How To Use Virtual Memory In Visual Basic.Net

Sometimes don't you want to use ram as you go, instead of loading giant files into ram? Here is an example of how to utilize Virtual Memory in Visual Basic.


The following Visual Basic code uses the MemoryMappedFile.CreateFromFile(FileName) method, although MemoryMappedFile has other methods available, they are not available in this article. This example generates fake DNA sequences to demonstrate how to use Virtual Memory. This example is designed to work if you simply create a new Visual Basic.Net project, and replace all of Form1's code with the following code and click run:

  • Option Strict On
    Imports System
    Imports System.Text
    Imports System.IO.MemoryMappedFiles
    Public Class Form1
        'This will hold the references for the files stored in Virtual Memory
        Private Lines As New List(Of MemoryMappedFile)
        'This is used to generate random characters for the file
        Private Random As New Random(1)
        'This is used for flashing the seeking... 's flashing .'s
        Private LastSeekingString As String = Space(3)
        'this is the path to the folder where Virtual Ram files will be stored
        Private Path As String = My.Computer.FileSystem.SpecialDirectories.Desktop & "\DatFiles\"
        'A richtextbox will be used for displaying data
        Friend WithEvents RichTextBox1 As New DBRichTextBox With {.Parent = Me, .Width = 565, .BackColor = Color.FromArgb(33, 33, 33), .ForeColor = Color.White}
        'These scrollbars scroll the data offsets/line numbers
        Friend WithEvents VScrollBar1 As New VScrollBar With {.Parent = Me}
        Friend WithEvents HScrollBar1 As New HScrollBar With {.Parent = Me}
        'This aligns the blocks of data, regardless of the line numbers using the .PadRight feature later
        Dim LineLabelPadWidth As Integer = 10
        'Calculate how many lines are visible in the richtextbox
        Private ReadOnly Property MaxVisibleLines As Integer
                'Get the height of the current font
                Dim TextHieght As Integer = RichTextBox1.Font.Height
                'calculate how many lines the richtextbox can hold
                Return (RichTextBox1.ClientRectangle.Height \ TextHieght) - 2
            End Get
        End Property
        Private ReadOnly Property VisibleCharactersInLine As Integer
                Dim CharacterWidth As Integer
                'Calculate the width of a character(for monospaced font consolas, the width is half of the height)
                CharacterWidth = RichTextBox1.Font.Height \ 2
                'Calculate how many data characters are in a line
                Dim Characters As Integer = (RichTextBox1.ClientRectangle.Width \ CharacterWidth) - LineLabelPadWidth - 1
                'return the result
                Return Characters
            End Get
        End Property
    #Region "Events"
        Private Sub Form1_FormClosing(sender As Object, e As FormClosingEventArgs) Handles Me.FormClosing
            'Dispose each memorymappedfile before exiting the program
            For Each mmf As MemoryMappedFile In Lines
            If My.Computer.FileSystem.DirectoryExists(Path) Then
                'Delete the files if they exist
                My.Computer.FileSystem.DeleteDirectory(Path, FileIO.DeleteDirectoryOption.DeleteAllContents)
            End If
        End Sub
        Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
            Me.Text = "System.IO.MemoryMappedFiles.MemoryMappedFile Example"
                'Add the scroll event handler for the scrollbars
                AddHandler VScrollBar1.Scroll, AddressOf ScrollBar_Scroll
                AddHandler HScrollBar1.Scroll, AddressOf ScrollBar_Scroll
                If My.Computer.FileSystem.DirectoryExists(Path) Then My.Computer.FileSystem.DeleteDirectory(Path, FileIO.DeleteDirectoryOption.DeleteAllContents)
                'Create the directory to store the virtual memory files in
                'Disable the richtextboxes scrollbars(because we are using our own)
                RichTextBox1.ScrollBars = RichTextBoxScrollBars.None
                'make richtextbox1 readonly
                RichTextBox1.ReadOnly = True
                'Make the form double buffered
                Me.DoubleBuffered = True
                'Position all controls
                'randomize the timer
                'Create a stringbuilder reference
                Dim SB As StringBuilder
                For Line As Integer = 0 To 99 ' Generate 100 200000 Character dummy DNA data lines.
