example.cs

static Meter s_meter = new Meter("Microsoft.Extensions.Caching.Memory.MemoryCache", "1.0.0");
static IMemoryCache? mc1;
static IMemoryCache? mc2;

static void Main(string[] args)
{
   s_meter.CreateObservableGauge<long>("cache-hits", GetCacheHits);
   mc1 = new MemoryCache(new MemoryCacheOptions() { TrackStatistics = true, SizeLimit = 30 });
   mc2 = new MemoryCache(new MemoryCacheOptions() { TrackStatistics = true, SizeLimit = 30 });

   // call to: mc1.TryGetValue(key1, out object? value)
   // or: mc2.TryGetValue(key2, out value2)
   // increments TotalHits
}

// metrics callback for cache hits
static IEnumerable<Measurement<long>> GetCacheHits()
{
   return new Measurement<long>[]
   {
      new Measurement<long>(mc1!.GetCurrentStatistics()!.TotalHits, new KeyValuePair<string,object?>("CacheName", "mc1")),
      new Measurement<long>(mc2!.GetCurrentStatistics()!.TotalHits, new KeyValuePair<string,object?>("CacheName", "mc2")),
   };