Question

I have two seperate threads:

• logicThread – for ai, movement, sprite sorting and destruction of sprites
• drawingThread – for drawing (canvas.draw())

My logic thread calls ArrayList.remove(), so I would think when the drawing thread comes to draw there could be a chance of crashing because the index no longer exists.

code sample:

drawingThread extends Thread {
    logicThread = new LogicThread;
    logicThread.start();

    public void run(){
        while(running) {
            for(int i=0; i<npc.size(); i++){
                npc.get(i).callDraw();
            }
        }
        // stop logicThread when out of gameloop
        logicThread.running = false;
}}

LogicThread extends Thread {
    public void run(){
        while(running){
            for(int i=0; i<npc.size();i++){
                if(npc.get(i).isDead()){
                    npc.remove(i);
                }
                npc.trimToSize();
            }
            Collection.sort(npc);
        }
}}

Which would be the correct way to prevent an exception, syncronized or trycatch?
Also are there any benefits from using one over the other?

synchronized(logicThread) { 
    for(int i=0; npc.size(); i++) {
        npc.callDraw(); 
}}

or

try {
    npc.callDraw();
} catch(Exception e) {}

Answer 1

Just for note: use iterators to remove items from collection:

while (it.hasNex()) {
  if(...) {
    it.remove();

Catching IndexOutOfBound exception is valid if it’s acceptable. Another way – is to create array copy in drawing thread, which will guarantee that you don’t get IndexOutOfBound. You can just add a check isDead() inside drawing loop