Alma Mater Studiorum University of Bologna CdS Laurea Magistrale (MSc) in Computer Science Engineering

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1 Mobile Systems M Alma Mater Studiorum University of Bologna CdS Laurea Magistrale (MSc) in Computer Science Engineering Mobile Systems M course (8 ECTS) II Term Academic Year 2016/ Development and Runtime Platforms: Overview, J2ME, ios, and Android Paolo Bellavista paolo.bellavista@unibo.it Development/Runtime Platforms Mobile Systems M 1 Overview on Development/Runtime Platforms Many solutions have been proposed in the literature for development/runtime support of mobile systems middleware and applications. Why? Heterogeneity and fragmentation Market-driven choice Very heterogeneous and differentiated characteristics of available devices, platforms, and app requirements Plethora of solutions: Symbian, Palm, RIM, Maemo/Meego, ios, Android, Java Mobile Edition (J2ME),.NET Compact Framework (CF), Python, Lazarus, Brew, Flash Lite, Web runtime environment (microbrowser, HTML5, XHTML/CSS, JavaScript, Mobile Ajax, ), Let s try to put in order Which involved layers? Development/Runtime Platforms Mobile Systems M 2 1

2 Overview on Development/Runtime Platforms Operating system layer (e.g., is Android an operating system?) Runtime execution support layer (frameworks, containers, virtual machines, ) Development support layer - SDK (libraries, support components, containers, ) Again, layers with NO clear borders and NOT easily disjoint Mainly at OS layer: Symbian, Palm, RIM (BlackBerry), Maemo/Meego, ios, Linux?, Mainly at runtime execution support layer: Kernel-based Virtual Machine (KVM) or Dalvik Virtual Machine for Java, Common Language Runtime (CLR) for.net, Flash Lite, Web runtime environment Development/Runtime Platforms Mobile Systems M 3 Overview on Development/Runtime Platforms Mainly at development support layer: J2ME world,.net CF world, ActionScript for Flash Lite, Android world, Web runtime environment Two primary approach categories: Based on native applications Based on Web integration (in particular, see standardization efforts associated with HTML5) Let s start with the first approach, by choosing to have a rapid overview on 4 main families of solutions: J2ME,.NET CF, Flash Lite, and Android Development/Runtime Platforms Mobile Systems M 4 2

3 Overview on J2ME,.NET CF, Flash Lite, and Android Development/Runtime Platforms Mobile Systems M 5 J2ME in a Single Slide Java edition for resource-limited devices (smart phones, settop boxes) embedded/javame/index.html Bytecode is run over Kernel-based Virtual Machines (KVM), full OS independency Configuration concept: minimum feature set for VM + support libraries for a horizontal family of devices Connected Limited Device Configuration (CLDC) Profile concept: specialized libraries for the characteristics of a given type/class of devices Mobile Information Device Profile (MIDP), on top of CLDC Java apps over CLDC/MIDP are called MIDlet Do you already know what Java Community Process (JCP) and Java Specification Request (JSR) are? Development/Runtime Platforms Mobile Systems M 6 3

4 .NET CF in a Single Slide Subset of.net platform (around 30% of classes and features) for MS Windows Mobile devices Exploitation of Common Language Runtime (CLR); in principle, support for different OSs and different programming languages (actually only WinMobile, C#, and VB.NET) Idea of smooth transition from desktop app development to mobile app development, anyway pushed by a big vendor with a large community of developers Cost associated with intermediate code execution (Common Intermediate Language CIL) Relatively high cost in terms of memory footprint It has NO fragmentation problems, differently from J2ME Development/Runtime Platforms Mobile Systems M 7 Adobe Flash Lite in a Single Slide Proprietary technology that was popular for the development of multimedia contents and games Basically, support for vectorial graphics and animations; add-ons of application and presentation logics via ad-hoc programming language, i.e., ActionScript, which runs over a dedicated runtime support Smooth transition for expert Flash developers Incomplete solution for stand-alone full-fledged apps; NO ambition of general purpose solution Strng integration with low-level capabilities of devices, therefore with good efficiency Limited performance due to cost of vectorial graphics management See similar approach in the Java world with JavaFX Mobile Development/Runtime Platforms Mobile Systems M 8 4

5 Android in a Single Slide Launched by Google in 2007 as an Apache free-software platform, based on Linux Applications were developed in Java and compiled into Dalvik Executable format (DEX custom bytecode, e.g., more concise than usual.class) Quite large subset of J2SE facilities + rich library of support features (Android SDK) available for the community of developers Touch screen management, local sensors (accelerometers, gyroscopes, GPS, ), 3D graphics, advanced support for locationbased services, Also here possible? fragmentation issues due to different OS versions and to usage of different extensions of the support stack (given the potential openness of the adopted approach ) Development/Runtime Platforms Mobile Systems M 9 A Comparison with a Toy Application (Gavalas et al, IEEE Software, 2011) Development/Runtime Platforms Mobile Systems M 10 5

6 A First Comparison Development/Runtime Platforms Mobile Systems M 11 A First Comparison Development/Runtime Platforms Mobile Systems M 12 6

7 A First Comparison Development/Runtime Platforms Mobile Systems M 13 A First Comparison Development/Runtime Platforms Mobile Systems M 14 7

8 A First Comparison Development/Runtime Platforms Mobile Systems M 15 By delving into finer technical details: Java 2 Micro Edition In general terms, different editions of Java distributions Central role of the KVM + CLDC + MIDP stack Development/Runtime Platforms Mobile Systems M 16 8

