java开发工作中对InheritableThreadLocal使用思考

/**
 * 测试线程池下InheritableThreadLocal线程变量失效的场景
 */
public class TestInheritableThreadLocal {
    private static final InheritableThreadLocal<String> threadLocal = new InheritableThreadLocal<>();
    // 固定大小的线程池，保证线程复用
    private static final ExecutorService executorService = Executors.newFixedThreadPool(1);
    public static void main(String[] args) {
        threadLocal.set("main线程 变量1");
        // 正常取到 main线程 变量1
        executorService.execute(() -> System.out.println(threadLocal.get()));
        threadLocal.set("main线程 变量2");
        // 线程复用再取还是 main线程 变量1
        executorService.execute(() -> System.out.println(threadLocal.get()));
    }
}

public class InheritableThreadLocal<T> extends ThreadLocal<T> {
    /**
     * 当子线程被创建时，通过该方法来初始化子线程中线程变量的值，
     * 这个方法在父线程中被调用，并且在子线程开启之前。
     * 
     * 通过重写这个方法可以改变从父线程中继承过来的值。
     *
     * @param parentValue the parent thread's value
     * @return the child thread's initial value
     */
    protected T childValue(T parentValue) {
        return parentValue;
    }
    ThreadLocalMap getMap(Thread t) {
       return t.inheritableThreadLocals;
    }
    void createMap(Thread t, T firstValue) {
        t.inheritableThreadLocals = new ThreadLocalMap(this, firstValue);
    }
}

    public Thread(ThreadGroup group, String name) {
        init(group, null, name, 0);
    }

/**
 * @param inheritThreadLocals 为ture，代表是为 包含可继承的线程变量 的线程进行初始化
 */
private void init(ThreadGroup g, Runnable target, String name,
                  long stackSize, AccessControlContext acc,
                  boolean inheritThreadLocals) {
    ...
    if (inheritThreadLocals && parent.inheritableThreadLocals != null)
        // 注意这里创建子线程的线程变量
        this.inheritableThreadLocals =
            ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
    ...
}

    private ThreadLocalMap(ThreadLocalMap parentMap) {
        Entry[] parentTable = parentMap.table;
        int len = parentTable.length;
        setThreshold(len);
        table = new Entry[len];
        for (int j = 0; j < len; j++) {
            Entry e = parentTable[j];
            if (e != null) {
                @SuppressWarnings("unchecked")
                ThreadLocal<Object> key = (ThreadLocal<Object>) e.get();
                if (key != null) {
                    // 注意！！！ 这里调用了childValue方法
                    Object value = key.childValue(e.value);
                    Entry c = new Entry(key, value);
                    int h = key.threadLocalHashCode & (len - 1);
                    while (table[h] != null)
                        h = nextIndex(h, len);
                    table[h] = c;
                    size++;
                }
            }
        }
    }