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.

Code:

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

              '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

          Get

              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

              mmf.Dispose()

          Next

          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"

          Try

              '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

              My.Computer.FileSystem.CreateDirectory(Path)

              '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

              DoLayout()

              'randomize the timer

              Randomize()

              '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

                      SB.Append(GetRandomGeneChar)

                  Next

                  '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

                      FS.Close()

                      'Clear the array

                      Array = {}

                      GC.Collect()

                  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)

                  Lines.Add(MemoryMappedFile)

              Next

              '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

              MsgBox(ex.StackTrace)

          End Try

          GC.Collect()

      End Sub

      Private Sub Form1_SizeChanged(sender As Object, e As EventArgs) Handles Me.SizeChanged

          'reposition the controls on the form

          DoLayout()

          'reset the maximum values of the scrollbars because the size of the richtextbox changed

          Try

              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))

          Next

          '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

          Try

              '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