stopwatch.vb

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Public Class Stopwatch
    'Code-timing class by Alastair Dallas 11/25/02
    'Based on Microsoft KB Article 172338 and 306978
    '
    'Use Kernel32 functions for near-microsecond timing of processes
    '
    'Usage:
    '
    '       Dim swatch as New Stopwatch("My process")
    '       ...perform My process...
    '       swatch.ReportToConsole()
    '       
    '       Output: "My process (0.332131039000767 seconds)"
    '
    '   Alternative:
    '
    '       Dim firstResult, secondResult as Double
    '       Dim swatch as New Stopwatch()
    '       ...perform process...
    '       swatch.Done()
    '       firstResult = swatch.ElapsedTime()
    '       swatch.Start()
    '       ...more process work...
    '       swatch.Done()
    '       secondResult = swatch.ElapsedTime()
    '       Console.WriteLine("First took {0} seconds and Second took {1} seconds.", 
    '           firstResult, secondResult)
    '
    '       Output: "First took 0.0131530683368976 seconds and Second took 8.8372527793337 seconds."

    Declare Function QueryPerformanceCounter Lib "Kernel32" (ByRef X As Long) As Short
    Declare Function QueryPerformanceFrequency Lib "Kernel32" (ByRef X As Long) As Short

    Private _start As Long
    Private _end As Long
    Private _freq As Long
    Private _overhead As Long
    Private _desc As String

    Public Sub New()
        Me.New("")
    End Sub

    Public Sub New(ByVal description As String)
        If (QueryPerformanceCounter(_start) = 0) Then
            Throw New StopwatchException()
        End If
        If (QueryPerformanceCounter(_end) = 0) Then
            Throw New StopwatchException()
        End If
        ' calculate the time just to call start and end
        _overhead = (_end - _start)
        Me.Start(description)
    End Sub

    Public Sub Start(Optional ByVal description As String = "")
        _desc = description
        QueryPerformanceFrequency(_freq)
        _end = 0
        If (QueryPerformanceCounter(_start) = 0) Then
            Throw New StopwatchException()
        End If
    End Sub

    Public Function Done() As Double
        If (QueryPerformanceCounter(_end) = 0) Then
            Throw New StopwatchException()
        End If
        Return Me.ElapsedTime()
    End Function

    Public Function ElapsedTime() As Double
        If (_end = 0) Then
            Dim _now As Long
            If (QueryPerformanceCounter(_now) = 0) Then
                Throw New StopwatchException()
            End If
            Return (((_now - _start) - _overhead) / _freq)
        End If
        Return (((_end - _start) - _overhead) / _freq)
    End Function

    Public Sub ReportToConsole()
        If (_end = 0) Then Me.Done()
        Console.WriteLine(_desc & " ({0} seconds)", Me.ElapsedTime())
    End Sub
End Class

Public Class StopwatchException
    Inherits System.ApplicationException

    Overrides ReadOnly Property Message() As String
        Get
            Return "Stopwatch: QueryPerformanceCounter[Kernel32] returned 0"
        End Get
    End Property
End Class