#1) Threading
#2) Registry Access
Back in my VB6 days my team tried many times to get things to work muti-threaded, there were magazine articles at the time that claimed to be able to do it using windows API hacks, and MDI forms, but we were never able to get it to work. In .NET you just have to call .Start on a thread object is just Amazing.
Registry access in VB6 was crazy. You had to write pages and pages of code using a bunch of Win32 API Calls. In .NET I changed my pages of code into just a few lines. Once I wrote my first .NET Registry access routine I never wanted to write in VB6 again.
Here is some code that I modified that does both Registry Access and threading. I'm not sure who wrote this code originally, but I modified it so it would be thread safe. Your form needs to have the following controls:
A timer named Timer1, set to go off every 5 seconds (5000 ms)
A datagrid control named DataGridView1
Two buttons Button1 and Button2
If your are using this on a VISTA box you will need to set your UAC Settings, see this post for more information. http://vb-daryl.blogspot.com/2009/11/uac-administrator-access.html
Imports System.Threading.Thread
Imports Microsoft.Win32
Public Class Form1
Dim dtResults As DataTable
Dim dtFound As DataTable
Public Shared ProcessThread As System.Threading.Thread
Dim Path As String = "SYSTEM\\"
Dim SearchStr As String = "USERNAME"
Dim WaitRequest As Boolean
Dim TS As ThreadStatus
Enum ThreadStatus
Running
Wating
End Enum
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
dtResults = New DataTable
dtResults.Columns.Add("Name", GetType(String))
dtResults.Columns.Add("Value", GetType(String))
dtFound = New DataTable
dtFound.Columns.Add("Name", GetType(String))
dtFound.Columns.Add("Value", GetType(String))
Timer1.Enabled = True
TS = ThreadStatus.Running
ProcessThread = New System.Threading.Thread(AddressOf SearchThread)
ProcessThread.Start()
' SearchThread()
End Sub
Sub SearchThread()
Search(Path, SearchStr)
MsgBox("Search Complete")
End Sub
Public Sub Search(ByVal Path As String, ByVal SearchStr As String)
If WaitRequest = True Then
WaitRequest = False
TS = ThreadStatus.Wating
While TS = ThreadStatus.Wating
System.Threading.Thread.Sleep(10)
End While
End If
Dim dRow As DataRow
Dim ParentKey As RegistryKey = Registry.LocalMachine.OpenSubKey(Path, True)
' Loop through values in the subkey
For Each valueName As String In ParentKey.GetValueNames()
On Error Resume Next
'Create String to Compare against
Dim CurStr As String = valueName + " = " + ParentKey.GetValue(valueName)
Dim CurValue As String = ParentKey.GetValue(valueName)
dRow = dtResults.NewRow
dRow("Name") = valueName
dRow("Value") = ParentKey.GetValue(valueName)
dtResults.Rows.Add(dRow)
'ListBox1.Items.Insert(0, valueName + " = " + ParentKey.GetValue(valueName))
If CurValue = SearchStr Then
Dim dRowF As DataRow = dtFound.NewRow()
dRowF("Name") = valueName
dRowF("Value") = CurValue
dtFound.Rows.Add(dRowF)
CurStr = ""
CurValue = ""
End If
Next
'if there are sub keys loop through and be recursive
If ParentKey.SubKeyCount > 0 Then
For Each subKeyName As String In ParentKey.GetSubKeyNames()
dRow = dtResults.NewRow
dRow("Name") = Path + subKeyName
dRow("Value") = ""
dtResults.Rows.Add(dRow)
'ListBox1.Items.Insert(0, "")
'ListBox1.Items.Insert(0, Path + subKeyName) ' Writing the Keyname
'This is what makes me recursive!
Dim Thispath As String = Path + subKeyName + "\\"
Search(Thispath, SearchStr)
Next
End If
End Sub
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
WaitRequest = True
Timer1.Stop()
While TS = ThreadStatus.Running
System.Threading.Thread.Sleep(10)
Application.DoEvents()
End While
Me.Label1.Text = "Checked " & dtResults.Rows.Count & " Rows"
Dim dtTemp As DataTable = dtResults.Copy
Dim dtTempF As DataTable = dtFound.Copy
Me.DataGridView1.DataSource = dtTemp
Me.DataGridView2.DataSource = dtTempF
TS = ThreadStatus.Running
Timer1.Start()
Dim x As DataView = New DataView(dtTemp)
x.Sort = "idOrder, Name"
End Sub
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
ProcessThread.Abort()
ProcessThread = Nothing
End Sub
End Class
This code does have a bug that I didn't take the time to figure out, after it searches 200,000 or so keys it starts crashing. I'm not sure why, my guess is it is trying to access some System Protected Key, but this code works well enough that I am not going to worry about that.
Now that you've seen that I would like to discuss some of the concepts that you need to be aware of in Threading.
Mainly "Thread Safety" and "Thread Management".
"Thread Safety"
Most people new to threading do not think much about this, you spawn some thread and want to post it's results back to the UI. But you will find when you code tries to access a datagrid, or listbox that is on the UI thread that it will throw an error as a background thread will not be allowed to mess with the UI thread. There are a number of solutions to this, I generally use the Singleton pattern to create a buffer to hold data in. I'll talk more about Singletons in later posts. For this example I decided to use the timer control to pause the background thread, and update the UI with it's current results.
"Thread Management"
This concept is important as well. If you do not stop your other threads when your application is shut down they will keep running forever. You also need to be concerned about how many threads you create. The first time I wrote a threading application I wrote a program which searched all files and folders on a hard drive. The main thread searched for new folders, and it spawned another thread to search the files. As it ran it just kept spawning thread after thread until it hit around 32,000 threads at which time my computer, without giving an error message, turned itself off. In this example we only create one thread so you need not worry about it crashing you computer.
I generally create my own threading class which spawns a set number of threads (usually in it's constructor) and manages them. It keeps a Queue of new things to spawn threads for, and then checks the status of each thread, once the thread is done with it's task the threading class records the results, disposes the thread and creates a new thread with the next task in it's Queue. I believe this is called "Thread Polling" but I don't know I created this method on my own without reading about it.
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