为什么List <T> .Add抛出索引超出范围异常？

Question

当我打电话给List<T>.Add(T)它时，抛出此异常：

System.IndexOutOfRangeException: Index was outside the bounds of the array.
   at System.Collections.Generic.List`1.Add(T item)
   at ConsoleApp5.Program.AddToList(Int32 seed) 

我还看到Enumerable.Any针对同一列表抛出此异常。

Answer 1

这可能是由于竞争状况引起的。如果两个或多个线程同时修改列表，则列表可能会损坏。此后，以后对该列表进行的任何操作都将失败。

这是将重现它的示例。

    static List<int> TestList;
    const int ThreadCount = 10;
    const int IterationsA = 1000;

        static int count = 0;

    static void Main(string[] args)
    {
        try
        {
            while (true)
            {
                TestList = new List<int>();
                List<Thread> threads = new List<Thread>();

                for (var x = 0; x < ThreadCount; x++)
                {
                    var t = new Thread(() => AddToList(x));
                    t.Start();
                    threads.Add(t);
                }

                foreach (var t in threads)
                    t.Join();

                var b = TestList.Any(i => i == 1);

                Console.WriteLine("Pass " + DateTime.Now.ToString("hh:mm:ss.fff"));
                count += 1;
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex);
            Console.WriteLine($"Failed after {count} attempts");
        }

        Console.ReadLine();

    }

    static void AddToList(int seed)
    {
        try
        {
            var random = new Random(seed);

            for (var x = 0; x < IterationsA; x++)

            {
                TestList.Add(random.Next());
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex);
            Console.WriteLine($"Failed after {count} attempts");
            Console.ReadLine();
        }
    }

请注意，它可能发生在第一次迭代或数千次迭代之后。