JDK 5 Documentation v1.1.8, Java 2 SDK 英文文档

Inner Classes Specification

Further Example: Multi-threaded task partitioning.

It is sometimes useful to parallelize a task with independent sub-tasks, by assigning each sub-task to a thread. This can make the whole task finish sooner, if multiple processors are involved. (This will be the case, if the sub- tasks perform network traffic.) In interactive Java programs, multithreading is also used to enable partial results from sub-tasks to be pushed through to the end user, while slower sub-tasks continue to grind away.

The code below (based on an example from Doug Lea) shows a very simple way to control the rendering of several pictures in such a way that each picture is delivered to a displayer as soon as it's ready, but the original requester blocks until all rendering is finished. Each sub-task is coded by an anonymous implementation of Runnable which is at the heart of each thread.

public class GroupPictureRenderer { private PictureRenderer renderer; private PictureDisplayer displayer; ... public Picture[] render(final byte[][] rawPictures) throws InterruptedException { Thread workers[] = new Thread[rawPictures.length]; final Picture results[] = new Picture[rawPictures.length]; // start one thread per rendering sub-task for (int ii = 0; ii < rawPictures.length; ii++) { final int i = ii; // capture ii for each new thread Runnable work = new Runnable() { public void run() { results[i] = renderer.render(rawPictures[i]); displayer.display(results[i]); } }; workers[i] = new Thread(work, "Renderer"); workers[i].start(); } // all threads are running; now wait for them all to finish for (int i = 0; i < workers.length; i++) workers[i].join(); // give all the finished pictures to the caller, too: return results; } }

public class GroupPictureRenderer { private PictureRenderer renderer; private PictureDisplayer displayer; ... public Picture[] render(final byte[][] rawPictures) throws InterruptedException { Thread workers[] = new Thread[rawPictures.length]; final Picture results[] = new Picture[rawPictures.length]; // start one thread per rendering sub-task for (int ii = 0; ii < rawPictures.length; ii++) { final int i = ii; // capture ii for each new thread Runnable work = new Runnable() { public void run() { results[i] = renderer.render(rawPictures[i]); displayer.display(results[i]); } }; workers[i] = new Thread(work, "Renderer"); workers[i].start(); } // all threads are running; now wait for them all to finish for (int i = 0; i < workers.length; i++) workers[i].join(); // give all the finished pictures to the caller, too: return results; } }

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Inner Classes Specification (HTML generated by dkramer on March 15, 1997)
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