CachePolicy supports TryTrimExpired (#470)

Author: bitfaster

BitFaster.Caching.UnitTests/CachePolicyTests.cs

@@ -1,9 +1,4 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
-using FluentAssertions;
+using FluentAssertions;
 using Moq;
 using Xunit;
 
@@ -21,6 +16,33 @@ public void WhenCtorFieldsAreAssigned()
 
             cp.Eviction.Value.Should().Be(eviction.Object);
             cp.ExpireAfterWrite.Value.Should().Be(expire.Object);
+            cp.ExpireAfterAccess.HasValue.Should().BeFalse();
+        }
+
+        [Fact]
+        public void TryTrimWhenTrimNotSupportedReturnsFalse()
+        {
+            var cp = new CachePolicy(Optional<IBoundedPolicy>.None(), Optional<ITimePolicy>.None());
+
+            cp.TryTrimExpired().Should().BeFalse();
+        }
+
+        [Fact]
+        public void TryTrimWhenExpireAfterWriteReturnsTrue()
+        {
+            var expire = new Mock<ITimePolicy>();
+            var cp = new CachePolicy(Optional<IBoundedPolicy>.None(), new Optional<ITimePolicy>(expire.Object));
+
+            cp.TryTrimExpired().Should().BeTrue();
+        }
+
+        [Fact]
+        public void TryTrimWhenExpireAfterAccessReturnsTrue()
+        {
+            var expire = new Mock<ITimePolicy>();
+            var cp = new CachePolicy(Optional<IBoundedPolicy>.None(), Optional<ITimePolicy>.None(), new Optional<ITimePolicy>(expire.Object));
+
+            cp.TryTrimExpired().Should().BeTrue();
         }
     }
 }

BitFaster.Caching/CachePolicy.cs

@@ -16,6 +16,7 @@ public CachePolicy(Optional<IBoundedPolicy> eviction, Optional<ITimePolicy> expi
         {
             this.Eviction = eviction;
             this.ExpireAfterWrite = expireAfterWrite;
+            this.ExpireAfterAccess = Optional<ITimePolicy>.None();
         }
 
         /// <summary>
@@ -48,5 +49,26 @@ public CachePolicy(Optional<IBoundedPolicy> eviction, Optional<ITimePolicy> expi
         /// fixed duration since an entry's creation or most recent read/write access.
         /// </summary>
         public Optional<ITimePolicy> ExpireAfterAccess { get; }
+
+        /// <summary>
+        /// If supported, trim expired items from the cache.
+        /// </summary>
+        /// <returns>True if expiry is supported and expired items were trimmed, otherwise false.</returns>
+        public bool TryTrimExpired()
+        {
+            if (ExpireAfterWrite.HasValue)
+            {
+                ExpireAfterWrite.Value.TrimExpired();
+                return true;
+            }
+
+            if (ExpireAfterAccess.HasValue)
+            {
+                ExpireAfterAccess.Value.TrimExpired();
+                return true;
+            }
+
+            return false;
+        }
     }
 }