                    'Assign a new instance of stringbuilder to the reference
                    SB = New StringBuilder
                    'Generate Each Line's Data(Each line will, have its own file for VRAM
                    For LineCharacters As Integer = 0 To 199999 ' Make each line 200000 chars long
                        'Append a random character to the stringbuilder
                    'Generate a filename for the current line
                    Dim FileName As String = Path & "DataFile" & Line.ToString & ".Dat"
                    'Use a file stream to write to the file
                    Using FS As New IO.FileStream(FileName, IO.FileMode.CreateNew)
                        'convert the string into an array of byte
                        Dim Array As Byte() = Encoding.ASCII.GetBytes(SB.ToString)
                        'write the array to the stream
                        FS.Write(Array, 0, Array.Count)
                        'close the file stream
                        'Clear the array
                        Array = {}
                    End Using
                    'create a new memorymapped file, this locks the file for exclusive use with your program
                    Dim MemoryMappedFile As MemoryMappedFile = MemoryMappedFile.CreateFromFile(FileName)
                    'Add a reference to the loaded memorymapped file to the list of memorymappedfiles(one entire file per line)
                'Set Richtextbox1 to have a monospaced font
                RichTextBox1.Font = New Font("consolas", 16)
                'Since each line will be 200k Characters long, we need to set the horizontal scrollbar's maxvalue
                HScrollBar1.Maximum = 200000 - VisibleCharactersInLine + 8
                'reset the scrollpoint of hscrollbar
                HScrollBar1.Minimum = 0
                'calculate Vscrollbar's max value
                VScrollBar1.Maximum = Lines.Count - MaxVisibleLines + 8
                'reset the scrollpoint
                VScrollBar1.Minimum = 0
                ' Highlight the concatenated output of the locationstring function and the displaytext function(highlight the chromosones characters)
                HighlightChromies(locationString() & DisplayText())
            Catch ex As Exception
            End Try
        End Sub
        Private Sub Form1_SizeChanged(sender As Object, e As EventArgs) Handles Me.SizeChanged
            'reposition the controls on the form
            'reset the maximum values of the scrollbars because the size of the richtextbox changed
                VScrollBar1.Maximum = Lines.Count - MaxVisibleLines + 8
                'Each file is exactly 200000 characters long, and the scrollbar will not quite scroll to its max value(bug?), so we adjust with 8 characters
                HScrollBar1.Maximum = 200000 - VisibleCharactersInLine + 8
                '1.) Calculate the location string
                '2.) Calculate the display text
                '3.) Concatonate the result of the two
                '4.) Highlight the concatonated result of the two
                HighlightChromies(locationString() & DisplayText())
            Catch : End Try
        End Sub
        Private Sub ScrollBar_Scroll(sender As Object, e As ScrollEventArgs)
            'Choose the type of scroll event that was raised
            Select Case e.Type
                Case ScrollEventType.EndScroll
                    'If the user finished scrolling:
                    '1.) Calculate the location string
                    '2.) Calculate the display text
                    '3.) Concatonate the result of the two
                    '4.) Highlight the concatonated result of the two
                    HighlightChromies(locationString() & DisplayText())
                Case ScrollEventType.ThumbTrack
                    'The user is probably scrolling too fast
                    'to maintain good performance, so instead we just
                    'display information about
                    'the current selection
                    RichTextBox1.Text = SeekingString() & locationString()
                Case Else
                    'The user is probably holding the buttons
                    'down on the scrollbar, so we don't want to
                    'use the processor intensive highlight sub until they have finished scrolling
                    RichTextBox1.Text = SeekingString() & locationString() & DisplayText()
            End Select
        End Sub
    #End Region
    #Region "Functions"
        Private Function DisplayText() As String
            'Create a new stringbuilder
            Dim SB As New StringBuilder
            'Scroll through the visible range of lines(using the scrollbar to determine the user selection
            For I As Integer = VScrollBar1.Value To VScrollBar1.Value + MaxVisibleLines
                'Call the GetData function to create a line of data
                'Append that line of data to the stringbuilder
                SB.Append(GetData(I, HScrollBar1.Value, VisibleCharactersInLine))
            'retirm the final result, removing the last carriage return that was appended
            Return SB.ToString.Substring(0, SB.Length - 1)
        End Function
        Private Function GetData(LineNumber As Integer, Offset As Integer, Length As Integer) As String
                'Create a reference to the current line's memorymappedfile
                Dim CurrentMemoryMappedFile As MemoryMappedFile = Lines(LineNumber)
                'create an array to hold that line's bytes
                Dim Bytes(199999) As Byte
                'Create a MemoryMappedViewAccessor to load data from that file
                Using V As MemoryMappedViewAccessor = CurrentMemoryMappedFile.CreateViewAccessor
                    'Read the data into the Bytes Array
                    V.ReadArray(Of Byte)(0, Bytes, 0, 200000)
                End Using
                'Converting the bytes into a string, build a data line for display
                Return ("Line" & LineNumber.ToString & ":").PadRight(LineLabelPadWidth, " "c) & Encoding.ASCII.GetString(Bytes.ToList.GetRange(Offset, Length).ToArray) & vbCrLf
            Catch ex As Exception
                'return a line that has the error message.
