public class RecurringJob : IJob, IRegisteredObject
{
    private static readonly object currentLock = new object();
    private static bool active = false;

    private static bool CanContinue {
        get {
            lock(currentLock){
                return !active;
            }
        }
    }

    public RecurringJob()
    {
        //code to setup job
    }

    public void Execute()
    {
        if (CanContinue)
        {
            active = true;
            //do work here
            active = false;
        }
    }

    public void Stop(bool immediate)
    {
        //code to handle application stopping graefully
    }
}