How to Stop Background Thread that's looping?

How to Stop Background Thread that's looping?

• Dave Salzman

  I have a similar situation...Maybe someone can let me know if this seems reasonable or maybe there is a better way to do this

  I have a little application that communicates with a camera that might need to wait up to 5-10 seconds trying to capture an image because another application might still have the camera open....I don't want to get into that...but anyways...

  I start up a background worker that just keeps banging away at the camera until it either gets the picture, or a certain amount of time elapses.  The way I am handling the timeout is that before I start the background worker, I start a timer on the form/main thread that waits for a predetermined amount of time.

  Once that timespan has elapsed, I do something like this:

  If picWorker.isBusy Then
    picTimer.Stop()
    picWorker.cancelAsync()
  End If

  In my main DoWork loop, I just keep checking to see if the image is nothing and the CancellationPending is false.

  I have a try..except structure in the loop that tries to take a picture. It just swallows the exception if it can't take a picture.  I then just handle the exception of not being able to take the picture once my timeout has fired.

  
  

• tony_qy

  You seem to be on the right track with everything. Here are some suggestions that may solve your problem:

  First, move all the code for starting and stopping the thread to the MeasurementThread class. It is easier to manage the whole thread process if the class is self-contained.
  Second, change the Thread.Join() call to use a timeout value, so it does not block indefinitely.
  Third, add an Abort() method to the class which calls Thread.Abort(), in case setting the flag value does not achieve the desired result.
  Fourth, modify the Thread.Sleep(3000) call to a value far less in order to allow the thread to be more responsive to the change in the execution flag.
  Finally, make sure the variable access is thread-safe - see the lock keyword and the ReaderWriterLock class.

  Here is an example of what I am talking about:

  public class MeasurementThread
  {
  private Thread _Thread;
  private ThreadStart _FunctionPointer;
  private bool _taskRunning;
  private MeasurementThreadCallback _callBackPointer;
  private ReaderWriterLock _Lock;

  ... any other variables here...

  public MeasurementThread(... parameters ...)
  {
  _Lock = new ReaderWriterLock();
  _FunctionPointer = new ThreadStart(Measurement);
  ... any other construction here ...
  }
  
  //Property to tell if the thread is running.
  public bool IsExecuting
  {
  get
  {
  bool returnValue = false; //Return value.

  lock(this)
  {
  _Lock.AcquireReaderLock(10000);
  returnValue = _Thread.IsAlive;
  _Lock.ReleaseLock();
  }
  return returnValue;
  }
  

  }

  //Begins the thread execution.
  public void StartTask()
  {
  MessageBox.Show("MeasurementThread.StartTask");
  _taskRunning = true;

  //Create and launch thread.
  _Thread = new Thread(_FunctionPointer);
  _Thread.IsBackground = true;
  _Thread.Start();
  }
  
  //Ends the thread execution - one way or another
  public void StopTask()
  {
  MessageBox.Show("MeasurementThread.StartTask");
  if (_Thread != null)
  {
  _taskRunning = false;
  _Thread.Join(12000);
  if (_Thread.IsAlive)
  Abort();
  _Thread = null;
  }
  _taskRunning = false;
  }

  //Forces the thread to terminate.
  public void Abort()
  {
  if (_Thread != null)
  {
  _Thread.Abort();
  }
  _Thread = null;
  }

  public void Measurement()
  {
  _taskRunning = true;
  int i = 0;
  while (_taskRunning)
  {
  if (_measureCallback != null)
  {
  Thread.Sleep(500);
  lock(this)
  {
  //If an error occurs in the callback method
  //implementation and is not caught, the thread will
  // be terminated abruptly.
  try
  {
  _measureCallback(i);
  }
  catch (Exception)
  {
  }
  }
  i++;
  }
  }
  }
  }

  --
  Sam Jones
  Adaptive Intelligence
  http://www.adaptiveintelligence.net
  

  
  
  
• How to Stop Background Thread that's looping?