Using lock with Threading.Timer

I have a Windows Service application which uses a Threading.Timer and a TimerCallback to do some processing at particular intervals. I need to lock down this processing code to only 1 thread at a time.

So for example, the service is started and the first callback is triggered and a thread is started and begins processing. This works ok as long as the processing is completed before the next callback. So say for instance the processing is taking a little longer than usual and the TimerCallback is triggered again whilst another thread is processing, I need to make that thread wait until the other thread is done.

Here's a sample of my code:

static Timer timer;
static object locker = new object();

public void Start()
{
    var callback = new TimerCallback(DoSomething);
    timer = new Timer(callback, null, 0, 10000);
}

public void DoSomething()
{
      lock(locker)
      {
           // my processing code
      }
}

Is this a safe way of doing this? What happens if the queue gets quite substantial? Is there a better option?

c# multithreading locking

Edit Report

The worst that can happen if the processing code takes more than 10s to execute is that you will be wasting 1 threadpool thread every time there's a new callback called (they will be waiting for in the lock statement). And if you take all the threadpool threads HttpWebRequest, ASP.NET, asynchronous delegate invocations... will suffer.

What I would do is to schedule the first callback immediately. Then, if you really need your DoSomething() to be called every 10s:

public void DoSomething ()
{
       DateTime start = DateTime.UtcNow;
       ...
       TimeSpan elapsed = (DateTime.UtcNow - start);
       int due_in = (int) (10000 - elapsed.TotalMilliseconds);
       if (due_in < 0)
           due_in = 0;
       timer.Change (due_in, Timeout.Infinite);
}

Or something along that line.

answered 2009-11-08T23:58:08.613

Using lock with Threading.Timer

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