Java 并发编程实战学习笔记——寻找可强化的并行性

寻找可强化的并行性

1.串行执行所有任务

代码 复制 - 运行

package net.jcip.examples; 

import java.util.*; 

/**
 * SingleThreadRendere
 * <p/>
 * Rendering page elements sequentially
 *
 * @author Brian Goetz and Tim Peierls
 */
public abstract class SingleThreadRenderer {
    void renderPage(CharSequence source) {
        renderText(source);
        List<ImageData> imageData = new ArrayList<ImageData>();
        for (ImageInfo imageInfo : scanForImageInfo(source))
            imageData.add(imageInfo.downloadImage());
        for (ImageData data : imageData)
            renderImage(data);
    } 

    interface ImageData {
    } 

    interface ImageInfo {
        ImageData downloadImage();
    } 

    abstract void renderText(CharSequence s);
    abstract List<ImageInfo> scanForImageInfo(CharSequence s);
    abstract void renderImage(ImageData i);
} 

2.并行执行页面渲染，和所有图片下载任务。

代码 复制 - 运行

package net.jcip.examples; 

import java.util.*;
import java.util.concurrent.*;
import static net.jcip.examples.LaunderThrowable.launderThrowable; 

/**
 * FutureRenderer
 * <p/>
 * Waiting for image download with \Future
 *
 * @author Brian Goetz and Tim Peierls
 */
public abstract class FutureRenderer {
    private final ExecutorService executor = Executors.newCachedThreadPool(); 

    void renderPage(CharSequence source) {
        final List<ImageInfo> imageInfos = scanForImageInfo(source);
        Callable<List<ImageData>> task =
                new Callable<List<ImageData>>() {
                    public List<ImageData> call() {
                        List<ImageData> result = new ArrayList<ImageData>();
                        for (ImageInfo imageInfo : imageInfos)
                            result.add(imageInfo.downloadImage());
                        return result;
                    }
                }; 

        Future<List<ImageData>> future = executor.submit(task);
        renderText(source); 

        try {
            List<ImageData> imageData = future.get();
            for (ImageData data : imageData)
                renderImage(data);
        } catch (InterruptedException e) {
            // Re-assert the thread's interrupted status
            Thread.currentThread().interrupt();
            // We don't need the result, so cancel the task too
            future.cancel(true);
        } catch (ExecutionException e) {
            throw launderThrowable(e.getCause());
        }
    } 

    interface ImageData {
    } 

    interface ImageInfo {
        ImageData downloadImage();
    } 

    abstract void renderText(CharSequence s); 

    abstract List<ImageInfo> scanForImageInfo(CharSequence s); 

    abstract void renderImage(ImageData i);
} 

3.并行执行页面渲染，和单个图片下载任务。

代码 复制 - 运行

package net.jcip.examples; 

import java.util.*;
import java.util.concurrent.*;
import static net.jcip.examples.LaunderThrowable.launderThrowable; 

/**
 * Renderer
 * <p/>
 * Using CompletionService to render page elements as they become available
 *
 * @author Brian Goetz and Tim Peierls
 */
public abstract class Renderer {
    private final ExecutorService executor; 

    Renderer(ExecutorService executor) {
        this.executor = executor;
    } 

    void renderPage(CharSequence source) {
        final List<ImageInfo> info = scanForImageInfo(source);
        CompletionService<ImageData> completionService =
                new ExecutorCompletionService<ImageData>(executor);
        for (final ImageInfo imageInfo : info)
            completionService.submit(new Callable<ImageData>() {
                public ImageData call() {
                    return imageInfo.downloadImage();
                }
            }); 

        renderText(source); 

        try {
            for (int t = 0, n = info.size(); t < n; t++) {
                Future<ImageData> f = completionService.take();
                ImageData imageData = f.get();
                renderImage(imageData);
            }
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        } catch (ExecutionException e) {
            throw launderThrowable(e.getCause());
        }
    } 

    interface ImageData {
    } 

    interface ImageInfo {
        ImageData downloadImage();
    } 

    abstract void renderText(CharSequence s); 

    abstract List<ImageInfo> scanForImageInfo(CharSequence s); 

    abstract void renderImage(ImageData i); 

}