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C# DateTime Performance Class

DateTime performance. A program uses DateTime.Now to frequently capture the time. Can we optimize this? We use a custom class to improve DateTime performance. We cache the DateTime value for Now, improving performance significantly at the cost of accuracy.

Getting current time performance

DateTimeNowCache:  16.5 ns
DateTime.Now:     264.8 ns


Example. Here we see a static utility class in C# that you can use to throttle the number of times the system is queried for the current DateTime. In the class, the constant 20 is used, which means the DateTime is only updated 5% of the time.

ConstStatic Class
C# program that caches DateTime instances

using System;

/// <summary>
/// Utility class to return new DateTimes every few requests.
/// </summary>
public static class DateTimeNowCache
{
    /// <summary>
    /// Refresh time after this many requests.
    /// </summary>
    const int _count = 20;

    /// <summary>
    /// The most recent time collected.
    /// </summary>
    static DateTime _recentTime = DateTime.Now;

    /// <summary>
    /// Number of skipped time collections
    /// </summary>
    static int _skipped;

    /// <summary>
    /// Get the DateTime within the last N calls.
    /// </summary>
    /// <returns>Recent DateTime collected.</returns>
    public static DateTime GetDateTime()
    {
	_skipped++;
	if (_skipped > _count)
	{
	    _recentTime = DateTime.Now;
	    _skipped = 0;
	}
	return _recentTime;
    }
}

The class uses internal accounting to "throttle" the number of times the DateTime is updated. Therefore, using GetDateTime() will be around 20x faster than DateTime.Now, but less "current" 95% of the time.


Benchmark. If we inspect DateTime.Now in IL Disassembler, we see that it internally calls many methods and probably executes hundreds or more lines of code. Eventually, DateTime.Now queries the Windows operating system.

Info: System calls like this are often slow compared to other managed code. We use the above DateTimeNowCache code in a tight loop.

IL Disassembler TutorialIntermediate Language
Notes on benchmark

Iterations: 10000000

Code compared

DateTime now = DateTimeNowCache.GetDateTime();
DateTime now = DateTime.Now;

Benchmark results. Here, the DateTime cache code is about 94% faster. This indicates that the time required for the logic inside the DateTimeNowCache class is minuscule compared to a system query.

Note: Where you would use DateTime.Now as the value you are getting, you can instead use DateTimeNowCache.GetDateTime().


Use. The code here is useful in applications that frequently query the time and service many requests in small amounts of time. For example, if you record traffic on your website, you can use this to improve performance.

Note: The times reported may be a few seconds outdated. Do not use it if the time is critical to your application.


Alternative. An alternative approach is possible. A static DateTime field exists. A static Timer instance updates the DateTime every several seconds. Code that needs the current time simply accesses the static DateTime field.

Timer

Summary. We avoided recalculating the time and repeatedly querying the operating system. In some applications, this can measurably improve performance, as it reduces the number of interop calls to the OS. We cached the DateTimes.