UIJobScheduler.cs

namespace Scheduler
{
    using System;
    using System.Windows.Forms;
    using System.Diagnostics;
    using System.Collections.Generic;

    public static class UIJobScheduler
    {
        static readonly List<Job> jobs = new List<Job>();
        static readonly Timer timer = new Timer();

        class Job
        {
            readonly Action<object> action;
            readonly object state;
            readonly int interval;
            DateTime nextRunDate;

            public Job(int millisecondsInterval, Action<object> action, object state)
            {
                this.action = action;
                this.state = state;
                this.nextRunDate = TruncatedUtcNow();
                interval = millisecondsInterval;
            }

            public void CheckExecute(ref DateTime utcNow)
            {
                Debug.WriteLine("[CheckExecute] Now: " + utcNow.ToString("mm:ss.fff") + " nextRunDate: " + nextRunDate.ToString("mm:ss.fff") + " interval: " + interval);
                if(nextRunDate > utcNow)
                {
                    return;
                }
                nextRunDate = utcNow.AddMilliseconds(interval);
                try
                {
                    action(state);
                }
                catch(Exception ex)
                {
                    Trace.WriteLine(ex);
                }
            }
        }

        static UIJobScheduler()
        {
            timer.Tick += new EventHandler(TimerFunction);
            timer.Start();
        }

        static void TimerFunction(object sender, EventArgs e)
        {
            DateTime utcNow = TruncatedUtcNow();
            foreach(Job job in jobs)
            {
                job.CheckExecute(ref utcNow);
            }
        }

        public static void Register(int millisecondsInterval, Action<object> action)
        {
            Register(millisecondsInterval, action, null);
        }

        public static void Register(int millisecondsInterval, Action<object> action, object state)
        {
            if(millisecondsInterval <= 0)
            {
                throw new ArgumentOutOfRangeException("millisecondsInterval");
            }
            if(action == null)
            {
                throw new ArgumentNullException("action");
            }
            Job job = new Job(millisecondsInterval, action, state);
            jobs.Add(job);
            timer.Interval = Gcd(millisecondsInterval, timer.Interval);
        }

        static DateTime TruncatedUtcNow()
        {
            DateTime utcNow = DateTime.UtcNow;
            return new DateTime(utcNow.Year, utcNow.Month, utcNow.Day, utcNow.Hour, utcNow.Minute, utcNow.Second, utcNow.Millisecond);
        }

        static int Gcd(int a, int b)
        {
            while(b != 0)
            {
                int oldA = a;
                a = b;
                b = oldA % b;
            }
            return a;
        }
    }
}