多线程操作---线程间通信封装

Future是线程与线程间通信的封装
相当于省去了一个公共的共享区static List,以及具有wait和notify通信机制
CompletionService 相当于维护了一组Future

//Future相当于static List 以及wait,notify机制的结合，用于线程间通信
class Renderer{
	private final ExecutorService exector ;
	Renderer(ExecutorService exector ){
		this.exector = exector;
	}
	void renderPage(CharSequence source){
		final List<ImageInfo> imageInfos = scanForImageInfo(source);
		CompletionService<ImageData> completionService=
				new ExecutorCompletionService<ImageData>(executor); //CompletionService维护了一个List<Future>
		for(final ImageInfo imageInfo:info)
			completionService.submit(new Callable<ImageData>() {
				public ImageData call(){
					return imageInfo.downloadImage();
				}
			});
		renderText(source);
		for(int t=0,n=info.size();t<n;t++){
			Future<ImageData> f = completionService.take();//Future避免了在外部再定义一个List,他就可以用于线程之间的通信
			ImageData imageData = f.get();
			renderImage(imageData);
		}
	}
}