Use of cache in C ＃

brief introduction

Cache refers to the memory that can exchange high-speed data , It precedes memory and CPU Exchange data , So the speed is very fast . because CPU Reading data from memory is several orders of magnitude faster than reading data from disk , And it's in memory , Reduce the pressure of database access , So caching is used in almost every project . Commonly used are MemoryCache、Redis Today I will bring you MemoryCache Introduction to the use of ！

Category

Memory cache expiration time is 4 Kind of

• Never expire • Absolute expiration time • Relative to the current expiration time • Slide expiration time

Of course, it can also be derived from these three expiration times The sliding window + Absolute expiration time, etc

Official website address

We can also check the official documents To learn more about MemoryCache I won't read too much here

•MemoryCache Address

Use

Go back to the question Let's introduce how to set the expiration time !

Never expire

After my program is released, as long as we don't clean up the cache , The cache will remain valid ！

 /// <summary>
 ///  Never expire 
 /// </summary>
static void NeverExpire()
{
       _cache.Set("NeverExpire", "1");
}

Absolute expiration time

In absolute time Can be interpreted as " Closing date "

static void AbsoluteExpiration()
 {
  DateTime time = new DateTime(2022, 04, 01, 23, 59, 59);
   _cache.Set("AbsoluteExpiration", "20220401235959", time);
}

Relative to the current expiration time

Relative to the current expiration time , For example, it is valid within one minute after we set the cache , You can refer to our common SMS login , The back-end randomly generates a verification code and stores it in redis, And set the key The expiration time of , And then there's verification , Send mobile phone number and verification code to the background , from redis Take out the corresponding verification code and check it , If correct, delete the captcha , Prevent multiple verifications

 static void ExpirationTimeRelativeToThePresent()
    {
          _cache.Set("AbsoluteExpiration", "123456", new TimeSpan(0, 0, 60));
   }

Slide expiration time

The cache is not used within the set time , Failure , After use, the expiration time of the cache is refreshed again

 static void SlidingExpirationTime()
 {
       _cache.Set("SlidingExpirationTime", "3", new MemoryCacheEntryOptions()
       {
              SlidingExpiration = new TimeSpan(0, 0, 2),
                AbsoluteExpiration = DateTimeOffset.Now.AddMilliseconds(1000)
       });
 }

Let's take a look at the definition of the official website, as shown in the figure !

Then explain the second parameter MemoryCacheEntryOptions, Set the absolute expiration date of the cache item : Is after the current cache setting 1000 minute . Like the hero League mobile game we often play , We don't log in for a day , The cache token invalid , You have to log in again to get token, Every day we're out of time to play , You don't need to start every time app Login account at , however After playing for a while , It is found that we still need to log in to our account again. This is the absolute expiration time in the sliding expiration time ！

Get cache value

ConcurrentDictionary<object, CacheEntry> _entries： A multi thread safe dictionary type , In fact, the essence of cache is this dictionary , Put all caches into this dictionary , Then through the dictionary key( Dictionary key In fact, it is similar to caching entities CacheEntry Of key Have the same value ) obtain CacheEntry Entity (CacheEntry Entity contains key and value, That's what we set in our code key and value).

 static void GetCache()
 {
  // Mode one 
  _cache.Get("NeverExpire").ToString();
  // Mode two 
   string value = "";
  if (!_cache.TryGetValue("NeverExpire", out value))
   {
  throw new Exception(" The cache does not exist or has expired ");
  }
}

Clear cache value

  static void GetCache()
   {
    string value = "";
     if (_cache.TryGetValue("NeverExpire", out value))
     {
      _cache.Remove("NeverExpire");
     }
}

Maybe you found out , We don't need to... When we remove it value value , Then use temporary variables , Is it a little painful ！

Actually C# It's also taken into account , that c# from 7.0 Start to support abandonment , Abandoning yuan is not just a written and semantic improvement , It can also reduce memory allocation .

Simplify the above code

  static void GetCache()
   {
     if (_cache.TryGetValue("NeverExpire", out _))
      {
          _cache.Remove("NeverExpire");
     }
}

Complete code

 class Program
   {
       public static IMemoryCache _cache = new MemoryCache(new MemoryCacheOptions());
       static void Main(string[] args)
       {
           _cache.Get("NeverExpire").ToString();
           string value = "";
           if (!_cache.TryGetValue("NeverExpire", out value))
           {
               throw new Exception(" The cache does not exist or has expired ");
           }
           if (_cache.TryGetValue("NeverExpire", out value))
           {
               _cache.Remove("NeverExpire");
           }
           if (_cache.TryGetValue("NeverExpire", out _))
           {
               _cache.Remove("NeverExpire");
           }
       }

       /// <summary>
       ///  Never expire 
       /// </summary>
       static void NeverExpire()
       {
           _cache.Set("NeverExpire", "1");
       }
       /// <summary>
       ///  Absolute expiration time 
       /// </summary>
       static void AbsoluteExpiration()
       {
           DateTime time = new DateTime(2022, 04, 01, 23, 59, 59);
           _cache.Set("AbsoluteExpiration", "20220401235959", time);
       }
       /// <summary>
       ///  Relative to the current expiration time 
       /// </summary>
       /// 
       static void ExpirationTimeRelativeToThePresent()
       {
           _cache.Set("AbsoluteExpiration", "123456", new TimeSpan(0, 0, 60));
       }
       /// <summary>
       ///  Slide expiration time 
       /// </summary>
       static void SlidingExpirationTime()
       {
           _cache.Set("key3", "3", new MemoryCacheEntryOptions()
           {
               SlidingExpiration = new TimeSpan(0, 0, 2),
               AbsoluteExpiration = DateTimeOffset.Now.AddMilliseconds(1000)
           });
       }
   }

Finally, if you like my article , Please pay attention and praise , hope net The ecosystem is getting better and better ！