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<TITLE>Writing Advanced Applications, Chapter 8: Performance Features and Tools</TITLE>
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<FONT SIZE="-1"><A HREF="/developer/onlineTraining/index.html">Training Index</A></FONT>
<H2>Writing Advanced Applications<BR>
<FONT SIZE="3">Chapter 8 Continued: Performance Features and Tools</FONT></H2>
<FONT SIZE="-1">[<A HREF="conpool.html"><<BACK</A>] [<A HREF="index.html#contents">CONTENTS</A>] [<A HREF="perf3.html">NEXT>></A>]</FONT></DIV>
<P>
The new Java<FONT SIZE="-2"><SUP>TM</SUP></FONT> Virtual Machines (VMs)
have features to increase performance, and you can use a number
of tools to increase application performance or reduce the size of
generated class files. Such features and tools improve the
performance of your application with little or no change required to
your application.
<UL>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">
<A HREF="#vm">Java VM Features</A></FONT>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">
<A HREF="#jit">Just-In-Time Compilers</A></FONT>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">
<A HREF="#3rd">Third-Party Tools</A></FONT>
</UL>
<HR>
<A NAME="vm"></A>
<H3>Java VM Features</H3>
The Java® 2 Plaftform release has
introduced many performance improvements over previous
releases, including faster memory allocation, reduction of class sizes,
improved garbage collection, streamlined monitors and a built-in JIT
as standard.
When using the new Java 2 VM straight out of the box you will see an
improvement, however by understanding how the speed-ups work you can tune
your application to squeeze out every last bit of performance.
<P>
<H4>Method Inlining</H4>
The Java 2 release of the Java VM automatically inlines simple methods at
runtime.
In an un-optimized Java VM, every time a new method is called, a new
stack frame is created. The creation of a new stack frame requires additional
resources as well as some re-mapping of the stack, the end result
is that creating new stack frames incurs a small overhead.
<p>
Method inlining increases performance by reducing the number
of method calls your program makes.
The Java VM inlining code inlines methods that return constants or only access
internal fields.
To take advantage of method inlining you can do one of two things. You
can either make a method look attractive to the VM to inline or
manually inline a method if it doesn't break your object model. Manual inlining
in this context means simply moving the code from a method into the method
that is calling it.
<p>
Automatic VM inlining is illustrated using the following small example:
</FONT>
<PRE>
public class InlineMe {
int counter=0;
public void method1() {
for(int i=0;i<1000;i++)
addCount();
System.out.println("counter="+counter);
}
public int addCount() {
counter=counter+1;
return counter;
}
public static void main(String args[]) {
InlineMe im=new InlineMe();
im.method1();
}
}
</PRE>
<FONT FACE="Verdana, Arial, Helvetica, sans-serif">
In the current state the <CODE>addCount</CODE> method doesn't look very
attractive to the inline detector in the VM because the <CODE>addCount</CODE>
method returns a value. To find out if this method is inlined, run the
compiled example with profiling enabled:
</FONT>
<PRE>
java -Xrunhprof:cpu=times InlineMe
</PRE>
<FONT FACE="Verdana, Arial, Helvetica, sans-serif">
This generates a <CODE>java.hprof.txt</CODE> output file. The top ten methods
will look similar to this:
</FONT>
<PRE>
<FONT SIZE="-1">
CPU TIME (ms) BEGIN (total = 510)
Thu Jan 28 16:56:15 1999
rank self accum count trace method
1 5.88% 5.88% 1 25 java/lang/Character.
<clinit>
2 3.92% 9.80% 5808 13 java/lang/String.charAt
3 3.92% 13.73% 1 33 sun/misc/
Launcher$AppClassLoader.
getPermissions
4 3.92% 17.65% 3 31 sun/misc/
URLClassPath.getLoader
5 1.96% 19.61% 1 39 java/net/
URLClassLoader.access$1
6 1.96% 21.57% 1000 46 InlineMe.addCount
7 1.96% 23.53% 1 21 sun/io/
Converters.newConverter
8 1.96% 25.49% 1 17 sun/misc/
Launcher$ExtClassLoader.
getExtDirs
9 1.96% 27.45% 1 49 java/util/Stack.peek
10 1.96% 29.41% 1 24 sun/misc/Launcher.<init>
</FONT>
</PRE>
<FONT FACE="Verdana, Arial, Helvetica, sans-serif">
If you change the <CODE>addCount</CODE> method to no longer return a value,
the VM will inline it for you at runtime. To make the code inline friendly
replace the <CODE>addCount</CODE> method with the following:
</FONT>
<PRE>
public void addCount() {
counter=counter+1;
}
</PRE>
<FONT FACE="Verdana, Arial, Helvetica, sans-serif">
And run the profiler again:
</FONT>
<PRE>
java -Xrunhprof:cpu=times InlineMe
</PRE>
<FONT FACE="Verdana, Arial, Helvetica, sans-serif">
This time the <CODE>java.hprof.txt</CODE> output should look different.
The <CODE>addCount</CODE> method has gone. It has been inlined!
</FONT>
<PRE>
<FONT SIZE="-1">
CPU TIME (ms) BEGIN (total = 560)
Thu Jan 28 16:57:02 1999
rank self accum count trace method
1 5.36% 5.36% 1 27 java/lang/
Character.<clinit>
2 3.57% 8.93% 1 23 java/lang/
System.initializeSystemClass
3 3.57% 12.50% 2 47 java/io/PrintStream.<init>
4 3.57% 16.07% 5808 15 java/lang/String.charAt
5 3.57% 19.64% 1 42 sun/net/www/protocol/file/
Handler.openConnection
6 1.79% 21.43% 2 21 java/io/InputStreamReader.fill
7 1.79% 23.21% 1 54 java/lang/Thread.<init>
8 1.79% 25.00% 1 39 java/io/PrintStream.write
9 1.79% 26.79% 1 40 java/util/jar/
JarFile.getJarEntry
10 1.79% 28.57% 1 38 java/lang/Class.forName0
</FONT>
</PRE>
<FONT FACE="Verdana, Arial, Helvetica, sans-serif">
<H4>Streamlined synchronization</H4>
Synchronized methods and objects have until Java 2 always incurred
an additional performance hit as the mechanism used to implement the locking
of this code used a global monitor registry which was only single threaded
in some areas such as searching for existing monitors. In the Java 2
release, each thread has a monitor registry and so many of the existing
bottlenecks have been removed.
<P>
If you have previously used other locking mechanisms because of the
performance hit with synchronized methods it is now worthwhile re-visiting
this code and incorporating the new Java 2 streamlined locks.
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