Threads how many and how to stop?

Using System.Threading

I want to be able to start threads arbitrarily by my application. When I do, how can I tell how many threads are running?

Also, how can I kill a thread?

Finally, how does a thread kill itself?

VB Code:

Imports System.Threading
 
Public Class Form1
    Inherits System.Windows.Forms.Form
    Dim LFile As String
    Dim LFileSize As Int32 = 32767
    Dim LineArray() As String
    Dim NameArray() As String
 
    Public nThreads As Int16 = 0
 
#Region " Windows Form Designer generated code "
 
    Public Sub New()
        MyBase.New()
 
        'This call is required by the Windows Form Designer.
        InitializeComponent()
 
        'Add any initialization after the InitializeComponent() call
 
    End Sub
 
    'Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub
 
    'Required by the Windows Form Designer
    Private components As System.ComponentModel.IContainer
 
    'NOTE: The following procedure is required by the Windows Form Designer
    'It can be modified using the Windows Form Designer.  
    'Do not modify it using the code editor.
    Friend WithEvents eLabel As System.Windows.Forms.Label
    Friend WithEvents Timer1 As System.Windows.Forms.Timer
    Friend WithEvents txtIP As System.Windows.Forms.TextBox
    Friend WithEvents cmbLocale As System.Windows.Forms.ComboBox
    Friend WithEvents Label1 As System.Windows.Forms.Label
    Friend WithEvents Label2 As System.Windows.Forms.Label
    Friend WithEvents Button1 As System.Windows.Forms.Button
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.components = New System.ComponentModel.Container()
        Me.eLabel = New System.Windows.Forms.Label()
        Me.Timer1 = New System.Windows.Forms.Timer(Me.components)
        Me.txtIP = New System.Windows.Forms.TextBox()
        Me.cmbLocale = New System.Windows.Forms.ComboBox()
        Me.Label1 = New System.Windows.Forms.Label()
        Me.Label2 = New System.Windows.Forms.Label()
        Me.Button1 = New System.Windows.Forms.Button()
        Me.SuspendLayout()
        '
        'eLabel
        '
        Me.eLabel.Location = New System.Drawing.Point(0, 64)
        Me.eLabel.Name = "eLabel"
        Me.eLabel.Size = New System.Drawing.Size(336, 168)
        Me.eLabel.TabIndex = 0
        '
        'Timer1
        '
        Me.Timer1.Interval = 500
        '
        'txtIP
        '
        Me.txtIP.Location = New System.Drawing.Point(96, 8)
        Me.txtIP.Name = "txtIP"
        Me.txtIP.Size = New System.Drawing.Size(120, 20)
        Me.txtIP.TabIndex = 1
        '
        'cmbLocale
        '
        Me.cmbLocale.Location = New System.Drawing.Point(96, 32)
        Me.cmbLocale.Name = "cmbLocale"
        Me.cmbLocale.Size = New System.Drawing.Size(232, 21)
        Me.cmbLocale.TabIndex = 2
        '
        'Label1
        '
        Me.Label1.Location = New System.Drawing.Point(8, 8)
        Me.Label1.Name = "Label1"
        Me.Label1.Size = New System.Drawing.Size(80, 23)
        Me.Label1.TabIndex = 3
        Me.Label1.Text = "IP Address"
        '
        'Label2
        '
        Me.Label2.Location = New System.Drawing.Point(8, 32)
        Me.Label2.Name = "Label2"
        Me.Label2.Size = New System.Drawing.Size(80, 16)
        Me.Label2.TabIndex = 4
        Me.Label2.Text = "Temp Locale"
        '
        'Button1
        '
        Me.Button1.Location = New System.Drawing.Point(224, 8)
        Me.Button1.Name = "Button1"
        Me.Button1.Size = New System.Drawing.Size(104, 24)
        Me.Button1.TabIndex = 5
        Me.Button1.Text = "Start | Stop"
        '
        'Form1
        '
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(336, 230)
        Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.Button1, Me.Label2, Me.Label1, Me.cmbLocale, Me.txtIP, Me.eLabel})
        Me.Name = "Form1"
        Me.Text = "Downloader"
        Me.ResumeLayout(False)
 
    End Sub
 
#End Region
    Public Declare Function DeleteUrlCacheEntry Lib "Wininet.dll" _
       Alias "DeleteUrlCacheEntryA" _
      (ByVal lpszUrlName As String) As Long
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim theNet As New System.Net.WebClient()
        Dim theDataBuffer As Byte()
        Dim DLFile As String
        Dim x As Int16
 