9 Actually, more complex and articulated situation Important fragmentation issues JSR 248: Mobile Service Architecture (MSA) MSA, in two versions: full (17/14) or subset (8/9) Development/Runtime Platforms Mobile Systems M 17 J2ME: Configurations and Profiles A configuration defines a minimal platform for a horizontal group of devices Similar requirements on memory and computing power It defines Java language and virtual machine characteristics that have to be available on the targeted group of devices A Configuration is a specification that defines a minimum Java Platform functionality for a family of devices. It defines the minimum number of Java libraries, VM capabilities, Security specification, and a Generic Connection Framework Profile as a set of additional APIs that extend a configuration with capabilities that are useful for a specific group of devices A Profile is a collection of Java APIs that supplement a Configuration to provide capabilities for a specific device group or market type Development/Runtime Platforms Mobile Systems M 18 9

10 J2ME: Defined Configurations Connected Device Configuration (CDC) Typically for devices with higher resources if compared with lowend phone devices (no more valid nowadays) For example, set-top boxes, initially some kinds of PDAs, Connected, Limited Device Configuration (CLDC) For devices with very limited onboard resources Virtual machine for CLDC: Sun s Kilo Virtual Machine (KVM) Small memory footprint (60K) Overall minimum memory = 160K 16/32-bit processors Processor speed = at least in the range 8-32MHz Typical hardware of CLDC configuration For CLDC the only STRONG requirement is available memory size: At least non-volatile 128K for KVM and CLDC libraries At least volatile 32K for KVM runtime Development/Runtime Platforms Mobile Systems M 19 J2ME Profiles Any profile defines requirements for a family of devices associated with a specific vertical market It extends (with a upper overlay layer) a configuration. Always on top of one defined configuration It defines a standardized Java platform for a device family/class in order to achieve interoperability (effort towards the reduction of fragmentation issues) It includes class libraries with finer granularity if compared with the ones in a configuration Available profiles: Mobile Information Device Profile (MIDP) on top of CLDC. It includes additional features for GUIs, multimedia and gaming support, end-to-end security, extended support to network connectivity for mobile phones and entry-level PDAs Development/Runtime Platforms Mobile Systems M 20 10

11 Defined J2ME Profiles (continued ) Foundation Profile on top of CDC. Set of basic Java APIs for resource-limited devices; crucial and central factor is lack of standard GUI support Personal Profile on top of CDC. Together with Foundation Profile, Personal Profile implements the support for development of high-end PDA applications. Personal Profile includes complete set of AWT APIs, support for applets and Xlets Personal Basis Profile on top of CDC. It provides developers with an environment for the support of applications with network connectivity and an elementary degree of grahics support for content presentation Development/Runtime Platforms Mobile Systems M 21 MIDP: Hardware Requirements Memory (in addition to the one requested by CLDC) 128K non-volatile for MIDP components 8K non-volatile for persistent application data 32K volatile for KVM Display Screen with at least 96x54 pixels Display depth (or color depth or bit per pixel) at least equal to 1-bit Form factor of pixels (aspect ratio) = 1:1 Input peripherals (one or multiple) One-handed keypad Two-handed keypad Touch screen Networking Two-way Wireless Management of intermittent connectivity Limited bandwidth Development/Runtime Platforms Mobile Systems M 22 11

12 Original Equipment Manufacturer (OEM) MIDP Architecture MIDP Applications MIDP OEM-Specific Applications OEM-Specific Classes Device-Native Applications CLDC Native OS + System Software Mobile Information Device (MID) Development/Runtime Platforms Mobile Systems M 23 Class Libraries CLDC java.lang java.io java.util javax.microedition.io MIDP javax.microedition.lcdui javax.microedition.midlet javax.microedition.rms Development/Runtime Platforms Mobile Systems M 24 12

13 destroyapp destroyapp pauseapp startapp MIDP Application Model MIDP applications are called MIDlets MIDlet model is, under many perspectives, similar to the applet model in J2SE: component-container model and lifecycle management Also security support for applications that share resources/data (via MIDlet Suite) MIDlet lifecycle is described as state transitions, indicated as: Start resource acquisition and execution start Pause resource release and entrance in the wait state Destroy resource release, thread destruction, and ending of all activities Java Application Manager (JAM) for MIDlet lifecycle management Pause Active Destroyed Development/Runtime Platforms Mobile Systems M 25 Typical J2ME Support Stack KVM + CLDC + MIDP: applications are developed and run on top of this standardized stack, independently from OS and hw details CLDC = KVM + J2ME Core API in this example Mobile Information Device Profile KVM Your MIDlet J2ME core APIs DSP chip (e.g., ARM) Yellow pages, train timetable and ticketing, games, UI, HTTP networking,... Thread support, no floating point 32-bit RISC, 256K ROM, 256K Flash, 64K RAM Development/Runtime Platforms Mobile Systems M 26 13

