一个用来测量时间的类,比较精确._测量时间类-优快云博客

博客展示了一个名为StopWatch的类，通过导入系统相关命名空间，利用DllImport调用Kernel32.dll中的函数实现性能计时。该类有开始、停止计时及计算持续时间的方法，最后通过实例化该类对一段代码进行计时并计算每次迭代的时间。

Imports System
Imports System.ComponentModel
Imports System.Runtime.InteropServices

Public Class StopWatch

    <DllImport("Kernel32.dll")> _
    Shared Function QueryPerformanceCounter(ByRef lpPerformanceCount As Long) As Boolean
    End Function

    <DllImport("Kernel32.dll")> _
    Shared Function QueryPerformanceFrequency(ByRef lpFrequency As Long) As Boolean
    End Function

    Private start As Long
    Private stops As Long
    Private frequency As Long
    Private Const multiplier As Decimal = 1000000000.0

    Public Sub New()
        If QueryPerformanceFrequency(frequency) = False Then
            Throw New Win32Exception
        End If
    End Sub

    Public Sub Starts()
        QueryPerformanceCounter(start)
    End Sub

    Public Sub Parse()
        QueryPerformanceCounter(stops)
    End Sub

    Public Function Duration(ByVal iterations As Integer) As Double
        Return (((CType((stops - start), Double) * CType(multiplier, Double)) _
            / CType(frequency, Double)) / iterations)
    End Function
End Class

Dim mTimer As New StopWatch
'Measure without boxing
mTimer.Starts()

For i = 0 To 1000000000.0
'do some work to time
Next
mTimer.Parse()
'Calculate time per iteration in nanoseconds
dim result as decimal = mTimer.Duration(i)