Imported Upstream version 4.0.0~alpha1

Former-commit-id: 806294f5ded97629b74c85c09952f2a74fe182d9

mcs/class/System.Runtime.Caching/ReferenceSources/CacheUsage.cs

@@ -0,0 +1,82 @@
+// This file implements the classes UsageEntryRef and CacheUsage missing from .NET reference source
+
+namespace System.Runtime.Caching {
+	class UsageEntryRef {
+		public static UsageEntryRef INVALID = new UsageEntryRef ();
+
+		public bool IsInvalid {
+			get { return this == INVALID; }
+		}
+
+		// This is used to compare MemoryCacheEntry that have the same UtcLastUpdateUsage.
+		public int DateTimeIndex {
+			get; set;
+		}
+	}
+
+	class CacheUsageHelper : ICacheEntryHelper
+	{
+		public int Compare(MemoryCacheEntry entry1, MemoryCacheEntry entry2)
+		{
+			var ret = DateTime.Compare (entry1.UtcLastUpdateUsage , entry2.UtcLastUpdateUsage);
+			if (ret == 0)
+				return entry1.UsageEntryRef.DateTimeIndex - entry2.UsageEntryRef.DateTimeIndex;
+
+			return ret;
+		}
+
+		public DateTime GetDateTime (MemoryCacheEntry entry)
+		{
+			return entry.UtcLastUpdateUsage;
+		}
+	}
+
+	class CacheUsage : CacheEntryCollection {
+
+		public static TimeSpan CORRELATED_REQUEST_TIMEOUT = new TimeSpan (0, 0, 10);
+		public static TimeSpan MIN_LIFETIME_FOR_USAGE = new TimeSpan (0, 0, 10);
+		public static CacheUsageHelper helper = new CacheUsageHelper ();
+
+		public DateTime prevDateTime;
+		public int dateTimeIndex;
+
+		public CacheUsage (MemoryCacheStore store)
+			: base (store, helper)
+		{
+		}
+
+		public void Add (MemoryCacheEntry entry)
+		{
+			var now = DateTime.UtcNow;
+			if (now == prevDateTime)
+				dateTimeIndex++;
+			else
+				dateTimeIndex = 0;
+
+			prevDateTime = now;
+
+			entry.UtcLastUpdateUsage = now;
+			entry.UsageEntryRef = new UsageEntryRef ();
+			entry.UsageEntryRef.DateTimeIndex = dateTimeIndex;
+			base.Add (entry);
+		}
+
+		public void Remove (MemoryCacheEntry entry)
+		{
+			base.Remove (entry);
+			entry.UsageEntryRef = UsageEntryRef.INVALID;
+		}
+
+		public void Update (MemoryCacheEntry entry)
+		{
+			base.Remove (entry);
+			entry.UtcLastUpdateUsage = DateTime.UtcNow;
+			base.Add (entry);
+		}
+
+		public int FlushUnderUsedItems (int count)
+		{
+			return base.FlushItems (DateTime.MaxValue, CacheEntryRemovedReason.Evicted, true, count);
+		}
+	}
+}