14 Package CLDC/MIDP: some Detail about the Primary Packages javax.microedition.io javax.microedition.lcdui (user interface for lcd displays) javax.microedition.midlet javax.microedition.rms (persistent storage) Widget support for user GUIs Form, TextField, TextBox, DateField, List, Image, Gauge, Alert, Canvas, Graphics, Display Two different types of APIs (lower and higher abstraction layers) for GUI management High level for widget, scrolling,... Low level for graphics fine-grained GUI control Classes for event management Command and CommandListener Most relevant: is obvious for all, isn t it?, which is the underlying threading model? Development/Runtime Platforms Mobile Systems M 27 import javax.microedition.lcdui.*; import javax.microedition.midlet.*; public class HiMIDlet extends MIDlet { Usual Hello World as a MIDlet private TextBox textbox; public HiMIDlet() { textbox = new TextBox ("", "Hello World!", 20, 0); } public void startapp() { Display.getDisplay(this).setCurrent(textbox); } public void pauseapp() {} public void destroyapp(boolean unconditional) {} } Development/Runtime Platforms Mobile Systems M 28 14

15 import javax.microedition.midlet.*; import javax.microedition.lcdui.*; MIDlet: Simple GUI Management public class HelloWorld extends MIDlet implements CommandListener { private Form mainscreen; private Form detailsscreen; private Display mydisplay; private Command exitcommand; private Command resetcommand; private Command detailscommand; public HelloWorld(){ } mydisplay = Display.getDisplay(this); mainscreen = new Form("Hello World"); detailscommand = new Command("Details",Command.SCREEN, 1); resetcommand = new Command("Reset",Command.SCREEN,1); exitcommand = new Command("Exit", Command.EXIT, 1); Development/Runtime Platforms Mobile Systems M 29 MIDlet: Simple GUI Management StringItem stritem = new StringItem("Hello", " World"); mainscreen.addcommand(detailscommand); mainscreen.addcommand(resetcommand); mainscreen.addcommand(exitcommand); mainscreen.append(stritem); mainscreen.setcommandlistener(this); public void startapp() { mydisplay.setcurrent(mainscreen); } protected void pauseapp() { } protected void destroyapp(boolean unconditional) { } Development/Runtime Platforms Mobile Systems M 30 15

16 MIDlet: Simple GUI Management public void commandaction(command c, Displayable s) { if (c == exitcommand) { destroyapp(false); notifydestroyed(); } else if (c == detailscommand) { detailsscreen = new Form("Details"); detailsscreen.addcommand(resetcommand); detailsscreen.setcommandlistener(this); mydisplay.setcurrent(detailsscreen); } else if (c == resetcommand) { mydisplay.setcurrent(mainscreen); } } } Development/Runtime Platforms Mobile Systems M 31 import java.io.*; import javax.microedition.io.*; import javax.microedition.midlet.*; import javax.microedition.lcdui.*; MIDlet: a more Realistic Example public class PrimitiveMIDlet extends MIDlet implements CommandListener { private Display mdisplay; private Form mmainform; private Command mexitcommand, mconnectcommand; public void startapp() { mdisplay = Display.getDisplay(this); if (mmainform == null) { mmainform = new Form("PrimitiveMIDlet"); mmainform.append(new StringItem("", "Select Connect to make a network connection")); mexitcommand = new Command("Exit", Command.EXIT, 0); mconnectcommand = new Command("Connect", Command.SCREEN, 0); Development/Runtime Platforms Mobile Systems M 32 16

17 mmainform.addcommand(mexitcommand); mmainform.addcommand(mconnectcommand); mmainform.setcommandlistener(this); } mdisplay.setcurrent(mmainform); } MIDlet: a more Realistic Example public void commandaction(command c, Displayable s) { if (c == mexitcommand) notifydestroyed(); else if (c == mconnectcommand) connect(); } private void connect() { String url = getappproperty("networkthreading.url"); try { //interroga server e riceve risposta HttpConnection hc = (HttpConnection)Connector.open(url); InputStream in = hc.openinputstream(); int contentlength = (int)hc.getlength(); if (contentlength == -1) contentlength = 255; byte[] raw = new byte[contentlength]; int length = in.read(raw); Development/Runtime Platforms Mobile Systems M 33 } MIDlet: a more Realistic Example in.close(); hc.close(); // Show the response to the user. String s = new String(raw, 0, length); Alert a = new Alert("Response", s, null, null); a.settimeout(alert.forever); mdisplay.setcurrent(a, mmainform); } catch (IOException ioe) { Alert a = new Alert( "Exception", ioe.tostring(), null, null); a.settimeout(alert.forever); mdisplay.setcurrent(a, mmainform); } } public void pauseapp() {} public void destroyapp(boolean unconditional) {} Which possible issues in a real usage scenario? Development/Runtime Platforms Mobile Systems M 34 17

18 MIDlet: a more Realistic Example Which possible issues in a real usage scenario? NO GUI feedback during the time interval needed for connection establishment => «no-waiting» user that generates other useless commands Most relevant: threading model System threads are offered for MIDlet execution The only threads fully and exclusively owned by a MIDlet are the ones that MIDlet explicitly instantiates As in other technologies, e.g., for GUI management: a system thread works as event dispatcher; event managers have to rapidly return control in order not to block the MIDlet interface Therefore, the «right and sound» solution would be Development/Runtime Platforms Mobile Systems M 35 MIDlet: a more Realistic Example } public void commandaction(command c, Displayable s) { if (c == mexitcommand) notifydestroyed(); else if (c == mconnectcommand) { Thread t = new Thread() { public void run() { connect(); } }; t.start(); } Which possible issues in this case? Development/Runtime Platforms Mobile Systems M 36 18

