System.Collections.ArrayList.Add 在什么情况下会抛出 IndexOutOfRangeException?

问题描述

我们在生产环境中遇到了奇怪的错误，我们无法调试也无法注入日志代码.我试图弄清楚这一点，但跟踪堆栈跟踪让我感到困惑.

We are experiencing weird bug at production environment we cannot debug nor inject logging code. I am trying to figure this up but following stack trace confuse me.

System.IndexOutOfRangeException: Index was outside the bounds of the array.
   at System.Collections.ArrayList.Add(Object value)
   at ...

根据MSDN Add 方法应该只抛出 NotSupportedException.

According to the MSDN Add method should only throw NotSupportedException.

我不知道这里发生了什么.你呢?

I have no idea what's going on here. Do you?

推荐答案

归结为 List 不是线程安全的.我在使用多个线程添加项目后遍历列表时发生了IndexOutOfRangeException，没有同步.下面的代码可能会破坏项目计数并在随后迭代列表时导致 IndexOutOfRangeException，

It boils down to List not being thread safe. I have had IndexOutOfRangeException occuring when iterating over a list after adding items using multiple threads without synchronization. The code below could corrupt the items count and result in IndexOutOfRangeException while iterating the list subsequently,

List<TradeFillInfo> updatedFills = new List<TradeFillInfo>();
Parallel.ForEach (trades, (trade) =>
{
    TradeFillInfo fill = new TradeFillInfo();

    //do something

    updatedFills.Add(fill); //NOTE:Adding items without synchronization
});

foreach (var fill in updatedFills) //IndexOutOfRangeException here sometimes
{
    //do something
}

将 Add() 与 lock 语句同步将解决该问题.

Synchronizing the Add() with a lock statement will fix the issue.

lock (updatedFills)
{
    updatedFills.Add(fill);
}

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