java – ThreadLocal线程安全吗？

private static final ThreadLocal threadLocalField = new ThreadLocal;

public static void getSXTransaction() {
  threadLocalField.set(new MyValue());
}

我想知道,由于java.lang.ThreadLocal #set方法中没有隐式同步,所以线程安全的保证是什么？
我知道TreadLocal类本质上是完全线程安全的,但是我无法理解它是如何实现的.

这是它的源代码：

/**
 * Sets the current thread's copy of this thread-local variable
 * to the specified value.  Most subclasses will have no need to 
 * override this method,relying solely on the {@link #initialValue}
 * method to set the values of thread-locals.
 *
 * @param value the value to be stored in the current thread's copy of
 *        this thread-local.
 */
public void set(T value) {
    Thread t = Thread.currentThread();
    ThreadLocalMap map = getMap(t);
    if (map != null)
        map.set(this,value);
    else
        createMap(t,value);
}