        For x = 0 To 25
            cmbLocale.Items.Add(Chr(x + 65) & ":\")
        Next
        theDataBuffer = theNet.DownloadData("http://" & txtIP.Text)
        DLFile = System.Text.Encoding.ASCII.GetString(theDataBuffer)
        LineArray = Split(DLFile, (Chr(10)))
        NameArray = Split(DLFile, (Chr(10)))
        For x = 0 To UBound(LineArray)
            If (Len(Mid(LineArray(x), InStrRev(LineArray(x), "<td>") + 4)) < (Len(LineArray(x)) - 5)) AndAlso (InStrRev(NameArray(x), "</a>") > 0) Then
                LineArray(x) = Mid(LineArray(x), InStrRev(LineArray(x), "<td>") + 4)
                NameArray(x) = Mid(NameArray(x), InStrRev(NameArray(x), """>") + 2)
                NameArray(x) = Mid(NameArray(x), 1, InStrRev(NameArray(x), "</a>") - 1)
                If (LFileSize > Val(LineArray(x))) AndAlso (Val(LineArray(x)) > 1000) Then
                    LFileSize = LineArray(x)
                    LFile = NameArray(x)
                End If
            Else
                LineArray(x) = ""
                NameArray(x) = ""
            End If
        Next
    End Sub
 
    Private Sub Form1_Unload(ByVal sender As System.Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles MyBase.Closing
 
    End Sub
 
    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        Try
            Dim dlthd As DLThread = New DLThread(eLabel, cmbLocale, NameArray, txtIP)
            Dim thd As Thread = New Thread(AddressOf dlthd.DoWork)
            thd.Priority = ThreadPriority.BelowNormal
            thd.Start()
        Catch
        End Try
    End Sub
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Timer1.Enabled = Not Timer1.Enabled
    End Sub
End Class
 
Public Class DLThread
    Public Declare Function DeleteUrlCacheEntry Lib "Wininet.dll" _
       Alias "DeleteUrlCacheEntryA" _
      (ByVal lpszUrlName As String) As Long
 
    Private ginLabel As Label
    Private gcmbLocale As ComboBox
    Private gNameArray As System.Array
    Private gtxtIP As TextBox
 
    Public Sub New(ByRef inLabel As Label, ByVal cmbLocale As ComboBox, ByVal NameArray As System.Array, ByVal txtIP As TextBox)
        ginLabel = inLabel
        gcmbLocale = cmbLocale
        gNameArray = NameArray
        gtxtIP = txtIP
    End Sub
 
    Public Sub DoWork()
 
        Try
            ginLabel.Text = ""
            Randomize()
            Dim theNet As New System.Net.WebClient()
            Dim theFile As String = gcmbLocale.SelectedItem & "file." & Rnd() * 32767
            Dim DLEntry As String = "http://" & gtxtIP.Text & "/" & gNameArray(Int(Rnd() * UBound(gNameArray)))
            DeleteUrlCacheEntry(DLEntry)
 
                        theNet.DownloadFile(DLEntry, theFile)
            Kill(theFile)
        Catch ee As System.Net.WebException
            ginLabel.Text = ee.ToString()
        End Try
    End Sub
End Class

You can use Abort method to stop a thread.

You can check whether its running or not with the ThreadState property.

The easiest way to track them would to make a collection or array of the threads you've started until then end.

threads kill themselves when they've finished running unless they're in an infinite loop or something.

To call the abort function for a thread you'll need to have a permanent reference to your thread (easiest way is to keep the threads in a collection)

You could create your own class that does thread management. It could have methods like Add, Abort, Count to get the state of your threads, as well as a function that runs every 3 seconds (or so) to get the status of the threads and update the count property.

i think by using a (shared) collection to keep track of threads in effect you ARE creating a thread management class since you are adding and aborting threads.

Anyway, just a suggestion to reduce your future headache when dealing with threads.

Make good use of locks for your shared resources.

The counter for the number of threads running is a good candidate. So is the collection of threads itself.

Quote:

The counter for the number of threads running is a good candidate. So is the collection of threads itself.

The counter will propably by of type int (32 bit), on a 32 bit OS it's not necessary to lock/sync the counter (of type int) because changing the value will be done within 1 CPU cycle.

Looking at all the suggestions you'd probably want to take a look at using the CLR threadpool, and not managing threads yourself (if possible ofcourse) or building your own threadpool.

An easy and good way is using async delegates, which make use of the CLR threadpool.