19 SingleWorker class public synchronized void run() { while (mtrucking) { try { wait(); } catch (InterruptedException ie) {} if (mtrucking) connect(); } } public synchronized void go() { notify(); } MIDlet: a more Realistic Example SingleMIDlet class import java.io.*; public class SingleMIDlet extends MIDlet implements CommandListener { private Display mdisplay; private Form mmainform, mwaitform; private SingleWorker mworker; private Command mexitcommand, mconnectcommand, mcancelcommand; Development/Runtime Platforms Mobile Systems M 37 public void startapp() { mdisplay = Display.getDisplay(this); if (mmainform == null) { //preparazione form mworker = new SingleWorker(this, url); mworker.start(); } mdisplay.setcurrent(mmainform); } public void commandaction(command c, Displayable s) { if (c == mexitcommand) notifydestroyed(); else if (c == mconnectcommand) { mdisplay.setcurrent(mwaitform); mworker.go(); } else if (c == mcancelcommand) { mdisplay.setcurrent(mmainform); mworker.cancel(); } } public void pauseapp() {} public void destroyapp(boolean unconditional) { mworker.stop(); } MIDlet: a more Realistic Example Development/Runtime Platforms Mobile Systems M 38 19

20 J2ME: Types of Supported Web Connections HTTP/HTTPS Simple to use XML over HTTP/HTTPS Recently most widespread usage thanks to availability of several lightweight parsers Model: it creates object-based representation of a doc n memory, e.g., DOM Push: it parses a whole document, by distributing then events to the registered listeners, e.g., SAX Pull: it parses the document a part after the other (fragment), by returning a single element or tag In addition, very often, exploitation of features defined in additional JSRs: among the others, JSR82 (Bluetooth), JSR179 (Location), JSR135 (Mobile Media), JSR180 (SIP), and JSR172 (Web Services) Development/Runtime Platforms Mobile Systems M 39 Identifying the target devices Exercise on J2ME: How to Design a MIDlet Application Identifying the profiles that are supported by those devices Developing the application For instance, if as a MIDlet because CLDC/MIDP is supported, application suitable for cellphones and small pagers The development environment should be integrated with CLDC/MIDP: MIDP reference implementation Possibility of execution (for validation and testing purposes) over MIDP emulators For example, usage of J2ME Wireless Toolkit and ktoolbar to create a project and to design, implement, configure, and validate a MIDlet Probably you will appreciate more working with Eclipse ME Development/Runtime Platforms Mobile Systems M 40 20

21 For example, Nokia J2ME SDK Development/Runtime Platforms Mobile Systems M 41 Remember: MIDlet Upload Process Advertise App on Web Page User Selects App JAM Downloads App Web Page (Name, Version, Size, ) Descriptor File Network Transfer Java Application Manager Jar File Development/Runtime Platforms Mobile Systems M 42 21

22 Optional Exercise on J2ME: How to Design a MIDlet Application To design and develop a simple context-dependent MIDlet (e.g., able to play sounds or multimedia files that are differentiated depending on current user location), by exploiting features of JSR 135 (known as Mobile Media API, and of JSR 179 (known as Location API, different implementation more or less easily available, e.g., Exploiting, as preferred, development tools and IDEs such as JavaME Wireless Toolkit or Eclipse ME Note that the support for old-fashioned technologies such as Java ME is decreasing and decreasing Development/Runtime Platforms Mobile Systems M 43 A Superficial Overview of the Security Model JME CANNOT support the regular and complete security model of J2SE The implementation of the only J2SE protection domains is larger than the whole CLDC implementation (footprint) Therefore, how to implement a security solution for JME? Main guideline to split the problem into two parts: VM-level security (low-level) Obtained via the 2-phase verifier for class files that is included in CLDC Application-level security Sandbox model Development/Runtime Platforms Mobile Systems M 44 22

23 Security: Class File Verifier in 2 Phases Off-device verification Tool for pre-verification adds a stack map attribute to any method in the Java class file in order to facilitate in-device verification Pre-verification process (computationally heavyweight) is run on server/desktop side before that the class file is downloaded on mobile device stack map then helps to make more efficient the in-device verification Faster Less code in VM and minor memory consumption In-device verification Environment verification (e.g., memory requirements at runtime) Bytecode check Type check Proper termination, i.e., adequate and robust (e.g., no instructions for unconditional jump) Development/Runtime Platforms Mobile Systems M 45 Security: Class File Verifier in 2 Phases Stack map attribute grows the size of classfile of around 5% Development/Runtime Platforms Mobile Systems M 46 23

24 Application-level Security: Sandbox Model Applications (MIDlets, but not only them) have to execute in a close environment from where they can access only the APIs defined by configuration, profile, and licensed classes that are supported by the used device Do you remember the sandbox execution model for applets? More specifically, MIDlet sandbox model specifies: Class files have to pass an adequate verification step (to guarantee they are valid) Only the APIs defined by CLDC, profile, and licensed extension classes have to be available Application download occurs at so-called native layer (native code level), mandatorily via the Java Application Manager (JAM) Forbidden to override the standard class loading mechanism Forbidden the access to the set of native functions that the VM can instead use Development/Runtime Platforms Mobile Systems M 47 Android: Architecture Classical hierarchical architecture, structured into layers (growing complexity from bottom to top) Layers: Linux kernel Libraries (native Linux) + Android runtime (Dalvik VM + core libraries) Application Framework Applications Development/Runtime Platforms Mobile Systems M 48 24

