MutiThreading-索引超出数组异常的范围

Question

以下多线程程序在VS 2017中引发并超出范围索引异常，但我找不到任何超出范围的索引：

using System;
using System.Threading;

class Program
{
    const int n = 100;
    static int[] sum = new int[n];

    static void f(int i, int x)
    {
        sum[i] = x; // Index was outside the bounds of the array.
    }

    static void Main()
    {
        Thread[] t = new Thread[n];
        for (int i = 0; i < n; i++)
        {
            if (i >= 100)
                throw null;
            t[i] = new Thread(() => f(i,i+1));
            t[i].Start();
        }

        int summ = 0;
        for (int i = 0; i < n; i++)
        {
            t[i].Join();
            summ += sum[i];
        }
        Console.WriteLine(summ);
        Console.ReadKey();
    }   
}

怎么了？