Synchronize the paint() method of a Java Canvas instance? - swing

Question

Basically I am running a java emulator at 60 FPS and each time the screen refreshes it draws pixels from an array and paints it to the screen. I am getting a java.util.ConcurrentModificationException i.e. the contents of the pixel array are getting modified sometime during the paint() method execution. Is there a way I can synchronize the paint method or the generatePalette method to avoid this? Or is there another/better solution?
Code:
public class LCD extends Canvas implements Runnable {
/**
*
*/
private static final long serialVersionUID = 1L;
private static final int FRAME_RATE = 1 / 60 * 1000;
private BufferedImage canvas;
private List<Pixel> pixels = new ArrayList<>();
private int tilemapStart, tilemapEnd;
private GBCpuBootRom cpu;
private GBBus bus;
public void init() {
setTileMap(bus.cpuRUnsigned8(0xFF40));
generatePalette(bus, bus.cpuRUnsigned8(0xFF40));
}
public LCD(int len, int hei, GBCpuBootRom cpu, GBBus bus) {
canvas = new BufferedImage(len,hei,BufferedImage.TYPE_INT_ARGB);
this.cpu = cpu;
this.bus = bus;
Thread t = new Thread(this);
t.start();
}
public void setTileMapExplicit(int start, int end) {
tilemapStart = start;
tilemapEnd = end;
}
public void setTileMap(int mFF40) {
/*
* Bit 3 (bit 5)
* 0: 9800 to 9BFF
* 1: 9C00 to 9FFF
*
* Bit 4 (bit 4)
* 0: 8800 to 97FF
* 1: 8000 to 8FFF
*/
if ( ((mFF40 & 0b00001000) >> 3) == 1) {
tilemapStart = 0x9C00;
tilemapEnd = 0xA000;
}
else {
tilemapStart = 0x9800;
tilemapEnd = 0x9C00;
}
}
public void paint(Graphics g) {
for(Pixel p:pixels)
try {
canvas.setRGB(p.getX(), p.getY(), p.getColor().getRGB());
}
catch(Exception e) {
/*
* If a pixel cannot be drawn
* skip it and move on to next.
*/
System.out.println("Cannot draw pixel: " + p.getX() + ", " +
p.getY());
}
draw(g);
}
private void draw(Graphics g) {
Graphics2D g2 = (Graphics2D) g;
g2.drawImage(canvas, null, null);
}
public void generatePalette(GBBus bus, int mFF40) {
int hor = 0;
int ver = 0;
int x = 0;
int y = 0;
int inc = 8;
int pixelCount = 0;
/*
* maxRowPixels
* Each tile has 64 pixels
* if 256 x 256
* maxRowPixels = 2048 (32 * 64)
* else if 160 x 144
* maxRowPixels = 1280 (20 * 64)
*/
int maxRowPixels = canvas.getWidth() == 256 ? 2048 : 1280;
Pixel[] palettes;
Palette palette = new Palette();
for(int i = tilemapStart; i < tilemapEnd; i++) {
int dataAddr = spriteAddress((mFF40 & 0b00010000) >> 4, bus.cpuRUnsigned8(i));
/*
* Read range 0 to F
* e.g.
* 08000: 08000 to 0x800F
*
* 08000, 08002, 08004, 08006,
* 08008, 0800A, 0800C, 0800D,
*/
for(int k = 0; k < 16; k = k + 2) {
int hByte = bus.cpuRUnsigned8(dataAddr + k);
int lByte = bus.cpuRUnsigned8(dataAddr + (k + 1));
palette.setHB(hByte);
palette.setLB(lByte);
palette.setXY(x, y);
palette.init();
palettes = palette.getPixels();
for(Pixel pix: palettes)
pixels.add(pix);
x += inc;
pixelCount += inc;
if(x % 8 == 0) {
x = hor;
y++;
}
/*
* 1 tile completed
* 8 x 8 = 64p
* p means pixels
*/
if(pixelCount % 64 == 0) {
hor = hor + inc;
x = hor;
y = ver;
}
if(pixelCount % maxRowPixels == 0) {
x = 0;
hor = 0;
ver = ver + inc;
y = ver;
}
}
}
}
#Override
public void run() {
Thread.currentThread();
while(true) {
cpu.compute();
pixels.clear();
init();
try {
Thread.sleep(1000);
}
catch(Exception e) {
e.printStackTrace();
}
repaint();
}
}
}
This is the exception I get at line 66 (for loop in paint() method above)
Exception in thread "AWT-EventQueue-0" java.util.ConcurrentModificationException
at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1009)
at java.base/java.util.ArrayList$Itr.next(ArrayList.java:963)
at gameboyconcept.logo.LCD.paint(LCD.java:66)