Download The Android Runtime Environment

The Android Runtime
Environment
A quick, guided tour through the VM and the Core Libraries
Jörg Pleumann
Noser Engineering AG, Winterthur
8801
The Android Runtime Environment
AGENDA
OVERVIEW
VIRTUAL MACHINE
CORE LIBRARIES
SUMMARY
2
The Android Runtime Environment
Overview (I)
What is Android?
Not (just) a single mobile phone
A complete software stack for mobile devices
Kernel, middleware, and basic applications
Competes with Windows Mobile, Symbian etc.
Android is open- source
Free beer – no license fees
Free speech – no strings attached
Apache 2 license where possible
Open Handset Alliance (OHA)
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The Android Runtime Environment
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Overview (II)
Technical cornerstones
Linux- Kernel
Java programming language
Virtual machine (that is not a JVM)
Application framework
How does that
all fit together?
The Android Runtime Environment
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The Android Runtime Environment
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Dalvik VM (I)
Bytecode interpreter for mobile systems
Slow CPU (250- 500 MHz)
Little RAM (≥ 64 MB)
No swap space
Battery- powered
Should support multiple instances
Efficiency is critical
CPU / battery
Memory
Let's party like
it's 1999... ;- )
The Android Runtime Environment
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Dalvik VM (II)
Traditional JVM: Modified stack machine
Operands and results on a stack
Additional local variables
Interpreter (highly simplified)
while (true) {
char c = fetchAndDecode();
switch (c) {
case '#': doPush(getNumber());
case '+': doAdd();
case '-': doSub();
...
}
}
Dispatch means overhead, so avoid it
break;
break;
break;
The Android Runtime Environment
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Dalvik VM (III)
Dalvik VM: Register machine
All temporary values in registers
Implicit invocation stack
Custom instruction set
Higher semantic density of code
Less instructions do the same job
New instructions for problem cases
Very efficient interpreter
Can you give
an example?
The Android Runtime Environment
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Instruction set (I)
Ex ample 1: Hello, world!
System.out.println("Hallo Welt!");
JVM byte code
getstatic java.lang.System.out Ljava/io/PrintStream;
ldc "Hallo Welt!"
invokevirtual java/io/PrintStream/println(L...;)V
return
DVM byte code
sget-object v0, java.lang.System.out Ljava/io/PrintStream;
const-string v1, "Hallo Welt!"
invoke-virtual {v0, v1}, java/io/PrintStream/println(L...;)V
return-void
The Android Runtime Environment
Instruction set (II)
Ex ample 2: A simple loop over an array
public static long sumArray(int[] arr) {
long sum = 0;
for (int i : arr) {
sum += i;
}
return sum;
}
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The Android Runtime Environment
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Instruction set (III)
JVM byte code
000b:
000d:
000f:
0012:
0013:
0015:
0016:
0018:
0019:
001b:
001c:
001d:
001e:
0021:
iload 05
iload 04
if_icmpge 0024
aload_3
iload 05
iaload
istore 06
lload_1
iload 06
i2l
ladd
lstore_1
iinc 05, #+01
goto 000b
30% less instructions
in average case
DVM byte code
0007:
0009:
000b:
000c:
000d:
000f:
if-ge v0, v2, 0010
aget v1, v8, v0
int-to-long v5, v1
add-long/2addr v3, v5
add-int/lit8 v0, v0, #int 1
goto 0007
The Android Runtime Environment
Instruction set (IV)
Ex ample 3: Initializing an array
public class Demo {
private static final char[] DATA = {
'N','o','s','e','r',
'k','n','o','w','s',
'A','n','d','r','o','i','d'
};
}
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The Android Runtime Environment
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Instruction set (V)
JVM byte code
0000:
0002:
0004:
0005:
0006:
0008:
005e:
005f:
0061:
0063:
0064:
0067:
bipush 17
newarray char
dup
iconst_0
bipush 78
castore
…
dup
bipush 16
bipush 100
castore
putstatic DATA
return
Initializing the array
from a table in memory
(new instruction)
DVM byte code
0000:
0002:
0004:
0007:
0009:
000a:
const/16 v0, #int 17
new-array v0, v0, [C
fill-array-data v0, 0a
sput-object v0, DATA:[C
return-void
array-data (21 units)
'N', 'o', 's', 'e', 'r' ...
The Android Runtime Environment
Binary (I)
Class files don't work (obviously)
Dalvik Executable Format (DEX)
Size reduction
Less instructions (as shown)
Multiple classes in one DEX file
Shared constant pools
No compression
Still smaller than JAR in average case
Allows to mmap() the DEX file
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The Android Runtime Environment
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Binary (II)
The big picture
Eclipse
Java
Compiler
JAR
Tool
HelloWorld.jar
Dx
Converter
Dalvik
VM
HelloWorld.jar
Hello.class
classes.dex
World.class
strings.txt
strings.txt
image.png
image.png
The Android Runtime Environment
Random other features (I)
Byte code verification
Yes, equivalent to what a JVM does
Just- in- time compilation
Not yet, but work in progress
Compacting garbage collection
No, processes usually short- lived
Java Native Interface (JNI)
Yes, native SDK to be announced
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The Android Runtime Environment
Random other features (II)
Command line interface
Yes, via the Android Debug Bridge (ADB)
Supports usual parameters
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The Android Runtime Environment
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The Android Runtime Environment
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Core libraries (I)
Set of libraries „close to“ the VM
Each device is supposed to provide them
Android framework builds upon them
Three (public) parts
Dalvik VM- specific libraries
System info, debugging, ...
