Problem with threading in C#

Problem with threading in C#

• Umeshnath

  There are another couple of problems:
  
  When the button is clicked to stop the thread, then the while loop in StartThread() exits, and the thread terminates.
  
  It looks like you're using bStartThread to control the non-UI thread, with the intention that it continues running. If so, you should enclose the code in StartThread in an infinite loop:
  
  while( true )
  {
      while( this.bStartThread )
      {
         Thread.Sleep(500);
         // invoke a delegate on the form to update dataSet.
      }
  }
  
  and only Start the thread if its IsAlive property is false.
  
  Otherwise, if your intention is to allow the thread to stop when clicking the button, then you've got more work to do:
  
  You should Join() the thread after setting bStartThread to false, otherwise the user could click the button (if they're a fast clicker!) to start the thread again before it had finished terminating and you'd be attempting to Start a thread that is still in the started state.
  
  You can't Start a terminated thread, so you'd have to go ahead and create a new thread instance each time.
  
  
  
  
  
  
  
  

• Juice Johnson

  Hi,Daniel,
  Thank you for the advise and this helpful links.
  This was very usefil to me to fix the problem.
  
  :-)
  
  

• AJMurray

  Here's some code that does the two cases I described:
  
          [STAThread]
          static void Main()
          {
              Application.Run(new Form1());
          }
  
          public delegate void AddRowDelegate();
  
          private void AddRow()
          {
              DataRow dr = this.dataSet1.Tables["Table1"].NewRow();
              this.dataSet1.Tables["Table1"].Rows.Add( dr );
              dr.BeginEdit();
              dr["Column2"] = "test "+dr["Column1"].ToString();
              dr.AcceptChanges();
              dr.EndEdit();
          }
  
          // Code below for creating a new thread each time
  
          private void button1_Click(object sender, System.EventArgs e)
          {
              if (! this.bStartThread )
              {
                  this.bStartThread = true;
                  this.button1.Text = "Stop Thread";
                  this.thread = new System.Threading.Thread( new ThreadStart(StartThread) );
                  this.thread.Name = "Test";
                  this.thread.IsBackground = true;
                  this.thread.Start();
              }
              else
              {
                  this.bStartThread = false;
                  this.button1.Text = "Start Thread";
                  while (this.thread.ThreadState == ThreadState.Running || this.thread.ThreadState == ThreadState.WaitSleepJoin)
                  {
                      Thread.Sleep(200);
                  }
                  this.thread.Join();
              }
          }
  
          private void StartThread()
          {
              while ( this.bStartThread )
              {
                  Thread.Sleep(500);
                  Console.WriteLine("About to invoke");
                  // BeginInvoke - don't want to block waiting for UI thread to update,
                  // as it's going to be busy waiting for this work to be completed.
                  this.BeginInvoke( new AddRowDelegate( AddRow ) );
                  Console.WriteLine("invoked");
              }
          }
  
          // Code below for keeping thread alive.
  
  //        private void button1_Click(object sender, System.EventArgs e)
  //        {
  //            if (! this.bStartThread )
  //            {
  //                this.bStartThread = true;
  //                this.button1.Text = "Stop Thread";
  //                if ( !this.thread.IsAlive )
  //                {
  //                    this.thread.Start();
  //                }
  //            }
  //            else
  //            {
  //                this.bStartThread = false;
  //                this.button1.Text = "Start Thread";
  //            }
  //        }
  //
  //        private void StartThread()
  //        {
  //            while(true)
  //            {
  //                while ( this.bStartThread )
  //                {
  //                    this.Invoke( new AddRowDelegate( AddRow ) );
  //                    Thread.Sleep(500);
  //                }
  //            }
  //        }
      }
  
  
  

• Deepak K

  The problem is in your StartThread method. Since it runs on a different thread, you're not allowed to access the Form's controls. You need to use Invoke to perform the changes you want to do on the original thread.
  
  Here are some articles on Invoke:
  http://www.theserverside.net/discussions/thread.tss thread_id=25063 (with code sample)
  http://weblogs.asp.net/justin_rogers/articles/126345.aspx (advanced)
  
  
• Problem with threading in C#