Mobile Handset Virtual Machine. Outline Virtual Machine Java Virtual Machine Dalvik Virtual Machine...
-
Upload
triston-kilton -
Category
Documents
-
view
318 -
download
0
Transcript of Mobile Handset Virtual Machine. Outline Virtual Machine Java Virtual Machine Dalvik Virtual Machine...
Mobile Handset Virtual Machine
2
Outline
Virtual Machine Java Virtual Machine Dalvik Virtual Machine
3
Concept
A virtual machine (VM) is a software emulation of a real machine so thatanother operating system can run in the simulated
machinemore than one different operating systems can run
at the same time Fundamental idea: abstract the real hardware
into different execution environments
4
VM Components (1)
Three components of a virtual machineHost: underlying hardware systemVirtual machine manager (VMM): creates and runs
different virtual machinesGuest: the emulated operating system on the host
system
5
VM Components (2)
Non-virtual machine Virtual machine
Host
VMM
Guest
6
System/Process VM
Two major kinds of virtual machines based on their emulation degree of real machinesSystem virtual machine: it provides a complete
system platform to support a complete operating system
Process virtual machine: it runs a single program and supports a single process
7
System VM
It usually emulates a platform to run programs where the real hardware is not available to use (for example, running Mac OS on a windows computer)
Multiple OSes can co-exist on the same physical hardware and are strongly isolated from each other
Popular virtual machine manager products: Xen, VMware Workstation, Sun Virtualbox
8
Process VM
It is created when the process is started and destroyed when the process exits. Its purpose is to provide a platform-independent programming environment so that a program can execute in a same way on any platform
For example, Java bytecode can run on any platform where there is a Java Virtual Machine and the code does not need to be recompiled.
9
Outline
Virtual Machine Java Virtual Machine Dalvik Virtual Machine
10
Java Virtual Machine
Java Virtual machine (JVM) is the virtual machine that can execute Java bytecode. It is the execution part of the Java platform
It helps Java to achieve its goal “write once, run anywhere” by hiding the differences between different operating systems
11
Java Bytecode
Java bytecode is the instruction set for Java virtual machine
Each bytecode consists of two partsOne or two bytes that represent the instructionZero or more bytes for parameters
Java compiler compiles Java code into Java bytecode. The Java programmer does not need to be aware of or understand Java bytecode
12
Example of Java Bytecode
Java Compiler
Java CodeJava Bytecode
instruction Fucntion
iconst_n Push the integer constant n onto the stack
istore_n Store an integer value into the variable of index n
iload_n Load an integer value from variable of index n
sipush Push a short integer onto the stack
iinc n i Increase variable of index n by i
13
JVM Workflow (1)
Java source code is compiled into Java bytecode which is stored within .class files
Each class in Java source code will be compiled into one .class file.
The .class files are read and interpreted by JVM
14
JVM Workflow (2)
A.classA.java Java Compiler
B.class
Class Loader
Bytecode Interpreter
Java Virtual Machine
Compile source code
Java API
Host system (Windows, Linux, etc)
15
JVM Components (1)
Class loader Loads .class file into memoryVerifies bytecode instructionsAllocates memory for the program
16
JVM Components (2)
Runtime data area Method area: it stores class and method codes Heap: it is the place where Java objects are created Java stacks: they are places where Java methods are
executed Program counter (PC) registers: they store memory
addresses of the instructions which to be executed Native method stacks: they are places where native
methods (e.g. C programs) are executed. Native method is a function which is written in another language other than Java
17
JVM Components (3)
Native method interface: it is a program that connects native method libraries with JVM for executing native methods
Native method library Execution engine: it contains the interpreter
which converts Java bytecode into machine code
19
Java Runtime Environment
We usually install the Java Runtime Environment (JRE) on our computers to use the Java platform
JRE consists of the JVM and Java APIs
20
Outline
Virtual Machine Java Virtual Machine Dalvik Virtual Machine
21
Introduction
Dalvik virtual machine (DVM) is the process virtual machine in Google’s Android operating system. It executes applications written for Android.
It is open-source software which was originally written by Dan Bornstein, who named it after the fishing village of Dalvik in Iceland
22
Why DVM not JVM
When Google selected Java as the language for developing Android applications, it chose DVM instead of JVM for several reasons:Though JVM is free, it was under GPL license,
which is not good for Android as most the Android is under Apache license
JVM was designed for desktops and it is too heavy for embedded devices
DVM takes less memory, runs and loads faster compared to JVM
23
Android Architecture
Virtual Machine
C/C++
24
Dalvik Bytecode
Dalvik bytecode is the instruction set for Dalvik virtual machine
Android programs are firstly compiled into Java bytecode which is in .class files. A tool called dx then converts Java bytecode into Dalvik bytecode
25
Dalvik Bytecode VS Java Bytecode
Java source code
Dalvik bytecodeJava bytecode
26
Dalvik Bytecode VS Java Bytecode
27
DEX File
A .dex (Dalvik EXecutable) file is used to store the Dalvik bytecode. It is converted from .class files and executed on the DVM
The .dex file has been optimized for memory usage and the design principle is sharing of data
It uses shared, type-specific constant pools as its primary mechanism for saving memory
28
Constant Pool Concept
A constant pool is a table stores all constant values (e.g. string constants, field constants, class constants, etc.) used within a Java class.
