在 C# 中使用线程填充随机数的数组

Question

正如在图块中所说，我正在尝试使用 16 个（在我的情况下）线程填充一个带有随机数的字节数组，现在使用一个线程填充一个包含 500000000 个字节的数组大约需要六秒半的时间线程所以逻辑说使用 16 个线程将至少快 10 倍，但后来我尝试这样做，花了 15 秒来填充它，我所做的是我给每个线程一个段来填充相同的数组

代码如下：

        static byte[] nums2 = new byte[500000000];
        static Random rnd = new Random(123);
        static void fill()
        {
            for (int i = 0; i < nums.Length; i++)
                nums[i] = (byte)rnd.Next(10);
        }

        static void fillPart(object ID)
        {
            var part = nums2.Length / Environment.ProcessorCount;
            int baseN = (int)ID * part;
            for (int i = baseN; i < baseN + part; i++)
                nums2[i] = (byte)rnd.Next(10);
            Console.WriteLine("Done! " + ID);
        }

        static void Main(string[] args)
        {
            Stopwatch watch = new Stopwatch();
            watch.Start();
            fill();
            watch.Stop();
            Console.WriteLine("it took " + watch.Elapsed);
            Console.WriteLine();

            watch.Reset();
            watch.Start();
            Thread[] threads = new Thread[Environment.ProcessorCount];
            for (int i = 0; i < Environment.ProcessorCount; i++)
            {
                threads[i] = new Thread(fillPart);
                threads[i].Start(i);
            }
            for(int i = 0; i < Environment.ProcessorCount; i++)
                threads[i].Join();

            watch.Stop();
            Console.WriteLine("it took " + watch.Elapsed);
        }
    }```
would like to understand why is it took 15 seconds or maybe what I did wrong

Answer 1

如果是我，我会：

byte[] nums = new byte[500000000];
RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
rng.GetBytes(nums);

并完成它。

如果你真的想要线程：

RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
var dop = 8;
var batchSize = 500000000 / dop;
var bigBytes = Enumerable.Range(0, dop).AsParallel().SelectMany(t => {
    var bytes = new byte[batchSize];
    rng.GetBytes(bytes); //This *IS* thread-safe
    return bytes;
}).ToArray();

但我怀疑SelectMany 和ToArray 整理到一个新数组所花费的时间可能会比单线程方法更昂贵。

Answer 2

问题是你声明了static Random rnd = new Random(int.MaxValue); 如果您在fillPart 方法中创建Random 实例，那么程序将在一秒钟内完成，所以不是Thread 的问题是rnd.Next(10)

        static void fillPart(object ID)
        {            
            Random rnd = new Random(123);

            var part = nums2.Length / Environment.ProcessorCount;
            int baseN = (int)ID * part;
            int co = 0;
            for (int i = baseN; i < baseN + part; i++)
            {
                nums2[i] = (byte)rnd.Next(10);
            }

            //Console.WriteLine("Done! " + ID + co);
        }