Menu
The Android Java is to be executed by the Dalvik virtual machine (VM), which is quite different from the traditional Java VM such as Oracle's HotSpot VM. That is, Dalvik employs register-based bytecode while HotSpot employs stack-based bytecode, requiring a different way of interpretation. Download Free Trial. Undx is a bytecode translator, it converts the bytecode for the dalvik vm (a virtual machine for android applications).
Dalvik is the name of the Virtual Machine in which Android applications are run. This VM executes Dalvik bytecode, which is compiled from programs written in the Java language. Note that the Dalvik VM is not a Java VM (JVM).
Every Android application runs in its own process, with its own instance of the Dalvik virtual machine.
At boot time, a single virtual machine, called 'zygote' is created, which preloads a long list of classes. (As of Android version 2.1 (eclair), the list of classes preloaded by zygote had 1,942 entries). All other 'java' programs or services are forked from this process, and run as their own process (and threads) in their own address space. Both applications and system services in the Android framework are implemented in 'java'.
Dalvik was written so that a device can run multiple VMs efficiently. The Dalvik VM executes code in the Dalvik Executable (.dex) format which is optimized for minimal memory footprint. The VM is register-based, and runs classes compiled by a Java language compiler that have been transformed into the .dex format by the included 'dx' tool.
Most Android applications are delivered and stored on the system as packages (.apks), which include both dex bytes code (classes and methods) and resources. During first boot-up the system creates a cache of dex classes in /data/dalvik-cache.
- 6Debugging the VM
Documentation
There is some documentation on Dalvik in the source code in the dalvik/docs directory.See the Android dalvik docs git repository.
The source code has some rather large comments, including near the top of Thread.c and Exception.c. The 'mterp' directory has some notes describing the structure of theinterpreters.
Q&A
From fadden on the android-platform list:
- Who is responsible to read the dex file and call Dalvik ?
- The VM is started by the framework, through the JNI invocation interface. See AndroidRuntime.cpp in frameworks/base/.
- Do you have a tutorial launch an app in the terminal adb: bytecode file > dex file > app launch in Dalvik => and see the result in adb ?
- See 'hello-world.html' in the dalvik/docs directory (linked above).
- Is there a profiler inside Dalvik, which enable us to follow each step in the dalvik execution ?
- You could turn on LOG_INSTR to see each instruction as it is executed. This results in a rather dramatic amount of logging. If you try to do this on a device you will overrun the 64KB kernel log buffer pretty quickly and drop lots of stuff, so it's really only suitable for a 'desktop' build (e.g. sim-eng).
- Also, Dalvik does include instrumentation to allow for tracing and profiling. See http://elinux.org/Android_Tools#traceview
JIT
As of version 2.2 (Froyo), Dalvik includes a Just-In-Time compiler (or JIT).
- See A JIT Compiler for Android's Dalvik VM - video of presentation by Ben Cheng and Bill Buzbee at Google IO, 2010
The Dalvik JIT, as of version 2.2, is a 'trace-granularity JIT', which means that it compiles individual code fragments that it discovers at runtime to be 'hot spots'. (That is, it does notcompile whole methods.) The Dalvik bytecode interpreter is constantly profiling the code it is executing, and when a piece of code is determined to be running a lot, it is passed to a compiler to turn into native code. Several optimizations may be performed in this process. This code is then executed instead of the bytecode, for future runs through this section of the software.
The memory overhead of the JIT is reported to be between 100K to 200K per application.The ratio of code size between native instructions and DEX byte codes in one example give (see slide 22 of the presentation) was 7.7 to 1. That is, native instructions take approximately 8 times as much space as DEX byte codes do to perform the same operations.
Relationship to Java
Because Dalvik is not referred to as a Java Virtual Machine it does not utilize the branding of 'Java'. Also, it does not execute Java bytecodes. Hence, Google can ignore licensing issues withSun or Oracle, with regards to Java.
However, a Java compiler and set of class libraries are required in order to create a Dalvik program.
Doom 2 machine gun. As of March 2010, only the Sun JDK, version 1.5 is supported for building the Android system and add-on Android applications.
Dalvik on other platforms
- Myriad Alien Dalvik - an implementation of the Dalvik VM for other platforms (demonstrated first on Meego)
Debugging the VM
There are a number of properties you can set, to control operation of the VM and allow for debugging various aspectsof the system:
See http://netmite.com/android/mydroid/dalvik/docs/embedded-vm-control.html
(Note that this is in <aosp-root>/dalvik/docs, along with a whole bunch of other fileswith information about Dalvik.)
this mentions a number of features you can control with properties, including:
- checkjni - various checks when JNI is used
- enableassertions - enable assertions in the VM code
- verify-bytecode - whether to perform bytecode verification
- execution-mode - whether to use optimized assembly or portable C code for the interpreter
- stack-trace-file - where to put stack trace data when a SIGQUIT is received
Getting stack traces
You can force the VM to dump a stack trace of all threads by sending a SIGQUIT signal. This can be done using 'kill -3 <pid>', where pid in the main dalvik process. By default, the stack trace goes to the android log,but you can have the data sent to a file (using the dalvik.vm.stack-trace-file property) instead.
Using checkJNI
CheckJNI refers to a special runtime mode of the Dalvik VM, which forces the VM to run certain checkand report problems when it sees certain errors occuring from code called via JNI.
See http://android-developers.blogspot.com/2011/07/debugging-android-jni-with-checkjni.html
Box for iPhone and iPad allows you to sync your files between any number of devices using up to 10GB of free storage. While Box offers a decidedly stripped down interface compared to some other cloud storage tools, it beats a lot of the competition by offering more storage. Iphone box for mac. You can also open any file you download in Box while using your iOS device, and there are a number of powerful syncing tools in the preferences. There are no direct upload buttons in the app other than to move or take photos and store them in the cloud, but you can connect your Box account on a desktop or laptop and start backing up files there. With a mobile-friendly interface, tools to upload and sync photos easily, and a number of other useful tools unique to the iPhone and iPad, Box is a great addition to any iOS device that does not already have a cloud storage solution in place.After installation of Box for iPhone and iPad, you'll need to register an account or log in.
Resources
- Dalvik VM Internals - video of presentation by Dan Bornstein at Google IO, 2008
- DEX file format, reverse engineered by Michael Pavone
Retrieved from 'https://elinux.org/index.php?title=Android_Dalvik_VM&oldid=66409'
What is Android?
Android is a software stack for mobile operating devices. It includes an operating system, middleware and applications.
Key Features of Android
- Application Framework
- Dalvik Virtual Machine optimized for mobile devices
- Integrated Browser based on WebKit engine
- Optimized Graphics based on the OpenGL ES 1.0 specification
- Media, Camera, Bluetooth, GPS, compass, accelerometer support
- SQLite helps in structured data storage
- Efficient development environment helped by Eclipse – ADT plugin and device emulator.
Android Architecture
Android is built on Linux. Its core system services e.g. security, memory management, network stack, driver model depends on Linux.
Online banking system project in java pdf. Android Runtime is based on highly optimized Dalvik Virtual Machine for minimal memory footprint.
Getting Started
- Download jdk at http://www.oracle.com/technetwork/java/javase/downloads/index.html
- Download Eclipse at http://www.eclipse.org/downloads/
- Download Android SDK at http://developer.android.com/sdk/index.html
- Install ADT Plugin for Eclipse at http://developer.android.com/sdk/eclipse-adt.html#installing
Launch Android SDK and AVD Manager from Eclipse Window > Android SDK and AVD Manager.
- Setup device emulators using AVD Managers