Introduction

Anyone who has used the .NET System.Timers.Timer class for low interval times will realise that it does not offer a very high resolution. The resolution will be system dependant, but a maximum resolution is usually around 15ms (System.Windows.Forms.Timer has an even worse resolution, although it is unlikely a UI will need to be updated this fast). Significantly better performance can be achieved using the Win32 multimedia timer (there are various .NET projects that wrap this timer); however, there are no timers available in the microsecond range.

The problem I encountered was that I needed to send an Ethernet UDP message packet out every 800µs (0.8ms); it did not matter if a packet was slightly delayed or did not go off exactly 800µs after the last one. Basically, what I needed was a microsecond timer that was accurate the majority of the time.

The fundamental problem with a software timer in the region of 1ms is that Windows is a non real-time Operating System (RTOS), and is not suitable for generating regular and accurate events around the 1ms mark. MicroTimer cannot and does not solve this problem; however, it does offer a microsecond timer which offers a reasonable degree of accuracy (approx. 1µs) the majority (approx. 99.9%) of the time. The trouble is, the 0.1% of the time, the timer can be very inaccurate (whilst the Operating System gives some of the processing time to other threads and processes). The accuracy is highly system/processor dependant; a faster system will result in a more accurate timer.

The beauty of MicroTimer is that it is called in a very similar way to the existing System.Timers.Timer class; however, the interval is set in microseconds (as opposed to milliseconds in System.Timers.Timer). On each timed event, MicroTimer invokes the predefined (OnTimedEvent) callback function. The MicroTimerEventArgs properties provide information (to the microsecond) on when exactly (and how late) the timer was invoked.

Using the code

'MicroLibrary.cs' encompasses three classes (under the namespace 'MicroLibrary'):

By design, the amount of work done in the callback function (OnTimedEvent) must be small (e.g., update a variable or fire off a UDP packet). To that end, the work done in the callback function must take significantly less time than the timer interval. Separate threads could be spawned for longer tasks; however, this goes outside the scope of this article. As discussed earlier, because Windows is not a real time Operating System, the callback function (OnTimedEvent) may be late; if this happens and any particular interval is delayed, there are two options:

• Either: Set the property 'IgnoreEventIfLateBy' whereby the callback function (OnTimedEvent) will not be called if the timer is late by the specified number of microseconds. The advantage of this is the timer will not attempt to 'catch up', i.e., it will not call the callback function in quick succession in an attempt to catch up. The disadvantage is that some events will be missed.
• Or: By default, MicroTimer will always try and catch up on the next interval. The advantage of this is the number of times the OnTimeEvent is called will always be correct for the total elapsed time (which is why the OnTimedEvent must take significantly less time than the interval; if it takes a similar or longer time, MicroTimer can never 'catch up' and the timer event will always be late). The disadvantage of this is when it's trying to 'catch up', the actual interval achieved will be much less than the required interval as the callback function is called in quick succession in an attempt to catch up.

The code below shows the 'MicroLibrary' namespace (MicroLibrary.cs) which contains the three classes, MicroStopwatch, MicroTimer, and MicroTimerEventArgs. See the 'Download source' link above.

using System;

namespace MicroLibrary
{
    /// <summary>
    /// MicroStopwatch class
    /// </summary>
    public class MicroStopwatch : System.Diagnostics.Stopwatch
    {
        readonly double _microSecPerTick = 1000000D / Frequency;

        public MicroStopwatch()
        {
            if (!System.Diagnostics.Stopwatch.IsHighResolution)
            {
                throw new Exception("On this system the high-resolution " +
                                    "performance counter is not available");
            }
        }

        public long ElapsedMicroseconds
        {
            get
            {
                return (long)(ElapsedTicks * _microSecPerTick);
            }
        }
    }

    /// <summary>
    /// MicroTimer class
    /// </summary>
    public class MicroTimer
    {
        public delegate void MicroTimerElapsedEventHandler(
                             object sender,
                             MicroTimerEventArgs timerEventArgs);
        public event MicroTimerElapsedEventHandler MicroTimerElapsed;

        System.Threading.Thread _threadTimer = null;
        long _ignoreEventIfLateBy = long.MaxValue;
        long _timerIntervalInMicroSec = 0;
        bool _stopTimer = true;

        public MicroTimer()
        {
        }

        public MicroTimer(long timerIntervalInMicroseconds)
        {
            Interval = timerIntervalInMicroseconds;
        }

        public long Interval
        {
            get { return _timerIntervalInMicroSec; }
            set { _timerIntervalInMicroSec = value; }
        }

        public long IgnoreEventIfLateBy
        {
            get
            {
                return _ignoreEventIfLateBy;
            }
            set
            {
                if (value <= 0)
                    _ignoreEventIfLateBy = long.MaxValue;
                else
                    _ignoreEventIfLateBy = value;
            }
        }

        public bool Enabled
        {
            set
            {
                if (value)
                    Start();
                else
                    Stop();
            }
            get
            {
                return (_threadTimer != null && _threadTimer.IsAlive);
            }
        }

        public void Start()
        {
            if (Enabled || Interval <= 0)
            {
                return;
            }

