CS641 MultiThreading in Java: Example of Mandelbrot Fractal Image Calculation
/**
{{{ http://code.activestate.com/recipes/577158/ (r1)
*/
//
slightly edited by Betty O’Neil
// <applet code="MandelbrotFractal"
width=800 height=600></applet>
// MandelbrotFractal.java (FB - 201003276)
// N Multi-threaded!
import java.applet.Applet;
import java.awt.*;
import javax.swing.*;
import java.awt.image.*;
import java.lang.Thread;
public class MandelbrotFractal extends Applet
{
Image img;
volatile int
pix[]; // will be shared by all
threads
int w,h,alpha;
final int maxThr = 10; // number of threads to run
// drawing area (must be xa<xb and ya<yb)
final double xa
= -2.0;
final double xb
= 1.0;
final double ya
= -1.5;
final double yb =
1.5;
public void init()
{
w=getSize().width;
h=getSize().height;
alpha=255;
pix=new int[w*h];
manfr();
img=createImage(new MemoryImageSource(w,h,pix,0,w));
}
public void manfr()
{
long startTime
= System.currentTimeMillis();
ManFrThread[]
m = new ManFrThread[maxThr];
for(int
i=0;i<maxThr;i++) {
m[i]=new ManFrThread(i);
m[i].start();
}
// wait until all threads
finished
try {
for(int
j=0;j<maxThr;j++)
m[j].join(); // wait for thread to finish (EO)
} catch (InterruptedException
ex) {
System.out.println("saw interrupt
exception");
}
// beep to prove we got here—(EO)
java.awt.Toolkit.getDefaultToolkit().beep();
// to see this output, get a
"Java Console" window from (EO)
// Java toolbar icon (also can use
its x command to clear
// the .class cache if you
recompile this program)
System.out.println("Number
of threads: " + maxThr);
long timeInMillis
= System.currentTimeMillis() - startTime;
System.out.println("Run
Time in Millis: " + timeInMillis);
}
public void paint(Graphics g)
{
g.drawImage(img,0,0,this);
}
class ManFrThread
extends Thread
{
int k;
// id number of this thread
ManFrThread(int k)
{
this.k=k;
}
public void run()
{
double x0,x,y,a,b;
int
red,green,blue;
int
i,kx,ky,kc;
int
imax=w*h;
// Each thread only
calculates its own share of pixels!
for(i=k;i<imax;i+=maxThr)
{
kx=i%w;
ky=(i-kx)/w;
a=(double)kx/w*(xb-xa)+xa;
b=(double)ky/h*(yb-ya)+ya;
x=a;
y=b;
for(kc=0;kc<256;kc++)
{
x0=x*x-y*y+a;
y=2*x*y+b;
x=x0;
if(x*x+y*y > 4)
{
// various color
palettes can be created here!
red=255-(kc%16)*16;
green=(16-kc%16)*16;
blue=(kc%16)*16;
pix[w*ky+kx]=(alpha<<24)|(red<<16)|(green<<8)|blue;
break;
}
}
}
}
}
}
Minimal HTML to run this:
<html> <body>
<applet
code="MandelbrotFractal.class"
width="300" height="150"> </applet>
</body>
</html>
