JAVA编程思想第四版-多线程的练习答案之练习13

最新推荐文章于 2019-04-12 23:26:40 发布

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本文介绍了一个基于Java实现的串号生成器SerialNumberGenerator及其检测重复串号的SerialNumberChecker类。通过使用volatile关键字和synchronized关键字确保线程安全，并利用CircularSet类存储已生成的串号来检测重复项。

package exercise.exercise13;

public class SerialNumberGenerator {
	private static volatile int serialNumber = 0;
	public static int nextSerialNumber(){
		return serialNumber++;
	}
}

package exercise.exercise13;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

class CircularSet {
	private int[] array;
	private int len;
	private int index = 0;

	public CircularSet(int size) {
		array = new int[size];
		len = size;

		for (int i = 0; i < size; i++) {
			array[i] = -1;
		}
	}

	public synchronized void add(int i) {
		array[index] = i;
		index = ++index % len;
	}

	public synchronized boolean contains(int val) {
		for (int i = 0; i < len; i++) {
			if (array[i] == val) {
				return true;
			}
		}
		return false;
	}
}

public class SerialNumberChecker {
	private static final int SIZE = 10;
	private static CircularSet serials = new CircularSet(1000);
	private static ExecutorService exec = Executors.newCachedThreadPool();

	static class SerialChecker implements Runnable {
		public void run() {
			while (true) {
				synchronized (SerialNumberGenerator.class) {
					int serial = SerialNumberGenerator.nextSerialNumber();
					if (serials.contains(serial)) {
						System.out.println("Duplicate: " + serial);
						System.exit(0);
					}
					serials.add(serial);
				}
			}
		}
	}

	public static void main(String[] args) throws Exception {
		for (int i = 0; i < SIZE; i++) {
			exec.execute(new SerialChecker());
			if (args.length > 0) {
				TimeUnit.SECONDS.sleep(new Integer(args[0]));
				System.out.println("No duplicates detected");
				System.exit(0);
			}
		}
	}
}

将SerialNumberGenerator这个类都同步了，则每次只能有一个线程去访问nextSerialNumber方法，这就保证了serialNumber++不会被其他线程打断。