Question

I wrote a program that does some processing on an image delivered via a web cam. There is an event that fires whenever a new frame is received from the camera. However, this happens more frequently than I’d like – so frequently that my image processing function doesn’t complete before a new event appears and calls the same function again.

How can I control when the event fires? Can I execute my image processing, say, every 5 events instead? I believe I have the pseudo code figured out, but I would prefer to see some examples in C#.

Answer 1

Place the event callback “guarded” as follows. Then it won’t be doing the processing many times at the same time.

private bool m_active;
void YourCallback(object sender, EventArgs args) 
{
  if(!m_active) 
  {
    try 
    { 
      m_active = true;
      // Do the work here... 
    }
    finally { m_active = false; }
  }
}

EDIT : Thread safe if using f.i. Semaphore.

private System.Threading.Semaphore m_Semaphore = new System.Threading.Semaphore(0, 1);
void YourCallback(object sender, EventArgs args) 
{
  if(m_Semaphore.WaitOne(0)) 
  {
    try 
    { 
      // Do the work here... 
    }
    finally { m_Semaphore.Release(); }
  }
}