Java compatibility libraries
Base and utility classes
Third- party utility libraries
Apache HttpClient 4.0
dalvik.*
java.* javax.*
org.apache.http.*
The Android Runtime Environment
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l
Fu
l
Fu
l
Fu
org.x m l.sax
org.x m l.sax .ex t
org.x m l.sax .helpers
su
pp
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d
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pp
p
su
su
java.tex t
java.util
java.util.concurrent
java.util.concurrent.atom ic
java.util.concurrent.locks
java.util.jar
java.util.logging
java.util.prefs
java.util.regex
java.util.zip
ly
ly
ly
er
javax .x m l
javax .x m l.parsers
io
rs
ve
n
org.w3c.dom
rt
Pa
ly
javax .security.auth
javax .security.auth.callbck
javax .security.auth.login
javax .security.auth.x 500
p
su
po
rt
ed
javax .crypto
javax .crypto.interfaces
javax .crypto.spec
javax .net
javax .net.ssl
javax .security.cert
javax .sql
ld
O
java.io
java.lang
java.lang.annotation
java.lang.ref
java.lang.reflect
java.m ath
java.net
java.nio
java.nio.channels
java.nio.channels.spi
java.nio.charset
java.nio.charset.spi
java.security
java.security.acl
java.security.cert
java.security.interfaces
java.security.spec
java.sql
The Android Runtime Environment
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Core Libraries (III)
Implementation (contributed largely by Noser)
1900 API classes, 3200 classes total (ex cl. Http)
Partly taken from Apache Harmony
Partly written from scratch
Optimization
java.util.regex
java.text
JNI
JNI
java.security
java.math
ICU
OpenSSL
The Android Runtime Environment
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Core Libraries (IV)
What do we have here?
Not a Micro Edition
Looks more like a desktop JRE
GUI not a concern (no AWT / Swing)
Can we be more precise?
No, Android does not follow a JSR
Mostly compatible to a subset
of J2SE 1.5 / 5.0
Mostly? Where are
the differences?
The Android Runtime Environment
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Core packages
ClassLoader based on DEX
No defineClass(byte[])
No instrumentation, byte code weaving
Thread lacks deprecated methods
No suspend(), resume(), or stop()
No exceptions, these methods are
no- ops (unfortunately)!
No SecurityManager in use
Separate processes
Each application gets a user Linux ID
Permissions in AndroidManifest.x ml
java.lang
java.net
java.io
The Android Runtime Environment
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Internationalization
Based on ICU 3.8.1
Data differs slightly from JDK
Ex pect small differences in
java.lang.Character
java.util.Locale
java.util.Formatter
Limited set of locales
Depends on what OEM / carrier selects
Don't rely on a specific locale!
java.lang
java.util
java.text
The Android Runtime Environment
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Regular expressions
Based on ICU 3.8.1
Efficient native implementation
Syntax / semantics
Differs minimally from JDK
Not all flags supported
Collisions unlikely
Caution with highly complex cases!
java.util.regex
The Android Runtime Environment
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Security
Hybrid implementation
Bouncy Castle as JCE Provider
OpenSSL for time- critical stuff
Supported algorithms
Set differs slighly from JDK
All relevant ones are there
Others via SPI
Keystore is special
Bouncy Castle (.bks) format
No Android- specific keytool
java.crypto
javax.crypto
javax.security
javax.net.ssl
The Android Runtime Environment
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Database
JDBC 2.0
SQLite driver is limited
Not all data types supported
Some ResultSet methods throw
UnsupportedOperationEx ception
Other drivers via SPI
Alternative
Classes in android.database.sqlite
Better integration with Activities and
user interface
java.sql
javax.sql
The Android Runtime Environment
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XML
DOM Level 2 Core
No XPath, XSL, ...
Roughly the state of 2001
Should be sufficient for mobile
applications (so we thought)
SAX Version 2
SAXParser and DocumentBuilder
are non- validating
Based on KXML2 (moving to Ex pat)
Other implementations via SPI
javax.xml.*
org.w3c.dom.*
org.xml.sax.*
The Android Runtime Environment
Core Libraries (V)
Portability between Android & JRE
Not a real problem
Need to be aware of the few pitfalls
Some examples for ported projects
Jetty web server
BeanShell scripting engine
…
Coming: integration with Harmony
Improved compatibility with JRE
Both projects will benefit
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Summary
Dalvik VM
Very efficient byte code interpreter
Register machine
Executes transformed Java byte code
Core Libraries
Feature- rich system library
Subset of desktop JRE 1.5
Some tiny differences
Reuse of your knowledge and tools
Thank you for
your attention!
Jörg Pleumann
Noser Engineering AG
http:/ / www.noser.com
[email protected]
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