ANDROID NATIVE APP: INTRODUCTION TO ANDROID. Roberto Beraldi

Transcription

1 ANDROID NATIVE APP: INTRODUCTION TO ANDROID Roberto Beraldi

2 Role of an operating system APPLICATIONS OPERATING SYSTEM CPU MEMORY DEVICES

3 Android = OS + Middleware Based on Linux Not just another distribution. There are important changes related to PROCESS MANAGEMENT MEMORY MANAGMENET IPC OS uses several Managers to take its decisions: Activity Manager Packeges Manager An Application runs inside a Process. An application is composed of smaller components, singularly managed (have a lifecycle )

4 Process Management in android Processes host applications Processes running applications are all created from the same process, called Zygote (not fork and exec as in linux, only fork) Zygote contains a pre-warmed execution environment, i.e. required to all app run (e.g., jvm, libraries, etc..). This reduces the start-up time All components run in the same thread.. (but thread can/must be created)

5 Zygote FORK Preloaded classes VM VM VM

6 Interacting via shell ABD is a tool used to interact with the Android OS It gives a limited shell where (some) classical Linux command can be issued, e.g., uname, ps, df, ls,.. ADB can be attached to emulator or real device See some real example, just to have a flavor A full system access is obtained installing termux app

7 Process list

8 Process management Out of memory (OOM) a state where no additional memory can be allocated for use by programs or the operating system. OOM killer is the mechanism the kernel uses to recover memory by killing processes In Android, OOM killer is different from tradition linux because Processes are ranked according to the state of the contained application After killed, an application can be resuemed (the OS allows to persist the app state across kill/resume)

9 Process management Foreground(active) Less likely to be killed Visible process Service Process Hidden Process Empty processes

10 Another example Check the anchestor

11 Sandboxing Each process that runs an anapplication belongs to a unique and different user Files created by an app then cannot be read from other apps Inter-Process (app-to-app) communication via Intent

12 Inter-process communication App-to-app communication occurs using a kind of a message called INTENT An intent can either for an explicit target application (or app component, see later) or the sender wants to perform an action, but it has no idea about whch application can do it (implicit intent) why? can be useful.. for what? Example (just to play ), run them from adb shell. am start -a android.intent.action.view am start -a android.intent.action.view content://contacts/people/

13 Other actions, can you guess? android.intent.action.dial android.intent.action.main android.intent.action.sendto -d sms:123

14 File systems (typical)

15 /System /bin, /xbin/ à Linux binary /frameworks à.jar

16 /System/app

17 Example: access to sqlite3

18 CPU management To reduce battery drain CPU frequency is reduced (1GHz à 50 MHz) Standby Deep sleep (set a timer to weak up) Wakelocks (avoid the CPU go to sleep)

19 CPU usage Make and example on the emulator or a real device

20 Security management (basic stuff) Secure boot chain Only signed OS from known origin can be loaded Integrity, Authenticity OS Update Downgrade not possible Application isolation (user per app) Sandbox Permission-based access control Users grant/revoke permissions to make sensible operations Application signing Only signed apps can be installed (e.g., from Apple) Updates must come from the same developer

21 Higher level resource management Package Manager The system by which applications are able to find out information about other applications currently installed on the device. Telephony Manager Provides information to the application about the telephony services available on the device such as status and subscriber information. Location Manager Provides access to the location services allowing an application to receive updates about location changes. Activity Manager Controls all aspects of the application lifecycle and activity stack. Resource Manager Provides access to non-code embedded resources such as strings, color settings and user interface layouts. Notifications Manager Allows applications to display alerts and notifications to the user.

22 Running an app the traditional way Stack,heap Sw libraries, etc User Process Signal Code to run Run-time support Sys call OPERATING SYSTEM Service System Process (Deamon) The OS manages processes providing the execution environment Call fork and then exec App can system call the OS OS can send sw interrupts Can be ignored, but SIGSEGV,.. Handler can be registered

23 Running app in android Server Process App Process App Process Activty manager All managers in one process Zygote Daemons OPERATING SYSTEM Server process contains all the android managers All processes are forked from ZYGOTE (slow start up time)

24 Android versions NEW

25 Android fragmentation OS update brings new features.. Not all manufactures update the OS Applications then remain old.. How to solve this problem? Support libraries and GPS

26 Support libraries As new features are added (e.g., toolbar, actionbar, fragments, ) support libraries are developed, so that such features are also available to older android versions v4 support, v7 appcompat,etc.. (see documentation) Android API are very dynamic, so it can happen that some method or widget are deprecated (always take a look at the official documentation)

27 Android architecture

28 Android architecture (kernel) Provides a level of abstraction between the device hardware and it contains all the essential hardware drivers like camera, keypad, display etc. Implement network stack, multitasking, etc.. Binder is a special driver designed to provide secure communication between apps

29 Android architecture: ART Introduced with android 5 (before DVM) Register based architecture Code runs directly on hw (as opposed to DVM) Each app runs in its own process and with its own instance of the Android Runtime (ART).

30 Native SW libraries (C/C++) Surface Manager: Rendering of Views 2D graphics Web engine Open GL ES 2D and 3D graphics (Bionic)C standard library Media Framework: Manage different codec, e.g. mp3,h.264,mpeg4,etc.

31 Android framework The entire feature-set of the Android OS is available through Java packages. android.app Provides access to the application model and is the cornerstone of all Android applications. android.content Facilitates content access, publishing and messaging between applications and application components. android.database Used to access data published by content providers and includes SQLite database management classes. android.graphics A low-level 2D graphics drawing API including colors, points, filters, rectangles and canvases. android.hardware Presents an API providing access to hardware such as the accelerometer and light sensor.

32 Bird s eye view to application s components User Interface Views/Layouts Activity Fragment UI runs in a thread à responsiveness Material design Computation Service/Activity Broadcast receiver May use separate thread Implements the business logic Data Preference File SQLite Content provider Cloud Many ways to store data