How to use Memory Mapped Files in vb.net

Account Home | Help | Blog | Contact us | Log Out

Welcome to Kbytes > Articles

How to use Memory Mapped Files in vb.net

Posted By: siteadmin on 16/11/2018 00:53:00

Here is a simple set of functions that will permit you to create, read and overwrite MMF in vb.net

Imports System.IO

Imports System.IO.MemoryMappedFiles

Imports System.Security.AccessControl

Imports System.Security.Principal

Public Class memoryMappedFileManager

Shared Function createMMF(MMFfilename As String, serialisedAppDetails As String) As MemoryMappedFile

Dim mSec = New MemoryMappedFileSecurity

mSec.AddAccessRule(New AccessRule(Of MemoryMappedFileRights)(New SecurityIdentifier(WellKnownSidType.WorldSid, Nothing), MemoryMappedFileRights.FullControl, AccessControlType.Allow))

Dim mmf As MemoryMappedFile = MemoryMappedFile.CreateNew(MMFfilename, 32768, MemoryMappedFileAccess.ReadWrite, MemoryMappedFileOptions.None, mSec, HandleInheritability.Inheritable)

Dim stream As MemoryMappedViewStream = mmf.CreateViewStream()

Dim writer As StreamWriter = New StreamWriter(stream)

writer.Write(serialisedAppDetails)

writer.Flush()

Return mmf

End Function

Shared Function overwriteMMF(MMFfilename As String, serialisedAppDetails As String) As MemoryMappedFile

Dim mmf As MemoryMappedFile = MemoryMappedFile.OpenExisting(MMFfilename)

Dim stream As MemoryMappedViewStream = mmf.CreateViewStream()

'write out remaining space to 32k as vbNull

Dim pad = New String(vbNullChar, 32768 - serialisedAppDetails.Length)

Dim writer As StreamWriter = New StreamWriter(stream)

writer.Write(serialisedAppDetails & pad)

writer.Flush()

' Debug.Print(Text)

Return mmf

End Function

Shared Function readMMF(MMFfilename As String) As String

Dim mmf As MemoryMappedFile = MemoryMappedFile.OpenExisting(MMFfilename, MemoryMappedFileRights.ReadWrite, HandleInheritability.Inheritable)

Dim stream As MemoryMappedViewStream = mmf.CreateViewStream()

'Dim binaryReader = New BinaryReader(stream)

'Dim length = binaryReader.Read() 'gives 11, length of "hello there" string.

'Dim serialisedAppDetails As String = binaryReader.ReadChars(length)

Dim streamReader = New StreamReader(stream)

Dim serialisedAppDetails = streamReader.ReadToEnd()

Return Replace(serialisedAppDetails, vbNullChar, "")

End Function

End Class

Notes:

To use this MemoryMappedFilemanager in your Form (or console) app declare a property that is held in memory as long as the application is running

Public Class Form1

Property mmf As MemoryMappedFile

Sub some_activity()

mmf = memoryMappedFileManager.createMMF("orchMMF", textToWrite)

End Sub

End Class

You can then use the Read and Overwrite MMF methods.

Note the memory mapped file here is limited to 32768 bytes (32K). If you need to allocate more, increase the parameter in the above function.

blog comments powered by Disqus

Kbytes Home | Privacy Policy | Contact us | Testing Area