Disclaimer: The contents in this document are only my personal opinions, do not reflect the opinions of my employer or anyone else.

Transcription

1 Disclaimer: The contents in this document are only my personal opinions, do not reflect the opinions of my employer or anyone else. Android overview From a system design perspective Xiao-Feng Li xiaofeng.li@gmail.com /9/21 Android Overview - Xiao-Feng Li 1

2 Android overview From a system design perspective PART I Design principles 2012/9/21 Android Overview - Xiao-Feng Li 2

3 Question 1 Q: What do you expect from a mobile phone? 2012/9/21 Android Overview - Xiao-Feng Li 3

4 Answer To Q1 Q: What do you expect from a mobile phone? A: (no correct answer, but reasonable answer) Easy communications Long battery life Fast boot-up/shutdown Smooth operations Delicate industry design Applications Could be a close environment 2012/9/21 Android Overview - Xiao-Feng Li 4

5 Question 2 Q: What do you expect from a smart-phone? 2012/9/21 Android Overview - Xiao-Feng Li 5

6 Answer To Q2 Q: What do you expect from a smart-phone? A: (no correct answer, but reasonable answer) All of those features with a mobile phone, plus PC features Programming environment Portal to Internet And security risks Gaming station features Sensors, 3D Must be an open environment 2012/9/21 Android Overview - Xiao-Feng Li 6

7 Question 3 Q: What build an open pleasant environment? 2012/9/21 Android Overview - Xiao-Feng Li 7

8 Answer To Q3 Q: What build an open pleasant environment? A: (no correct answer, but reasonable answer) Favorable APIs to developers Choices of applications to users Seamless access to Internet/Cloud services Pleasant user experience Maximize information flow 2012/9/21 Android Overview - Xiao-Feng Li 8

9 Question 4 Q: What prevent an open environment? 2012/9/21 Android Overview - Xiao-Feng Li 9

10 Answer To Q4 Q: What prevent an open environment? A: (no correct answer, but reasonable answer) Openness vs. Security User experience vs. Battery life Cloud readiness vs. Local computation Law of conservation of energy ITJ paper: Mobile OS Architecture Trends, Xiao-Feng Li, et. al. 16(4), /9/21 Android Overview - Xiao-Feng Li 10

11 Question 5 Q: What does Android do? APIs Applications Internet/Cloud Security User experience Battery life 2012/9/21 Android Overview - Xiao-Feng Li 11

12 Answer To Q5 Q: What does Android do? A: (no correct answer, but reasonable answer) APIs: SDK, NDK, RS, HTML/JS Applications: Google Play, web apps Internet/Cloud: Chrome/webview/HTML5 Security: Java, Permission, Linux security, sig User experience: touch, mem, perf Battery life: Linux PM, wake lock Feature list does not tell the truth 2012/9/21 Android Overview - Xiao-Feng Li 12

13 Question 6 Q: How does Android put them together? 2012/9/21 Android Overview - Xiao-Feng Li 13

14 Answer To Q6 Q: How does Android put them together? A: (no correct answer, but reasonable answer) 1. Java as the primary API language Top popularity is not without rationality 2. Application framework Service-oriented, component-based 3. Applications are wired into framework 4. Hardware abstraction layer (HAL) 5. Linux kernel Holistic design makes the cathedral 2012/9/21 Android Overview - Xiao-Feng Li 14

15 Android Stack Layers make the holistic design possible 2012/9/21 Android Overview - Xiao-Feng Li 15

16 Question 7 Q: What does a common OS distribution do? APIs Applications Internet/Cloud Security User experience Battery life 2012/9/21 Android Overview - Xiao-Feng Li 16

17 Answer To Q7 Q: What does a common Linux distro do? A: (no correct answer, but reasonable answer) APIs: open choices Applications: abundant Internet/Cloud: Mozilla Firefox, etc. Security: Linux security User experience: Gnome, KDE, etc. Battery life: Linux PM More features may not always excel 2012/9/21 Android Overview - Xiao-Feng Li 17

18 Question 8 Q: How does a common Linux distro put them together? 2012/9/21 Android Overview - Xiao-Feng Li 18

19 Answer to Q8 Q: How does a common Linux distro put them together? A: (no correct answer, but reasonable answer) APIs: open choices Applications: abundant Internet/Cloud: Mozilla Firefox, etc. Security: Linux security User experience: Gnome, KDE, etc. Battery life: Linux PM Bazar is still bazar 2012/9/21 Android Overview - Xiao-Feng Li 19

20 Question 9 Q: What does J2ME do? 2012/9/21 Android Overview - Xiao-Feng Li 20

21 Answer to Q9 Q: What does J2ME do? A: (no correct answer, but reasonable answer) APIs: roughly ok Applications: roughly ok Internet/Cloud: roughly ok Security: roughly ok User experience: roughly ok Battery life: roughly ok Roughly ok is not ok 2012/9/21 Android Overview - Xiao-Feng Li 21

22 Question 10 Q: How does J2ME put them together? 2012/9/21 Android Overview - Xiao-Feng Li 22

23 Answer to Q10 Q: How does J2ME put them together? A: (no correct answer, but reasonable answer) APIs: ok + OS Applications: ok + OS Internet/Cloud: ok + OS Security: ok + OS User experience: ok + OS Battery life: ok + OS Who are you, J2ME or OS? 2012/9/21 Android Overview - Xiao-Feng Li 23