Constant values are referred to by their index in the constant pool rather than stored throughout the class
Constant pool is the biggest part of the Java class file and takes up 61% of the file size
29
Constant Pool Optimization (1)
Although average size of one .class file is quite small, the size still matters because the time to read file from storage is a dominant factor in VM startup time
.dex file optimizes the constant pool when converted from .class files
30
Constant Pool Optimization (2)
In the .class file, each class has its own private, heterogeneous constant pool. It is heterogeneous because all types of constants (field, string, class, etc.) are mixed together
In the .dex file, all classes share the same type-specific constant pools. Duplication of constant values across different classes is eliminated
31
Constant Pool Optimization (3)
Java Source Code
(.java files)
Heterogeneous Constant Pool
Other Data
.class
Heterogeneous Constant Pool
Other Data
.class
Heterogeneous Constant Pool
Other Data
.class
Strings Constant Pool
Other Data
.dex
Class Constant Pool
Field Constant Pool
Method Constant Pool
Java Compiler
dx tool
32
Memory Saving Evaluation
The Android team found that .dex file format cuts the size in half of some common system libraries and applications within Android systemCode Size of .class Files
(bytes)Size of .dex File (bytes)
Common System Libraries 21,445,320 (100%) 10,311,972 (48%)
Web Browser App 470,312 (100%) 209,248 (44%)
Alarm Clock App 119,200 (100%) 53,020 (44%)
33
Zygote (1)
Zygote is another concept used by Android to speedup VM performance
Every Android application runs in its own instance of the VM, so VM instances should be able to start quickly when a new application is launched
Zygote enables code sharing across different VM instances and provide fast startup time for new VM instances
34
Zygote (2)
Zygote is a VM process which starts at system boot time. When Zygote starts, it initializes a VM instance and preloads core library classes which are good candidates for sharing across processes
Zygote will sit and wait for socket requests from other processes who need new VM instances
Cold starting VM takes a long time. Once a request occurs, Zygote will fork a new VM instance from itself and the startup time will be minimized
36
Android Runtime
Android Runtime (ART) is an application runtime environment used by Android operating system
It is designed to replace Dalvik virtual machine. It supports standard .dex file to maintain backward compatibility
ART came out as an alternative runtime environment in Android 4.4
Dalvik virtual machine was entirely replace by ART in Android 5.0
37
Java Source Code to Android App
Java Source Code
(.java files)
Dalvik Bytecode.dex file
Java Compiler
dx tool
.class file.class file
.class file.class file
.class file
Java Bytecode
Resource files
Android App.apk file
Package Builder
38
Android Application Launch Procedure Many things happen in the background when a user
clicks on an icon and launch a new application The click event gets routed to activity manager. The activity manager sends parameters to Zygote process
over the socket connection and creates a new process Zygote forks itself and returns the new process ID The activity manager attaches the new process to the
application and the application’s classes will be loaded into the process’s memory
The application is launched
39
References (1) http://en.wikipedia.org/wiki/Virtual_machine http://www.virtual-managed-servers.com/process-virtual-machine.html http://www.virtual-managed-servers.com/system-virtual-machine.html http://courses.mpi-sws.org/os-ss11/lectures/proc9.pdf http://en.wikipedia.org/wiki/Java_virtual_machine http://www.utdallas.edu/~
muratk/courses/cloud11f_files/smith-vm-overview.pdf www.cse.sc.edu/~rose/311/ppt/ch16.ppt http://web.cs.wpi.edu/~cs502/s06/LectureNotes/ http://www.javaservletsjspweb.in/2012/02/java-virtual-machine-jvm-archit
ecture.html#.VOupzfnF9t8
http://skillgun.com/question/436/android/basics/what-is-the-difference-between-dvm-and-jvm-why-android-opted-for-dvm
40
References (2) http://
multi-core-dump.blogspot.com/2010/04/android-application-launch-part-2.html
http://multi-core-dump.blogspot.com/2010/04/android-application-launch.html
http://en.wikipedia.org/wiki/Dalvik_(software) http://www.cs.duke.edu/~chase/cps210/slides/android-chase.pptx