java - 单独列表上的 ConcurrentModificationException 不清楚

Question

在类里面我有这两种方法:

public void notifyResult(List<Road> result) {
    ArrayList<RoadOverlay> tempRoads = new ArrayList<>();

    for(Road road:result){
    // Computes and stores the overlays
    // ...
        tempRoads.add(new RoadOverlay());
    }
    //switch field when update is done
    this.positions = tempRoads;
    }
}

private void drawRoadsVO(GL gl) {
    // keep a reference on the current instance of the field 
    // to avoid concurrent modification in notifyResult
    ArrayList<RoadOverlay> positionsCopy = this.positions;
    int vertexCount = 0;
    for (RoadOverlay road : positionsCopy) { //ConcurrentModificationException here
             // ...
        }
}

两种方法都在单独的线程中运行。在渲染内部，我没有对列表进行任何更改，据我了解，我在单独的列表上工作，那么这如何产生 CME？我正在努力解决这个问题，任何线索都会受到欢迎。我尽可能避免使用同步带来的损失。

问候

编辑了代码中的注释

Answer 1

通常最好制作列表的完整副本

ArrayList<RoadOverlay> positionsCopy = new ArrayList<Integer>(this.positions);

至于ConcurrentModificationException，您的代码看起来不错，可能是您正在其他一些类方法中修改当前的this.positions？请注意，您的 this.positions 变量应声明为 volatile。

这是ArrayList迭代器的next()方法

public E next() {
    checkForComodification();
    int i = cursor;
    if (i >= size)
        throw new NoSuchElementException();
    Object[] elementData = ArrayList.this.elementData;
    if (i >= elementData.length)
        throw new ConcurrentModificationException();
    cursor = i + 1;
    return (E) elementData[lastRet = i];
}

final void checkForComodification() {
    if (modCount != expectedModCount)
       throw new ConcurrentModificationException();
}

ConcurrentModificationException 仅在列表的 elementData 结构被修改的情况下才会抛出

Structural modifications are those that change the size of the list, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results.