forEach lambda会导致比赛状态吗?

问题描述

我不确定lambda在实践中如何工作，我担心，因为在某些情况下，如果使用不正确，lambda可能会导致诸如ConcurrentModificationExceptions之类的错误，这似乎表明存在竞争状况.
考虑下面的代码.

I am unsure of how lambdas work in practice, and I am concerned since under certain circumstances, lambdas can result in errors such as ConcurrentModificationExceptions if you use them incorrectly, which seems to be indicative of a race condition.
Consider the code below.

private class deltaCalculator{
    Double valueA;
    Double valueB;

    //Init delta
    volatile Double valueDelta = null;

    private void calculateMinimum(List<T> dataSource){
        dataSource.forEach((entry -> {
            valueA = entry.getA();
            valueB = entry.getB();
            Double dummyDelta;

            dummyDelta = Math.abs(valueA - valueB);

            if(valueDelta == null){
                setDelta(dummyDelta);
            }else {
                setDelta((valueDelta > dummyDelta) ? dummyDelta : valueDelta);
            }
        }));
    }

    private void setDelta(Double d){
        this.valueDelta = d;
    }
}

forEach循环如何运行?是否将不同的调用传递到JVM认为合适的不同线程，从而打开了可能导致错误的最小计算的竞争条件的可能性?
如果没有，为什么forEach lambda会引发ConcurrentModificationException?

How does the forEach loop operate? Do different calls get passed to different threads where the JVM considers it appropriate, opening up the possibility of a race condition that could lead to incorrect minimum calculation?
If not, why can a forEach lambda throw a ConcurrentModificationException?

推荐答案

如果在运行for每个循环时尝试修改要迭代的集合，则会收到ConcurrentModificationException.可以完全在一个单独的线程中完成此操作，但是当您尝试在循环主体中修改集合时，更常见的情况会发生.

You'll get a ConcurrentModificationException if you try to modify the collection that you're iterating over while the for each loop runs. This could be done in a separate thread entirely, but much more commonly occurs when you try to modify the collection in the loop body.

不.上面的示例中没有发生多线程处理.

No. No multithreading is taking place in your example above.

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