25 Android: Architecture Kernel Layer Based on traditional Linux v3.x kernel and evolutions It introduces Hardware Abstraction Layer (HAL) Libraries in native language (C/C++) Android Runtime Execution environment for applications, written in Java Based on Dalvik VM Application Framework It provides applications with advanced services, encapsulated in Java objects, Application Core Apps: provided by the «initial» onboard system Developers written apps Development/Runtime Platforms Mobile Systems M 49 Android: Elements about Version Evolution Ice Cream Sandwich (October 2011) Linux kernel 3.0.1; customizable launcher; "Contacts" app fully integrated with main social network applications; Android Beam (data exchange via NFC); Wi-Fi Direct, etc. etc. Development/Runtime Platforms Mobile Systems M 25

26 Android: Elements about Version Evolution Jelly Bean (July 2012) Linux kernel ; new features for picture/video sharing via NFC; advanced voice recognition; official end of the support of Adobe Flash, etc. etc. Kit Kat 4.4 (October 2013) Support for 3 new types of sensors (geomagnetic rotation vector, step detector and counter), added step counter feature; decreased battery consumption during audio playing; Android RunTime (ART) and new compiler, experimental in this version, that can be activated in Developers Options (not on all devices); optimized working on devices with limited RAM, Development/Runtime Platforms Mobile Systems M Android: Elements about Version Evolution Lollipop (November 2014) Introduction of Google Fit for physical activity; new Linux 3.10.x. kernel; removal of Dalvik runtime, that is officially replaced by ART; native 64 bit support; Bluetooth 4.1; improvement of graphical performance thanks to OpenGL ES 3.1 support; improvement of camera support thanks to dedicated APIs; added multi-user features on smartphones; Marshmallow 6.0 (October 2015) Doze mode, with CPU speed reduction when display is switched off; native support to fingerprint readers; Direct Share for sharing among apps; request of post-install/run-time permissions; USB Type-C support; support to External storage to make it uniform to Internal Storage; MIDI support for music instruments; experimental multi-window feature Development/Runtime Platforms Mobile Systems M 26

27 Android: Elements about Version Evolution Nougat «N» (August 2016) Ability to display multiple apps on-screen at once in a split-screen view; support for inline replies to notifications; OpenJDK-based Java environment; support for the Vulkan graphics rendering API; "seamless" system updates on supported devices; Development/Runtime Platforms Mobile Systems M Kernel Linux 3.x Hardware Abstraction Layer (HAL) Memory management Process management Network stack Standard Linux power management Android: OS Kernel Layer Kernel extensions Ashmem: shared memory manager; reference counting and automatic deallocation by the kernel IPC binder: low overhead thanks to the usage of Ashmem (rigid access discipline via memory block descriptors) Advanced power management: exploitation of different energy management policies via WakeLocks It is NOT a real complete Linux OS kernel. It lacks: Native window manager system Complete support to GNU C library Complete support to standard Linux utilities 54 Development/Runtime Platforms Mobile Systems M 54 27

28 Power Management and WakeLocks Manifest example of cross-layering Android apps (with permission to access Power Manager) can achieve control of energy consumption by enforcing the desired policy: Always active CPU, also with switched-off display Prioritary CPU with display that is at least backlit Via WakeLocks: access locks to the features of Power Manager (different types of WakeLock). For protected void oncreate(bundle savedinstancestate) { PowerManager pm = (PowerManager) getsystemservice(context.power_service); wl = pm.newwakelock(powermanager.full_wake_lock, "DoNotDimScreen"); protected void onpause() { super.onpause(); wl.release(); } Development/Runtime Platforms Mobile Systems M 55 Native libraries for graphics and multimedia App Android: Native Libraries and Dalvik VM 3D Surface 2D Surface Media Player Service Media Server Media Recorder Service Surface Flinger Camer a Service Frame Buffer Audio Flinger Vorbis MIDI OpenCORE Camera Surface Manager + Media Framework Dalvik VM designed for mobile devices: registry-based (exploiting the ARM architecture). Instead, how is the traditional JVM organized? It interprets and runs dex files, obtained via transformation of class files (30% reduction of necessary instructions and improvement of runtime perf) optimized support to garbage collection Development/Runtime Platforms Mobile Systems M 56 28

29 Android: Application Framework Activity A single action that one user can accomplish via a window (it corresponds usually to a single screen) It is the fundamental Android component E.g., home activity Intent Maximum reusability of activity Request to perform an operation (e.g., choice of a phone number) Received by a component that has a compatibile Intent Filter Service Running in background (no interaction with user, differently from activity) Usable by 1+ components No dedicated process/thread in background Broadcast Receiver Responds to compatible Intents by executing the associated operations Typically, notify actions (calls, sms transmissions, ) Lifecycle is limited to the response Differently from activities and services, multiple receivers can be activated by a single intent Development/Runtime Platforms Mobile Systems M 57 Package and Activity Manager Manage the lifecycle of Activities and apps, included in Android Packages (APK). Each APK includes a descriptor (manifest), executable dex, and the associated «static» resources (xml, png, ), according to a predefined file structure Window Manager and View System Offer advanced graphics features that can be used directly in apps. View System is based on the View class, and consists of GUI components that interact with user and with event managers (no Java Swing, no AWT) Resource Manager and Content Provider Resource manager for any resource (all files except for code) and shared access to local data (SQLite RDBMS and persistence through files) Telephony, Notification, and Location Manager Allow to access functionality for telephony, notification, and positioning Android: Application Framework Applications Development/Runtime Platforms Mobile Systems M 58 29