                Return ("Line" & LineNumber.ToString & ":").PadRight(LineLabelPadWidth, " "c) & ex.Message & vbCrLf
            End Try
        End Function
        Public Function SeekingString() As String
            'This is purly asthetic
            'Add the appearence of animated dot dot dotting... working...
            Select Case LastSeekingString
                Case Space(3)
                    LastSeekingString = "." & Space(2)
                Case "." & Space(2)
                    LastSeekingString = ".." & Space(1)
                Case ".." & Space(1)
                    LastSeekingString = "..."
                Case "..."
                    LastSeekingString = Space(3)
                Case Else
                    LastSeekingString = Space(3)
            End Select
            Return "Seeking" & LastSeekingString
        End Function
        Private Function GetRandomGeneChar() As Char 'Function Borrowed from Reed Kimble:)
            'Randomly select one of "ACTG"
            Dim chars As String = "ATCG"
            Return chars(Random.Next(0, 4))
        End Function
        Private Function locationString() As String
            'Generate the first line displayed in the richtextbox,
            'that identifies exactly what information is being displayed.
            Return "Map coordinates[X=" & HScrollBar1.Value.ToString & ", Y=" & VScrollBar1.Value.ToString & "]" & vbCrLf
        End Function
    #End Region
    #Region "Subs"
        Private Sub DoLayout()
            'Calculate the controls locations and sizes
            RichTextBox1.Location = New Point(0, 0)
            VScrollBar1.Left = Me.ClientRectangle.Width - VScrollBar1.Width
            VScrollBar1.Height = Me.ClientRectangle.Height - HScrollBar1.Height
            HScrollBar1.Left = 0
            HScrollBar1.Width = Me.ClientRectangle.Width - VScrollBar1.Width
            HScrollBar1.Top = Me.ClientRectangle.Height - HScrollBar1.Height
            RichTextBox1.Width = Me.ClientRectangle.Width - VScrollBar1.Width
            RichTextBox1.Height = Me.ClientRectangle.Height - HScrollBar1.Height
        End Sub
        Private Sub HighlightChromies(Text As String)
            'Generating RTF is faster than setting the selection color properties :)
            'Create RTF Header
            Dim Header As String = "{\rtf1\ansi\deff0{\fonttbl{\f0\fnil\fcharset0 " & RichTextBox1.Font.FontFamily.Name & ";}}" & vbCrLf & _
             "{\colortbl ;\red0\green128\blue0;\red0\green0\blue255;\red255\green165\blue0;\red255\green0\blue0;}" & vbCrLf & _
            "\viewkind4\uc1\pard\lang1033\f0\fs" & CInt((RichTextBox1.Font.Size * 2)).ToString & " "
            'Build RTF Code to highlight all occurrences of each of the following
            Text = Text.Replace("G", "\highlight3 G\highlight0") 'g
            Text = Text.Replace("A", "\highlight1 A\highlight0") 'a
            Text = Text.Replace("C", "\highlight4 C\highlight0") 'c
            Text = Text.Replace("T", "\highlight2 T\highlight0") 't
            'replace all carriage returns with the RTF code that indicates a carriage return
            Text = Text.Replace(vbCrLf, "\par" & vbCr)
            'Assemble all the parts of the RTF code, set the RTF property of the richtextbox
            RichTextBox1.Rtf = Header & Text & " \par " & vbCrLf & "}"
        End Sub
    #End Region
        Public Class DBRichTextBox
            Inherits RichTextBox
            Sub New()
                'The whole purpose of this
                'inherited richtextbox
                'is for the doublebuffering. thats it.
                Me.DoubleBuffered = True
            End Sub
        End Class
    End Class

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