CODEWITHSUNDEEP
c#timer
Andrew Simpson
Andrew Simpson

Reputation: 7324

System.Threading callback does not seem that accurate

My application receives instructions from my client.

On each instruction I want to execute code from the received timestamp + 10 seconds.

To test the accuracy of my code I mocked up this simple console test:

    static DateTime d1 = DateTime.Now;
    static Timer _timer = null;
    static void Main(string[] args)
    {
        _timer = new Timer(Callback, null,200, Timeout.Infinite);
       d1 = DateTime.Now;
       Console.ReadLine();
    }

    private static void Callback(Object state)
    {
        TimeSpan s = DateTime.Now - d1;
        Console.WriteLine("Done, took {0} secs.", s.Milliseconds);
        _timer.Change(200, Timeout.Infinite);
    }

On running it I had hoped to display:

Done, took 200 milsecs.
Done, took 200 milsecs.
Done, took 200 milsecs.
Done, took 200 milsecs.
Done, took 200 milsecs.
Done, took 200 milsecs.

But it does not.

I get random values for 'milsecs'.

NB My actual code will not always be using 200 milliseconds.

Example Screenshot:

enter image description here

Upvotes: 1

Views: 49

Answers (2)

David
David

Reputation: 10708

First, you're using the TimeSpan.Milliseconds property, which is an int and only returns the Millisecond part of the timespan. To make sure you're getting the full time, use TotalMilliseconds

Second, you're not resetting d1 with each loop, so you'll see the total time, not the time per iteration. To fix this, make sure to set d1 = DateTime.Now at the end of your callback so the next loop is using the right time.

Finally, you may see a certain discrepancy rather than perfect 200ms intervals, due to the overhead of threading, method calls, and even the subtraction operation you're doing. In addition, DateTime does not always have the greatest accuracy - according to this article from Eric Lippert:

If the question you want to ask is about how long some operation took, and you want a high-precision, high-accuracy answer, then use the StopWatch class.

Thus:

static Stopwatch _watch = Stopwatch.StartNew();
static Timer _timer = null;
static void Main(string[] args)
{
    _timer = new Timer(Callback, null,200, Timeout.Infinite);
   Console.ReadLine();
}

private static void Callback(Object state)
{
    TimeSpan s = _watch.Elapsed;
    _watch.Restart();
    Console.WriteLine("Done, took {0} secs.", s.TotalMilliseconds);
    _timer.Change(200, Timeout.Infinite);
}

Upvotes: 3

usr
usr

Reputation: 171178

s.Milliseconds is the milliseonds after the decimal point so to speak. You need TotalMilliseconds. Those properties are horribly named. They are the cause for many SO questions.

The built-in timers should have about 15ms resolution (or a small multiple of it) and potentially some skew (I don't know).

Upvotes: 1

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