Can I Store whole Files in Memory (RAM Disk or Cache)?

Question

I am writing an application which needs very fast file access - reading from disk can be "slow" depending on the disk type. A RAM disk would be ideal for temporary storage but I have not found any way to set one up. Can someone point me in a direction where I can learn how to do this (or even show me). Failing that, can a memory cache be used in a similar way to temporarily store whole files? If so, how?

All the best,
Jim.

Answer 1

With Memory Mapped files : MemoryMappedFile Class

Answer 2

I'm tempted to try the RAM disk route if there are any suggestions.

Some sources with which to experiment:

List of RAM drive software
https://en.wikipedia.org/wiki/List_of_RAM_drive_software

The last Windows suggestion might be worth trying first:

"Native
Windows also has a rough analog to tmpfs in the form of
"temporary files". Files created with both
FILE_ATTRIBUTE_TEMPORARY and FILE_FLAG_DELETE_ON_CLOSE
are held in memory and only written to disk if the system
experiences high memory pressure."

Also check out:

"ImDisk Virtual Disk Driver is a disk image emulator created
by Olof Lagerkvist. It is free and open-source software, and
is available in 32- and 64-bit variants. "

See the overview of this utility here:

How to Set up and Use a Ram Drive in Windows 10
https://www.maketecheasier.com/setup-ram-disk-windows/

• Wayne

Answer 3

I would create an object that had a path to the mht file and a string for the document text. As part of the decompression process I'd create objects for each of the files and store them in a dictionary based on page name.

When browsing I'd check to see if the document text was empty. If not just set the webrowser's document text from that, if it was empty I'd navigate to the path and when the navigation was complete I'd set the document text in the object.

This way it is only slow the first time a page is accessed.

Answer 4

This shows what I mentioned earlier,

Public Class Form1

    Private myMHT As MHTFiles
    Private initedMHT As Boolean = False
    Private currentItem As MHTFiles.MHTf

    Private Sub Form1_Shown(sender As Object, e As EventArgs) Handles Me.Shown
        'p has foler with mht / mhtml files
        Dim p As String = Environment.GetFolderPath(Environment.SpecialFolder.Desktop)
        p = IO.Path.Combine(p, "MHT")
        My.Settings.MHTPath = p

        myMHT = New MHTFiles(p)

        ComboBox1.DataSource = myMHT.Names
        ComboBox1.SelectedIndex = -1
        initedMHT = True
    End Sub

    Private Sub Form1_FormClosing(sender As Object, e As FormClosingEventArgs) Handles Me.FormClosing
        Try
            ' IO.Directory.Delete(My.Settings.MHTPath, True)
        Catch ex As Exception

        End Try
    End Sub

    Private Sub ComboBox1_SelectedIndexChanged(sender As Object,
                                               e As EventArgs) Handles ComboBox1.SelectedIndexChanged
        If Not initedMHT Then Exit Sub
        'get an item
        currentItem = myMHT.Item(ComboBox1.SelectedItem.ToString)
        If currentItem IsNot Nothing Then
            naviLock.WaitOne() 'browser wait lock
            If currentItem.Navigate Then
                'first time navigate, see WebBrowser1_DocumentCompleted
                WebBrowser1.Navigate(currentItem.path)
            Else
                'was previously navigated
                WebBrowser1.DocumentText = currentItem.docText
                naviLock.Set()
            End If
        End If
    End Sub

    Private naviLock As New Threading.AutoResetEvent(True)
    Private Sub WebBrowser1_DocumentCompleted(sender As Object, e As WebBrowserDocumentCompletedEventArgs) Handles WebBrowser1.DocumentCompleted
        If currentItem.Navigate Then
            currentItem.docText = WebBrowser1.DocumentText
        End If
        naviLock.Set() 'set the lock
    End Sub
End Class

Public Class MHTFiles
    Private Dict As New Dictionary(Of String, MHTf)

    Public Sub New(DirWithMHTfiles As String)

        Dim fs() As String = IO.Directory.GetFiles(DirWithMHTfiles)
        Dim mht As IEnumerable(Of String)
        mht = From fn In fs
                Let ext = IO.Path.GetExtension(fn).ToLower.TrimStart("."c)
                Where ext = "mhtml" OrElse
                        ext = "mht"
                Select fn

        For Each f As String In mht
            Dim d As New MHTf
            d.path = f
            Me.Dict.Add(IO.Path.GetFileNameWithoutExtension(f), d)
        Next
    End Sub

    Public Function Item(ItemName As String) As MHTf
        Dim rv As MHTf
        If Me.Dict.ContainsKey(ItemName) Then
            rv = Me.Dict(ItemName)
        End If
        Return rv
    End Function

    Public Function Names() As List(Of String)
        Return Me.Dict.Keys.ToList
    End Function

    Public Class MHTf
        Public Function Navigate() As Boolean
            Return Me.docText = ""
        End Function

        Public path As String
        Public docText As String = ""
    End Class
End Class