如何在繁忙的ASP.NET MVC中定义全局变量

Question

In my site, I call a third party API. To avoid hitting its rate limit, I need to define a global variable to enqueue requests. ( I'm using RateLimiter any better solution?)

namespace MySite.App_Start
{
    public static class Global
    {
        public static int MaxCount { get; set; } = 30;
        public static TimeSpan Interval { get; set; } = TimeSpan.FromSeconds(1);

        private static TimeLimiter rateLimiter;
        public static TimeLimiter RateLimiter
        {
            get
            {
                if (rateLimiter == null)
                    rateLimiter = TimeLimiter.GetFromMaxCountByInterval(MaxCount, Interval);

                return rateLimiter;
            }
        }
    }
}

Then I'll use RateLimiter property. But I've read a lot that having a global variable is not a good idea. Considering my site has a lot of requests per second, is my code safe to use? Thanks.

Answer 1

Your code isn't 100% safe since it could create multiple instances of TimeLimiter in the beginning and depending on surrounding code, it could be a problem. I'm guessing it wouldn't be a big problem, but it's better to write the code properly to begin with.

This is something an IoC container handles nicely, but if you don't want to use one, you could use Lazy:

private static TimeLimiter rateLimiter = new Lazy(() =>
    TimeLimiter.GetFromMaxCountByInterval(MaxCount, Interval));
public static TimeLimiter RateLimiter => rateLimiter.Value;

Answer 2

Maybe, you can make it thread-safe by using lock statement.

public static class Global
{
    public static int MaxCount { get; set; } = 30;
    public static TimeSpan Interval { get; set; } = TimeSpan.FromSeconds(1);

    private static object _lockObject = new object();
    private static TimeLimiter rateLimiter;
    public static TimeLimiter RateLimiter
    {
        get
        {
            lock (_lockObject)
            {
                if (rateLimiter == null)
                    rateLimiter = TimeLimiter.GetFromMaxCountByInterval(MaxCount, Interval);
                return rateLimiter;
            }

        }
    }
}

Answer 3

Your code is not thread-safety. Try this:

public class Singleton
{      
  protected Singleton() { }
  private sealed class SingletonCreator
  {
    private static readonly Singleton instance = new Singleton();
    public static Singleton Instance { get { return instance; } }
  }
  public static Singleton Instance
  {
    get { return SingletonCreator.Instance; }
  }
}

Or use your favorite IoC-container with creating SingleInstance object