30 Bundle Core Applications Real and regular apps (same execution model as for apps developed by third parties and downloaded by users), pre-installed at default over an Android device Home application (and associated activity): manager app frm which it is possible to launch execution of other apps. Which threading model? Message management Client app for Contact book Map management Applications Web browser: WebKit browser engine (open-source); used also in Safari and Google Chrome Only browser engine (HTML parser + renderer + JavaScript engine) Android: Core Applications Development/Runtime Platforms Mobile Systems M 59 Activity is the component for user interaction It extends the Activity Java class In general, many activities are running concurrently: the active one (RUNNING) is only ONE. If visible but not active, it is PAUSED, otherwise STOPPED For lifecycle management, it is possible to redefine callback methods OnCreate, OnStart, OnResume, Activities use resources: an activity may be deallocated due to resource shortage KILLED state Android offers an info container called Bundle, where to save the state to be recovered at re-allocation Lifecycle Management of Android Activities Activity comes back in foreground INACTIVE (KILLED) Resource shortage OnCreate() OnStart() OnRestoreInstanceState(Bundle) OnResume() RUNNING a) New activity b) Back button OnSaveInstanceState(Bundle) OnPause() PAUSED Activity is no more visible OnStop() STOPPED OnDestroy() INACTIVE Activity comes back in foreground OnRestart() Activity comes back in foreground Development/Runtime Platforms Mobile Systems M 60 30

31 MyActivity it.mypackage process Contacts Dialer Dialer process App Dialer MyFirstProject TASK Contacts MyActivity top of the stack root activity Conversation Concept: Android Task One App may include several activities: Independent and disjoint Associated the one with the other Activities are different from forms They should be simple They should be usable and reusable there is the need to structure activities to compose a more complex conversation with user (as for Web pages) A task models a conversation It includes an activity stack, also of different apps: on top the only active activity in the task Activity start pushes it on top of the stack; its closing discards the activity from the stack It may be in foreground or in background Development/Runtime Platforms Mobile Systems M 61 Intent and Intent Filter Activation of a component is triggered by an Intent (usually to pass from an activity to the following one) explicit: component to activate is known at compile time; it needs the Class descriptor of the component implicit: component to activate is NOT known at compile time; it needs that the following data are specified action and category: they describe respectively action and type of the component to activate for execution url: it specifies data to be processed by the activated component mime type: it specifies the data type used Intent intent = new Intent(Intent.ACTION_VIEW); intent.setdata(uri.parse( )); Component is selected based on applicable Intent Filters (description of which intents an activity can handle) that are declared in the manifest, according to an algorithm of Intent Resolution Intent repository on Development/Runtime Platforms Mobile Systems M 62 31

32 Intent and Intent Filter <activity android:name="intentactivity"> <intent-filter> <action android:name="android.intent.action.main" /> <category android:name="android.intent.category. LAUNCHER" /> <category android:name="it.mypackage.intent. category.cat_name" /> <data android:mimetype="vnd.android.cursor.item/ vnd.mytype" /> </intent-filter> </activity> Example of manifest file protected void oncreate(bundle savedinstancestate) {... Intent intent = new Intent(); intent.setaction(my_action); intent.addcategory(intent.category_alternative); intent.addcategory(intent.category_browsable); Uri uri = Uri.parse("content://it.mypackage/items/"); intent.setdata(uri); intent.settype("vnd.android.cursor.item/vnd.mytype"); startactivity(intent);... } Development/Runtime Platforms Mobile Systems M 63 Threading Model in Android Each application has a single thread (at default) => simple single-threaded model (1 app: 1 thread) 1 app: 1 system thread assigned to the app: multiple activities Possibility to save the state in info bundle (not very different from execution model of stateful session beans in J2EE) Each thread has a Looper for message queue management Development/Runtime Platforms Mobile Systems M 64 32

33 Threading Model in Android Two options: 1) to launch different apps in a single Dalvik VM (single heavy process); 2) to have a single Dalvik VM (process) dedicated to each single app The default is the second option: any app is put in execution into a separated VM (separated isolated process), also when triggered by startactivity(intent) or startservice(intent) How is it possible? Which potential issues? For instance, how to perform response return to the «invoking» activity? startactivityforresult(intent, int) second parameter identifies the call callback function onactivityresult(int, int, Intent) If it is crucial to optimize system resource consumption, there is the need to impose that different apps share the same userid Android.sharedUserId= PaoloBellavista in manifest file Which potential security issues? Development/Runtime Platforms Mobile Systems M 65 Android Scheduling Process level: 1. Foreground 2. Visible 3. Service 4. Background App A App B Foreground Thread Group App A Background Thread Group App B > 90% Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND); < 10% Development/Runtime Platforms Mobile Systems M 66 33

34 Asynchronous Techniques Thread Executor HandlerThread AsyncTask Service (already partially discussed) IntentService AsyncQueryHandler Loader Development/Runtime Platforms Mobile Systems M 67 Android Threads Act much like usual Java Threads Cannot work directly on external User Interface objects (throw the Exception CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views ) Cannot be stopped by executing destroy() nor stop(). Use instead interrupt() or join() (by case) As usual, two main ways of having a Thread that executes application code: Providing a new class that extends Thread and overriding its run() method Providing a new Thread instance with a Runnable object during its creation. In both cases, start() method must be explicitly called to actually execute the new Thread Development/Runtime Platforms Mobile Systems M 68 34

