如何避免Observer模式中的冲突？

Question

这是How can an instance communicate with its instantiator?

的后续问题

如果我有以下内容，并且方法signal（）被B的2个实例同时调用，这将导致每个B调用reset（）两次冲突。我该怎么做才能解决它？

如果发生的事件仅在所有B完成重置后才会重置，则可以重置。

public class A {
    private B b[];

    public A() {
        //for loop
        b[i] = new B(this);
    }

    public void signal() {
        //tells every B to reset.
        //for loop
        b[i].reset();
    }
}

public class B {
    A creator;

    public B(A creator) {
        this.creator = creator;
    }

    public void reset() {
        //very critical operation that should not happen back to back
    }

    public void main(String[] args) {

        while(true)
            if(isBad()==true) {
                //Something bad happen. Tell A to reset everyone.
                creator.signal();
            }

   }
}