.net并行编程

[小猪打滚]

随机产生任意个整数数组，并计算他们的方差，并把这些方差值和对应日期值转为字符串加入到一个二维数组当中。采用并行的方式进行添加，结果发现方差值有一大部分为0。请问各位高手，这是什么原因。并行方式为AdvancedFill()
代码如下：

Imports System.Threading
Public Class Form1

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim sw = Stopwatch.StartNew()
        'NormalFill()
        Dim dArr As String(,) = AdvancedFill()
        'Dim dArr As String(,) = NormalFill()
        'Dim dArr As String(,) = AdvancedFill2() '开销过大
        'Dim dArr As String(,) = Fill3()
        For i = 0 To 100
            RichTextBox1.AppendText(dArr(i, 0) & "--" & dArr(i, 1) & vbCrLf)
        Next
        RichTextBox1.AppendText("主线程运行时间：" + sw.Elapsed.ToString)
    End Sub

    Private Function NormalFill() As String(,)
        '填充一个二维数组，10000*2
        Dim arr(100000, 1) As String
        Dim rnd As New Random
        Dim ri As Date = #1/1/1991#

        For i = 0 To 100000
            arr(i, 0) = DateAdd(DateInterval.DayOfYear, i, ri).ToShortDateString
            arr(i, 1) = GetVariance(GetIntArray(rnd, 1000)).ToString
        Next
        Return arr
    End Function
    Private Function AdvancedFill() As String(,)
        Dim arr(100000, 1) As String
        Dim rnd As New Random
        Dim ri As Date = #1/1/1991#
        Parallel.For(0, 100000, Sub(i)
                                    arr(i, 0) = DateAdd(DateInterval.DayOfYear, i, ri).ToShortDateString
                                    arr(i, 1) = GetVariance(GetIntArray(rnd, 1000)).ToString
                                End Sub)
        Return arr
    End Function
    Private Function AdvancedFill2() As String(,)
        Dim arr(100000, 1) As String
        Dim rnd As New Random
        Dim ri As Date = #1/1/1991#
        Parallel.For(0, 100000, Sub(i)
                                    arr(i, 0) = DateAdd(DateInterval.DayOfYear, i, ri).ToShortDateString
                                    arr(i, 1) = GetVariance(AdvancedGetIntArray(rnd, 1000)).ToString
                                End Sub)
        Return arr
    End Function
    Private Function Fill3() As String(,)
        Dim arr(100000, 1) As String
        Dim rnd As New Random
        Dim ri As Date = #1/1/1991#
        Dim tk1 = Task.Factory.StartNew(Sub()
                                            For i = 0 To 20000
                                                arr(i, 0) = DateAdd(DateInterval.DayOfYear, i, ri).ToShortDateString
                                                arr(i, 1) = GetVariance(AdvancedGetIntArray(rnd, 1000)).ToString
                                            Next
                                        End Sub)
        Dim tk2 = Task.Factory.StartNew(Sub()
                                            For i = 20001 To 60000
                                                arr(i, 0) = DateAdd(DateInterval.DayOfYear, i, ri).ToShortDateString
                                                arr(i, 1) = GetVariance(AdvancedGetIntArray(rnd, 1000)).ToString
                                            Next
                                        End Sub)
        Dim tk3 = Task.Factory.StartNew(Sub()
                                            For i = 60001 To 100000
                                                arr(i, 0) = DateAdd(DateInterval.DayOfYear, i, ri).ToShortDateString
                                                arr(i, 1) = GetVariance(AdvancedGetIntArray(rnd, 1000)).ToString
                                            Next
                                        End Sub)
        Task.WaitAll()
        Return arr
    End Function
    '产生一个两位数以内的正整数数组
    Private Function GetIntArray(rnd As Random, len As Integer) As Integer()
        Dim result(len - 1) As Integer
        For i = 0 To len - 1
            result(i) = rnd.Next(1, 100)
        Next
        Return result
    End Function
    Private Function AdvancedGetIntArray(rnd As Random, len As Integer) As Integer()
        Dim result(len - 1) As Integer
        Parallel.For(0, len - 1, Sub(i)
                                     result(i) = rnd.Next(1, 100)
                                 End Sub)
        Return result
    End Function
    Private Function GetVariance(intArr() As Integer) As Double
        Dim mean As Double
        Dim all As Integer = 0
        For i = 0 To intArr.Length - 1
            all += intArr(i)
        Next
        mean = all / intArr.Length
        Dim variance As Double = 0
        For i = 0 To intArr.Length - 1
            variance += (intArr(i) - mean) ^ 2
        Next
        Return variance
    End Function
   
End Class

[Poopaye]

能想到的解释就是数组里所有数都是一样的 给每个过程创建一个Random试试

[小猪打滚]

每个过程都创建Random,开销太大，而且不能完全发挥Random的功用。

[Poopaye]

引用 2 楼 crxcg 的回复:

每个过程都创建Random,开销太大，而且不能完全发挥Random的功用。

不就1000个random么，有什么开销啊

[以专业开发人员为伍]

仅就 Random 来说，你可以使用统一的 Random，例如定义为

Public Shared rnd As new Random 

这样可以保证这个值使用时全局随机。