35 Android Handler Associated with a single thread and that thread's message queue Bound to the thread/message queue of the thread that has created it It delivers messages and runnables to that message queue It executes them as they come out of the message queue Two main types of usage for a Handler: To schedule messages and runnables to be executed as some point in the future To add an action into a queue performed on a different thread Development/Runtime Platforms Mobile Systems M 69 Handler Example Development/Runtime Platforms Mobile Systems M 70 35

36 Android AsyncTask Created on the UI thread and can be executed only once Run on a background thread and result is published on the UI thread The three parameters of an AsyncTask are: Params, the type of the parameters sent to the async task upon execution Progress, the type of the progress units published during the background computation Result, the type of the result of the background computation Go through 4 steps: onpreexecute(): invoked on the UI thread immediately after the async task is started doinbackground(param...): invoked on the background thread immediately after onpreexecute() finishes executing onprogressupdate(progress...): invoked on the UI thread after a call to publishprogress(progress...) onpostexecute(result): invoked on the UI thread after background computation finishes Development/Runtime Platforms Mobile Systems M 71 AsyncTask Example Development/Runtime Platforms Mobile Systems M 72 36

37 To Summarize: Pay Attention Violate the single thread model: the Android UI toolkit is not thread-safe and must always be manipulated on the UI thread In this piece of code, ImageView is manipulated on a worker thread, which can cause really weird problems. Tracking down and fixing such bugs can be difficult and time-consuming Development/Runtime Platforms Mobile Systems M 73 To Summarize: Pay Attention Classes and methods also tend to make the code more complicated and more difficult to read It becomes even worse when implementing complex operations that require frequent UI updates Development/Runtime Platforms Mobile Systems M 74 37

38 To Summarize: Pay Attention Development/Runtime Platforms Mobile Systems M 75 Example: Developing a Launcher for Replacing the usual Home As already mentioned, home allows starting any app, serving as a launcher Android as an open platform All Apps are created equal it is possible to customize the system with our own home A custom home can be created by: 1. Defining a new Activity 2. Declaring the launcher s action MAIN in the Intent Filter 3. Searching installed apps via Package Manager 4. Selecting the only apps that have an Intent Filter related to launch 5. Creating a selection View (Button) for each suitable app 6. Defining the click event: Intent notification 7. Association of the event to the View Development/Runtime Platforms Mobile Systems M 76 38

39 Example: Developing a Launcher for Replacing the usual Home // Step 1: definition of a new activity public class CategoryTestActivity extends Activity { public void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.main); LinearLayout activitieslist; activitieslist = (LinearLayout) findviewbyid(r.id.activitieslist); // Steps 3 and 4: app search and selection based on IntentFilter Intent intent = new Intent(); intent.setaction(intent.action_main); intent.addcategory(intent.category_launcher); PackageManager pkgmanager = getpackagemanager(); List<ResolveInfo> activities = pkgmanager.queryintentactivities(intent, 0); Development/Runtime Platforms Mobile Systems M 77 Example: Developing a Launcher for Replacing the usual Home for (ResolveInfo resolveinfo : activities) { final ResolveInfo ri = resolveinfo; Button button = new Button(this); //Step 5: one button per app button.settext(resolveinfo.loadlabel(pkgmanager)); // Step 7: event-view association button.setonclicklistener(new OnClickListener() { public void onclick(view v) { Intent intent = new Intent(); //Step 6: intent launch ComponentName cn = new ComponentName(ri. activityinfo.packagename, ri.activityinfo.name); intent.setcomponent(cn); intent.addflags(intent.flag_activity_new_task); intent.addflags(intent.flag_activity_multiple_task); startactivity(intent);}}); activitieslist.addview(button);}}} Development/Runtime Platforms Mobile Systems M 78 39

40 Example: Developing a Launcher for Replacing the usual Home <manifest xmlns:android=... package="it.mypackage"> <application android:label="@string/app_name"> <activity android:name=".homeactivity" android:label="@string/app_name"> <intent-filter> <! Step 2 --> <action android:name="android.intent.action.main" /> <category android:name="android.intent.category.launcher" /> <category android:name="android.intent.category. HOME"> </category> <category android:name="android.intent.category. DEFAULT"></category> </intent-filter> </activity> </application> </manifest> Development/Runtime Platforms Mobile Systems M 79 Typical guidelines for security in Linux Android Security in a Single Slide At default any Android app runs in a dedicated Dalvik VM and within its own separated process. Which PID/GID? Process and group identifiers are selected from an interval that is defined system-level: FIRST_APPLICATION_UID, LAST_APPLICATION_UID Process-level permissions are assigned and controlled depending on user ID & group ID assigned to processes. Typically what do you expect? Finer grain permissions are assigned (and revocable) even for a single operation via manifest file <manifest xmlns:android=" android package="com.google.android.app.myapp" > <uses-permission id="android.permission.receive_sms" /> </manifest> Development/Runtime Platforms Mobile Systems M 80 40

41 Exercise on Android To design and develop a simple context-dependent Android app (for example, able to play different audio/video files depending on current user location), by employing the APIs of the Media Framework library (native) and the APIs of the Location Manager (Java-based, application framework level) Suggestion to use, but free personal choice : Android Studio and SDK tools It could be the initial starting seed for a possible project activity As additional examples of Android usage and project activities, please see also Development/Runtime Platforms Mobile Systems M 81 Many and Many Available Sources for Additional Info Many good (not only good ) books on Android: E. Hellman, Android Programming: Pushing the Limits, Wiley, Nov Z. Mednieks, L. Dornin, Programming Android: Java Programming for the New Generation of Mobile Devices, O Reilly, Ott R. Meier, Professional Android 4 Application Dev., Wrox, 2012 F. Ableson, R. Sen, Android in Action, Manning, Feb Android SDK has good manuals and how-tos, e.g., description of available APIs, presentation of examples of apps, Further info and documents are available at the Android Studio Web site: Development/Runtime Platforms Mobile Systems M 82 41

