multithreadingJava
我试图在我的Java Mandelbrot应用程序中实现multithreading：
这是我到目前为止：
import java.awt.Color; import java.awt.Graphics2D; import java.awt.image.BufferedImage; public class MandelbrotSet { private int numberOfIterations; private double realMin; private double realMax; private double imaginaryMin; private double imaginaryMax; private int width; private int height; public BufferedImage image; public Graphics2D imageGraphics; public MandelbrotSet() { // Set the width and the height this.width = 600; this.height = 400; image = new BufferedImage(width, height, BufferedImage.TYPE_4BYTE_ABGR); imageGraphics = image.createGraphics(); this.realMin = -2.0; this.realMax = 1; this.imaginaryMin = -1; this.imaginaryMax = 1; this.numberOfIterations = 1000; } public Complex calculateComplexNumber(int x, int y) { double realPart = realMin + x * (realMax - realMin) / (this.getWidth() - 1); double imaginaryPart = imaginaryMax - y * (imaginaryMax - imaginaryMin) / (this.getHeight() - 1); return new Complex(realPart, imaginaryPart); } public void calculateMandelbrotImagePoints() { Thread[] threads = new Thread[4]; for (int i = 0; i < maxThreads; i++) { threads[i] = new Thread(new MThread(i)); threads[i].start(); } } class MThread implements Runnable { private int i; public MThread(int i) { this.i = i; } //Method uses the thread number to draw the mandelbrot in columns public void run() { for (int x = i; x < width; x += 4) { for (int y = 0; y < height; y++) { int n = 0; Complex c = calculateComplexNumber(x, y); Complex z = c; while ((zNumber.modulusSquared() < 4.0D) && (n < numberOfIterations)) { z = z.square(); z.add(c); n++; } if (n == numberOfIterations) { imageGraphics.setColor(Color.BLACK); } else { imageGraphics.setColor(Color.getHSBColor(n / 100.0F, 1, 1)); } imageGraphics.drawLine(x,y,x,y); } } } } } 出现的问题是，在绘制图像时，图像中会显示不正确的像素：
当我检查线程时，例如：
threads[i].isAlive();
图像似乎成功显示，但图像需要更长的时间（最多3倍）才能渲染。
我想知道两件事。
-
我哪里错了？
-
将Mandelbrots绘制到
BufferedImage进行大量迭代（> 1000）的最佳方法是什么？
我希望他的是@Michael Chang所暗示的。 我调整了代码以在band中呈现。
请注意，我无法对此进行测试。 我不熟悉Java图形。
import java.awt.Color; import java.awt.Graphics2D; import java.awt.image.BufferedImage; public class MandelbrotSet { private int numberOfIterations; private double realMin; private double realMax; private double imaginaryMin; private double imaginaryMax; private int width; private int height; public BufferedImage image; public Graphics2D imageGraphics; static final int nThreads = 4; public MandelbrotSet(int width, int height) { // Set the width and the height this.width = width; this.height = height; image = new BufferedImage(width, height, BufferedImage.TYPE_4BYTE_ABGR); imageGraphics = image.createGraphics(); this.realMin = -2.0; this.realMax = 1; this.imaginaryMin = -1; this.imaginaryMax = 1; this.numberOfIterations = 1000; } public Complex calculateComplexNumber(int x, int y) { double realPart = realMin + x * (realMax - realMin) / (width - 1); double imaginaryPart = imaginaryMax - y * (imaginaryMax - imaginaryMin) / (height - 1); return new Complex(realPart, imaginaryPart); } public void calculateMandelbrotImagePoints() { Thread[] threads = new Thread[nThreads]; int bandHeight = height / nThreads; for (int i = 0; i < nThreads; i++) { BufferedImage band = new BufferedImage(width, bandHeight, BufferedImage.TYPE_4BYTE_ABGR); threads[i] = new Thread(new MThread(band, i * bandHeight, bandHeight)); threads[i].start(); } } class MThread implements Runnable { final BufferedImage band; final Graphics2D g; final int top; final int height; private MThread(BufferedImage band, int top, int height) { this.band = band; g = band.createGraphics(); this.top = top; this.height = height; } @Override public void run() { for (int x = 0; x < width; x++) { for (int y = top; y < top + height; y++) { int n = 0; Complex c = calculateComplexNumber(x, y); Complex z = c; while ((z.times(z).mod() < 4.0D) && (n < numberOfIterations)) { z = z.times(z).plus(c); n++; } if (n == numberOfIterations) { g.setColor(Color.BLACK); } else { g.setColor(Color.getHSBColor(n / 100.0F, 1, 1)); } g.drawLine(x, y-top, x, y-top); } } // Do somehing to merge this band ino the main one. // Not familiar with java graphics so this may be wrong. imageGraphics.drawImage(band, null, 0, top); } } }
绘图不是线程安全的，因此无法从多个线程绘制相同的{screen，image，whatever}。 这些行之间可能会中断您的线程（即可能发生上下文切换）：
imageGraphics.setColor(Color.getHSBColor(n / 100.0F, 1, 1)); } imageGraphics.drawLine(x,y,x,y);
一种选择是为每个线程提供其自己的图像（例如，图像的四分之一作为图块）以进行绘制，然后在最后将图像绘制在一起。
绘图不是线程安全的 – 一个线程可以重绘另一个线程的结果。
您可以使用volatile关键字创建二维结果数组，表示结果像素。 线程可以保存到此数组而不会发生冲突，并且当数组填满（线程结束，您可以使用.join（）方法）时，您可以立即绘制所有内容。
要解决问题，请更改
if (n == numberOfIterations) { imageGraphics.setColor(Color.BLACK); } else { imageGraphics.setColor(Color.getHSBColor(n / 100.0F, 1, 1)); } imageGraphics.drawLine(x,y,x,y);
至：
synchronized(MandelbrotSet.this) { if (n == numberOfIterations) { imageGraphics.setColor(Color.BLACK); } else { imageGraphics.setColor(Color.getHSBColor(n / 100.0F, 1, 1)); } imageGraphics.drawLine(x,y,x,y); }
这将防止在更新映像期间发生线程冲突，但仍允许您在多核系统上寻求并发计算性能提升。