ThreadLocal的initialValue方法是怎样保证同步的

[leisore]

没明白ThreadLocal的initialValue方法是怎样保证同步的，测试程序如下，确实每个线程都有一个本地的副本
但是各个线程第一次调用get或set的时候，initialValue方法是怎样保证同步的呢？如蓝色部分

/*
 * file: ThreadLocalDemo.java
 * class: ThreadLocalDemo
 *
 * description: 
 *
 * @author:  leisore
 * @version: V1.0.0
 */
package cn.leisore.daily._2011_06_20;

import java.lang.reflect.Array;
import java.util.Set;
import java.util.TreeSet;

// ID counter, per id per thread
class ID {
	// private static final ThreadLocal<Integer> threadLocal = new
	// ThreadLocal<Integer>() {// 1
	private final ThreadLocal<Integer> threadLocal = new ThreadLocal<Integer>() {
		int initId = 0;

		@Override
		protected Integer initialValue() {
			return initId = initId + 1;
		}
	};

	public ID() {
		// private ID() {
	}

	// public static final int id() {//1
	public final int id() {
		return threadLocal.get();
	}
}

public class ThreadLocalDemo {
	public static void main(String[] args) {

		final ID id = new ID();

		final Thread[] threadArr = new Thread[10];
		@SuppressWarnings("unchecked")
		final Set<Integer>[] threadIdSetArr = (Set<Integer>[]) Array
				.newInstance(Set.class, threadArr.length);

		for (int i = 0, j = threadArr.length; i < j; i++) {
			final int threadIndex = i;
			threadIdSetArr[threadIndex] = new TreeSet<Integer>();
			threadArr[i] = new Thread(String.valueOf(threadIndex)) {
				int myIndex = threadIndex;

				@Override
				public void run() {
					for (int k = 0; k < 100; k++) {
						threadIdSetArr[myIndex].add(id.id());
					}
				}
			};
		}

		// start
		for (Thread t : threadArr) {
			t.start();
		}

		// wait until all were done
		for (Thread t : threadArr) {
			try {
				t.join();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}

		for (int i = 0, j = threadIdSetArr.length; i < j; i++) {
			System.out.println(String.format("Thread %d: %s", i,
					threadIdSetArr[i].toString()));
		}
	}
}
输出：
/*
Thread 0: [1]
Thread 1: [6]
Thread 2: [2]
Thread 3: [7]
Thread 4: [3]
Thread 5: [8]
Thread 6: [4]
Thread 7: [9]
Thread 8: [5]
Thread 9: [10]
*/

[leisore]

颜色没显示出来：
public final int id() {
return threadLocal.get();
}
和
threadIdSetArr[myIndex].add(id.id());

[leisore]

嗯，比较了一下1.5和1.6的doc中例子
1.5使用了synchronized，而1.6使用了原子变量
看来initialValue方法确实需要同步，以确保各线程可以得到正确的初始值
看看大家还有什么其他的结论没，明晚结贴
我的例子没有测出来，是机器太差了么