but loses all the flexibility of Linux Based on the assumption of hardware support available on the
smart-phones with no/limited flexibility for dynamic adjustments Requires custom work and patching to enable Android to run on
other non-mobile platform and/or with more hardware Provides native development, but disallows the creation,
execution of the native applications Provides easy application development using Java Provides rich application stack and multimedia support Backed by a stronger organization Google
Technically more stronger and mature platform than other mobile OS platforms such as IPhoneOS, Blackberry OS and WinMo
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