            _stopTimer = false;
            System.Threading.ThreadStart threadStart = delegate()
            {
                NotificationTimer(Interval, IgnoreEventIfLateBy, ref _stopTimer);
            };
            _threadTimer = new System.Threading.Thread(threadStart);
            _threadTimer.Priority = System.Threading.ThreadPriority.Highest;
            _threadTimer.Start();
        }

        public void Stop()
        {
            _stopTimer = true;

            if (_threadTimer.ManagedThreadId ==
                System.Threading.Thread.CurrentThread.ManagedThreadId)
            {
                return;
            }

            while (Enabled)
            {
                System.Threading.Thread.SpinWait(10);
            }
        }

        void NotificationTimer(long timerInterval,
                               long ignoreEventIfLateBy,
                               ref bool stopTimer)
        {
            int  timerCount = 0;
            long nextNotification = 0;

            MicroStopwatch microStopwatch = new MicroStopwatch();
            microStopwatch.Start();

            while (!stopTimer)
            {
                long callbackFunctionExecutionTime =
                    microStopwatch.ElapsedMicroseconds - nextNotification;
                nextNotification += timerInterval;
                timerCount++;
                long elapsedMicroseconds = 0;

                while ( (elapsedMicroseconds = microStopwatch.ElapsedMicroseconds)
                        < nextNotification)
                {
                    System.Threading.Thread.SpinWait(10);
                }

                long timerLateBy = elapsedMicroseconds - (timerCount * timerInterval);

                if (timerLateBy >= ignoreEventIfLateBy)
                {
                    continue;
                }

                MicroTimerEventArgs microTimerEventArgs =
                     new MicroTimerEventArgs(timerCount,
                                             elapsedMicroseconds,
                                             timerLateBy,
                                             callbackFunctionExecutionTime);
                MicroTimerElapsed(this, microTimerEventArgs);
            }

            microStopwatch.Stop();
        }
    }

    /// <summary>
    /// MicroTimer Event Argument class
    /// </summary>
    public class MicroTimerEventArgs : EventArgs
    {
        // Simple counter, number times timed event (callback function) executed
        public int  TimerCount { get; private set; }

        // Time when timed event was called since timer started
        public long ElapsedMicroseconds { get; private set; }

        // How late the timer was compared to when it should have been called
        public long TimerLateBy { get; private set; }

        // Time it took to execute previous call to callback function (OnTimedEvent)
        public long CallbackFunctionExecutionTime { get; private set; }

        public MicroTimerEventArgs(int  timerCount,
                                   long elapsedMicroseconds,
                                   long timerLateBy,
                                   long callbackFunctionExecutionTime)
        {
            TimerCount = timerCount;
            ElapsedMicroseconds = elapsedMicroseconds;
            TimerLateBy = timerLateBy;
            CallbackFunctionExecutionTime = callbackFunctionExecutionTime;
        }
    }
}

The code below shows a very simple (console application) implementation of the MicroTimer class with the interval set to 1,000µs (1ms). See the 'Download demo project' link above.

using System;

namespace MicroTimerConsoleDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            Program program = new Program();
            program.MicroTimerTest();
        }

        private void MicroTimerTest()
        {
            // Instantiate new MicroTimer and add event handler
            MicroLibrary.MicroTimer microTimer = new MicroLibrary.MicroTimer();
            microTimer.MicroTimerElapsed +=
                new MicroLibrary.MicroTimer.MicroTimerElapsedEventHandler(OnTimedEvent);

            microTimer.Interval = 1000; // Call micro timer every 1000µs (1ms)

            // Can choose to ignore event if late by Xµs (by default will try to catch up)
            // microTimer.IgnoreEventIfLateBy = 500;

            microTimer.Enabled = true; // Start timer

            // Do something whilst events happening, for demo sleep 2000ms (2sec)
            System.Threading.Thread.Sleep(2000);

            microTimer.Enabled = false; // Stop timer

            // Wait for user input
            Console.ReadLine();
        }

        private void OnTimedEvent(object sender,
                                  MicroLibrary.MicroTimerEventArgs timerEventArgs)
        {
            // Do something small that takes significantly less time than Interval
            Console.WriteLine(string.Format(
                "Count = {0:#,0}  Timer = {1:#,0} µs, " + 
                "LateBy = {2:#,0} µs, ExecutionTime = {3:#,0} µs",
                timerEventArgs.TimerCount, timerEventArgs.ElapsedMicroseconds,
                timerEventArgs.TimerLateBy, timerEventArgs.CallbackFunctionExecutionTime));
        }
    }
}

The screenshot below shows the console output. The performance varies on different runs, but was usually accurate to 1µs. Due to system caching, the accuracy was worse on the first run and got better after the first few events. This test was on a 2GHz Dell Inspiron 1545 with an Intel Core 2 Duo (running Windows 7 64bit). The performance improved significantly on faster machines.

Summary

MicroTimer is designed for situations were a very quick timer is required (around the 1ms mark); however, due to the non real-time nature of the Windows Operating System, it can never be accurate. However, as no other microsecond software timers are available, it does offer a reasonable solution for this task (and although processor hungry, is reasonably accurate on fast systems).

History

• 31 July 2010 - Article submitted.