C#中的随机数

Question

可能重复:
随机数生成器不按我计划的方式工作(C#)

我创建了一个方法,返回一个随机数:

public static int SelectRandomMachine(int max)
{
int seed = (int)DateTime.Now.Ticks;
Random rndNumber = new Random(seed);
int randMachine = rndNumber.Next(0, max);
return randMachine;
}

如果我两次调用该方法,目前它返回相同的随机数:

randM1 = SelectRandomMachine(maxNumber);
randM2 = SelectRandomMachine(maxNumber);

任何建议都将受到高度赞赏.

Answer 1

提示看看这一行:

int seed = (int)DateTime.Now.Ticks;

如果您连续两次执行该行,您认为这些值是什么？

例如:

int seed1 = (int)DateTime.Now.Ticks;
int seed2 = (int)DateTime.Now.Ticks;

// Write it out *after* executing; console output can take a while
Console.WriteLine(seed1);
Console.WriteLine(seed2);

有关解决方案和更多信息,请参阅我的随机性文章.

编辑:这是一个缺乏线程安全导致问题的快速而肮脏的例子:

using System.Collections.Generic;
using System.Threading;

class Program
{
    const int Iterations = 1000000;
    static readonly Random rng = new Random();

    static void Main(string[] args)
    {
        List<Thread> threads = new List<Thread>();
        for (int i = 0;  i < 8; i++)
        {
            Thread t = new Thread(ExerciseRandom);
            threads.Add(t);
            t.Start();
        }
        foreach (Thread t in threads)
        {
            t.Join();
        }
        Console.WriteLine(rng.Next());
        Console.WriteLine(rng.Next());
        Console.WriteLine(rng.Next());
    }

    static void ExerciseRandom()
    {
        for (int i = 0; i < Iterations; i++)
        {
            rng.Next();
        }
    }
}

我的盒子输出:

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