24 Question 11 Q: What does Windows desktop do? A: (no correct answer, but reasonable answer) APIs Applications Internet/Cloud Security User experience Battery life 2012/9/21 Android Overview - Xiao-Feng Li 24

25 Answer to Q11 Q: What does Windows desktop do? A: (no correct answer, but reasonable answer) APIs: Win API in C++ Applications: abundant Internet/Cloud: IE Security: oops! User experience: (Not responding) Battery life: Time does not solve all problems 2012/9/21 Android Overview - Xiao-Feng Li 25

26 Question 12 Q: How does Windows put them together? 2012/9/21 Android Overview - Xiao-Feng Li 26

27 Answer to Q12 Q: How does Windows put them together? A: (no correct answer, but reasonable answer) Win API Kernel Time freezes at 80s 2012/9/21 Android Overview - Xiao-Feng Li 27

28 Windows Stack Services built on top of API 2012/9/21 Android Overview - Xiao-Feng Li 28

29 Bonus Slide: Windows 8 Stack Much better as a smartphone OS as I expected API built on top of services 2012/9/21 Android Overview - Xiao-Feng Li 29

30 Android Design Explained Complete, consistent, modular API: Full sets of high level APIs for all the tasks Apps: components to be wired into the system App framework: rich set of services/abstractions Security: every application is a Linux user User experience: mem/power/perf, smoothness/responsiveness 2012/9/21 Android Overview - Xiao-Feng Li 30

31 Android overview From a system design perspective PART II Runtime model 2012/9/21 Android Overview - Xiao-Feng Li 31

32 Android Application Not a standalone application, but components of the system 2012/9/21 Android Overview - Xiao-Feng Li 32

33 Activity Lifecycle Activity is integrated with Activity Manager Service through binder 2012/9/21 Android Overview - Xiao-Feng Li 33

34 Android Service Android is service-oriented design 2012/9/21 Android Overview - Xiao-Feng Li 34

35 Android Startup Launch all the system services 2012/9/21 Android Overview - Xiao-Feng Li 35

36 Android Running Sanboxed applications (and services) 2012/9/21 Android Overview - Xiao-Feng Li 36

37 Android Binder Core IPC mechanism that enables Android client/server modular design Like CORBA, but much simpler and more efficient Only for intra-os IPC AIDL to define the service interface (stub, proxy) Support both C++ and Java binding Linux kernel modified to support binder Also for IPC performance and security 2012/9/21 Android Overview - Xiao-Feng Li 37

38 Binder Running 2012/9/21 Android Overview - Xiao-Feng Li 38

39 Example: Alarm Service 2012/9/21 Android Overview - Xiao-Feng Li 39

40 Binder Threads Binder threads exist invisibly for IPC Binder threads created by system automatically 2012/9/21 Android Overview - Xiao-Feng Li 40

41 Android Application Structure Role of binder thread Activity main thread Message Handling Message queue Binder thread Post a message to main thread queue Incoming binder call Binder interface implementation 2012/9/21 Android Overview - Xiao-Feng Li 41

42 Binder Threads Running Binder #1: IApplicationThread Activity lifecycle transition callback is triggered by the incoming call on binder IApplicationThread, that was initiated by AM service. Binder #2: IWindow.stub UI events handling triggered by IWindow.stub binder calls 2012/9/21 Android Overview - Xiao-Feng Li 42

43 Start Activity (1/2) Activity thread IAppThread Activity Manager Service :startactivity (IAppThread..) Check permission, check if new task, change activities sequence, new activity record and queue it into stack startactivitylocked() Post msg :schedulepauseactivity () resumetopactivitylocked () startpausinglocked () Activity1.OnPause() :activitypaused() completepauselocked () Queue the activity into stopping list If target process is not present, call startprocesslocked() to create the process and exit. Following steps will be triggered by the binder call attach() that is first thing main thread does. resumetopactivitylocked () Post msg :schedulelaunchactivity () startspecificactivitylocked () realstartactivitylocked () 2012/9/21 Android Overview - Xiao-Feng Li 43

44 Start Activity (2/2) Activity thread IAppThread Activity Manager Service Activity2.OnCreate() Activity2.OnStart() Activity2.OnResume() activitypause() completeresumelocked () ensureactivitiesvisiblelocked () Activity stop transition is executed at idle time. TIMEOUT activityidleinternal () Get all activities in stopping list and no long visible Post msg Activity1.OnStop() :schedulestopactivity () :activitystopped () processstoppingactivitieslocked () stopactivitylocked() If the finish flag is set in the activity record (in scenario of calling finish), activitystopped() will continue the destroy transition. 2012/9/21 Android Overview - Xiao-Feng Li 44

45 Activities And Tasks (1/2) 2012/9/21 Android Overview - Xiao-Feng Li 45

46 Application A Activities And Tasks (1/2) Application A Activities Map Application B Activity Manager Service Activity Records Stack Activities Map 4 3 Task Stack T1 T2 2012/9/21 Android Overview - Xiao-Feng Li 46

47 Android overview From a system design perspective (Not yet put together here ) PART III Framework design 2012/9/21 Android Overview - Xiao-Feng Li 47

48 Summary Smartphone OS has to be open and elegant Comprehensive and consistent API Service oriented framework to back the API App components are wired into the framework HAL to hide hardware differences UID/process based security support to apps Traditional OS kernel for platform management 2012/9/21 Android Overview - Xiao-Feng Li 48

49 Acknowledgements Some of the figures are taken from materials of their respective owners 2012/9/21 Android Overview - Xiao-Feng Li 49