TIJ 线程，为什么我老觉得 例程 有问题。我太SB啦还是Bruce出错了

TIJ 21.4.1 装饰性花园

Entrance.run()方法，++number时，作者进行了同步，而且，还专门注释说“Increase number(synchronized increase)”。我认为，此处根本无需同步，因为，对于每个 Entrance对象，肯定都有自己的 number 域，这个 number 域除了 Entrance对象以外，根本没有其他线程，需要修改它。每个Entrance对象修改自己的 number，各个对象间互不打扰

即使，在其他线程（即main线程）OrnamentalGarden调用了Entrance.sumEntrances()（从而调用了Entrance.getValue()），这也是 Entrance.run()线程完成后才调用的，所以，顶多
Entrance.getValue()同步下可以理解

有人有同感嘛？难道我SB啦，或者Bruce出错了

package tij4.concurrency;

//: concurrency/OrnamentalGarden.java
import static net.mindview.util.Print.print;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

class Count {
	private int count = 0;
	private Random rand = new Random(47);

	// Remove the synchronized keyword to see counting fail:
	public synchronized int increment() {
		int temp = count;
		if (rand.nextBoolean()) // Yield half the time
			Thread.yield();
		return (count = ++temp);
	}

	public synchronized int value() {
		return count;
	}
}

class Entrance implements Runnable {
	private static Count count = new Count();
	private static List<Entrance> entrances = new ArrayList<Entrance>();
	private int number = 0;
	// Doesn't need synchronization to read:
	private final int id;
	private static volatile boolean canceled = false;

	// Atomic operation on a volatile field:
	public static void cancel() {
		canceled = true;
	}

	public Entrance(int id) {
		this.id = id;
		// Keep this task in a list. Also prevents
		// garbage collection of dead tasks:
		entrances.add(this);
	}

	public void run() {
		while (!canceled) {
			synchronized (this) {
				++number;
			}
			print(this + " Total: " + count.increment());
			try {
				TimeUnit.MILLISECONDS.sleep(100);
			} catch (InterruptedException e) {
				print("sleep interrupted");
			}
		}
		print("Stopping " + this);
	}

	public synchronized int getValue() {
		return number;
	}

	public String toString() {
		return "Entrance " + id + ": " + getValue();
	}

	public static int getTotalCount() {
		return count.value();
	}

	public static int sumEntrances() {
		int sum = 0;
		for (Entrance entrance : entrances)
			sum += entrance.getValue();
		return sum;
	}
}

public class OrnamentalGarden {
	public static void main(String[] args) throws Exception {
		ExecutorService exec = Executors.newCachedThreadPool();
		for (int i = 0; i < 5; i++)
			exec.execute(new Entrance(i));
		// Run for a while, then stop and collect the data:
		TimeUnit.SECONDS.sleep(3);
		Entrance.cancel();
		exec.shutdown();
		if (!exec.awaitTermination(250, TimeUnit.MILLISECONDS))
			print("Some tasks were not terminated!");
		print("Total: " + Entrance.getTotalCount());
		print("Sum of Entrances: " + Entrance.sumEntrances());
	}
}