root/InOutExpositor/ImageLoader.pde

// http://processing.org/discourse/yabb2/YaBB.pl?board=Integrate;action=display;num=1204990614

class ImageLoader implements Runnable {
  ImageURL img[];

  public ImageLoader() {
    img=new ImageURL[100];
  }

  public int loadImg(String _url) {
          int i;
                for (i=0; i< 100; ++i) {
                  if (img[i] == null) {
        img[i]=new ImageURL(_url);
                          return i;
                        }
                }
    println("Image Loader: request queue overflow.");
    // expand array if necessary
    //if(num==img.length) img=(ImageURL[])expand(img);
                return -1;
  }    

  public PImage getImage(int id) {
    if(img[id]==null || !img[id].loaded || img[id].error)
                        return null;
    return img[id].img;
  }

  public void delImage(int id) {
    img[id]=null;
        }

  public void run() {
    while(true) {
                        int i;
                        for (i=0; i<100; ++i) {
                    if (img[i] != null 
                                    && img[i].url != "" 
                                    && img[i].loaded == false
                                    && img[i].error  == false
                                        ) {
                                        print("Image Loader: request id:"+i+"\n");
                                        img[i].load(); // load image
                                }
                        }
                        try {
                                loadThread.sleep(500);
                        } catch(InterruptedException e) {
                                e.printStackTrace();
                        }
    }
  }
}

class ImageURL {
  PImage img;
  boolean loaded=false,error=false;
  String url="";

  public ImageURL(String _url) {
    url=_url;
  }

  void load() {
    println("nLoading image: "+url);
    img=loadImage(url);
    if(img==null) error=true;
    loaded=true;
    if(error) println("Error occurred when loading image.");
    else println("Load successful. "+
    "Image size is "+img.width+"x"+img.height+".");
  }
}