42 ios (or iphoneos): a Very Rapid Overview Approach is very similar to Android from many perspectives and in terms of realization of a wide support ecosystem, i.e., development model + support API: ios exploits a variantof the XNU kernel, which is at the basis of MacOSX Chain of development tools is similarly based on Xcode SDK includes APIs at different layers to support: Events and multi-touch controls Accelerometer Localization (i18n) Camera and media in general (audio mixing&recording, video playback, several image file formats, OpenGL ES ) Networking Embedded SQLite database Core Location (GPS, Skyhook WiFi, ) Thread Power management File system Security SDK also includes iphone Simulator, i.e., a tool to emulate iphone look&feel over developer desktop. It is not a real emulator: it runs code that is actually generated for another target (x86) SDK requires a Mac OS X Leopard host (or more recent) Development/Runtime Platforms Mobile Systems M 83 ios (or iphoneos): Rules Rules Rules Applications may only use Documented APIs in the manner prescribed by Apple and must not use or call any private APIs. Applications must be originally written in Objective-C, C, C++, or JavaScript as executed by the ios WebKit engine, and only code written in C, C++, and Objective-C may compile and directly link against the Documented APIs An Application may not itself install or launch other executable code by any means, including without limitation through the use of a plug-in architecture, calling other frameworks, other APIs or otherwise. No interpreted code may be downloaded or used in an Application except for code that is interpreted and run by Apple s Documented APIs and built-in interpreter(s) Even the SDK can be downloaded for free but calls for registration to iphone Developer Program if developers are willing to release some software (paying a fee + subject to Apple s approval) Apple has not announced any plan for supporting Java over iphones; initially some partial support instead for J2ME over ios Development/Runtime Platforms Mobile Systems M 84 42

43 Multitasking ios Multitasking Earlier than iosv4, multitasking was limited to a subset of apps defined by producers. Apple was worried about excessive battery consumption due to the concurrent execution of third-party apps Starting from iosv4, multitasking is supported through 7 APIs for background execution: Audio in background - Voice over IP Location service in background - Push notifications Local notifications - Task termination Fast switching of apps Is ios an open system? ios Android Open Source NO YES Write anything you want NO YES Device Homogeneity YES NO Development/Runtime Platforms Mobile Systems M 85 To start: Download the ios SDK, which includes: Xcode iphone emulation tools Monitoring tools Interface builder How to Develop in ios: First Steps Please note that apps are subject to Apple s approval (included in the signed agreement for SDK download), with the idea of performing reliability tests and other investigations Apps may be rejected if evaluated as of "limited utility" Development/Runtime Platforms Mobile Systems M 86 43

44 Alternative Possibilities for ios Development Primary option: exploitation of Xcode and Objective C, exactly same way as in traditional MacOSX Alternatively: Web applications that employ AJAX/Javascript technologies; possibility to access via Safari Usage of Java J2ME and AlcheMo for iphone Xmlvm Java installation over unlocked and jailbroken iphone By the way, do you know what the terms unlocking and jailbreaking mean? Development/Runtime Platforms Mobile Systems M 87 Unlocking & Jailbreaking To be precise, unlocking and jailbreaking identify two different procedures Unlocking is the process through which a device is made compatible with telco networks for which it was not specifically licensed (overcoming the locking with a given dedicated telco operator) Jailbreaking is the process through which a developer exits her own jail in UNIX-like OS and/or breaks the imposed system of Digital Right Management (DRM). It is a specific form of growth of execution privilege In ios, it allows a user to execute arbitrary code and apps, by bypassing the regular mechanism of distribution of Apple code (based on itunes App Store and itunes Application) To enjoy yourself with experimentation, tools such as: PwnageTool, QuickPwn, Yellowsn0w Pusher - Linux on iphone - ZIPhone - Development/Runtime Platforms Mobile Systems M 88 44

45 ios: AJAX & JavaScript AJAX ( maybe Asynchronous JavaScript and XML): set of correlated techniques for the development of highly interactive Web applications (rich Internet applications) Possibility of asynchronous data retrieval in background, with no interference on behavior and visualization of current page To some extent and from some perspectives, applets as AJAX precursors With Safari browser, possibility of highly interactive and native looking Web applications Question: which pros in using Web applications in place of native apps? AJAX plugin per Eclipse (available also as a standalone version): Development/Runtime Platforms Mobile Systems M 89 Also proposals that succeeed in terms of standardization. For example: Canvas element as third-party JavaScript extension that allows dynamic rendering of bitmap images Introduced by Apple for usage within Webkit component of MacOSX (forming the basis of Safari browser), then adopted by Mozilla and Firefox Standardized by WHATWG (see last slide) for the new specification proposals towards HTML5 Canvas is a drawable area defined in the HTML code, with attributes for height and size. JavaScript code can use a wide set of drawing functions, by allowing to use dynamically generated graphics (drawings, animations, image compositions/elaborations, ) In competition with Macromedia Flash/FlashLite. For instance, see these two examples: ios: AJAX & JavaScript Development/Runtime Platforms Mobile Systems M 90 45