Setting stopwatch policy TTL to TimeSpan.MaxValue gives invalid TTL (#336)

* max ttl

* fix stopwatch

* testmac

* common max

* mul

* rem

* rem

* mul

---------

Author: bitfaster

BitFaster.Caching.UnitTests/Lru/TLruTickCount64PolicyTests .cs

@@ -2,9 +2,6 @@
 using FluentAssertions.Extensions;
 using BitFaster.Caching.Lru;
 using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
 using System.Threading.Tasks;
 using Xunit;
 
@@ -25,7 +22,7 @@ public void WhenTtlIsTimeSpanMaxThrow()
         [Fact]
         public void WhenTtlIsZeroThrow()
         {
-            Action constructor = () => { new TLruTickCount64Policy<int, int>(TimeSpan.MaxValue); };
+            Action constructor = () => { new TLruTickCount64Policy<int, int>(TimeSpan.Zero); };
 
             constructor.Should().Throw<ArgumentOutOfRangeException>();
         }

BitFaster.Caching.UnitTests/Lru/TlruStopwatchPolicyTests.cs

@@ -11,6 +11,31 @@ public class TlruStopwatchPolicyTests
     {
         private readonly TlruStopwatchPolicy<int, int> policy = new TlruStopwatchPolicy<int, int>(TimeSpan.FromSeconds(10));
 
+        [Fact]
+        public void WhenTtlIsZeroThrow()
+        {
+            Action constructor = () => { new TlruStopwatchPolicy<int, int>(TimeSpan.Zero); };
+
+            constructor.Should().Throw<ArgumentOutOfRangeException>();
+        }
+
+        [Fact]
+        public void WhenTtlIsTimeSpanMaxThrow()
+        {
+            Action constructor = () => { new TlruStopwatchPolicy<int, int>(TimeSpan.MaxValue); };
+
+            constructor.Should().Throw<ArgumentOutOfRangeException>();
+        }
+
+        [Fact]
+        public void WhenTtlIsCloseToMaxAllow()
+        {
+            double maxTicks = long.MaxValue / 100.0d;
+            var ttl = TimeSpan.FromTicks((long)maxTicks) - TimeSpan.FromTicks(10);
+
+            new TlruStopwatchPolicy<int, int>(ttl).TimeToLive.Should().BeCloseTo(ttl, TimeSpan.FromTicks(20));
+        }
+
         [Fact]
         public void TimeToLiveShouldBeTenSecs()
         {

BitFaster.Caching/Lru/TlruStopwatchPolicy.cs

@@ -128,6 +128,16 @@ public ItemDestination RouteCold(LongTickCountLruItem<K, V> item)
         /// <returns>The time represented as ticks.</returns>
         public static long ToTicks(TimeSpan timespan)
         {
+            // mac adjustment factor is 100, giving lowest maximum TTL on mac platform - use same upper limit on all platforms for consistency
+            // this also avoids overflow when multipling long.MaxValue by 1.0
+            double maxTicks = long.MaxValue * 0.01d;
+
+            if (timespan <= TimeSpan.Zero || timespan.Ticks >= maxTicks)
+            {
+                TimeSpan maxRepresentable = TimeSpan.FromTicks((long)maxTicks);
+                Ex.ThrowArgOutOfRange(nameof(timespan), $"Value must be greater than zero and less than {maxRepresentable}");
+            }
+
             return (long)(timespan.Ticks * stopwatchAdjustmentFactor);
         }
 
@@ -137,7 +147,7 @@ public static long ToTicks(TimeSpan timespan)
         /// <param name="ticks">The time represented as ticks.</param>
         /// <returns>The time represented as a TimeSpan.</returns>
         public static TimeSpan FromTicks(long ticks)
-        { 
+        {
             return TimeSpan.FromTicks((long)(ticks / stopwatchAdjustmentFactor));
         }
     }

BitFaster.Caching/Lru/TlruTickCount64Policy.cs

@@ -27,7 +27,7 @@ namespace BitFaster.Caching.Lru
         public TLruTickCount64Policy(TimeSpan timeToLive)
         {
             TimeSpan maxRepresentable = TimeSpan.FromTicks(9223372036854769664);
-            if (timeToLive < TimeSpan.Zero || timeToLive > maxRepresentable)
+            if (timeToLive <= TimeSpan.Zero || timeToLive > maxRepresentable)
             {
                 Ex.ThrowArgOutOfRange(nameof(timeToLive), $"Value must greater than zero and less than {maxRepresentable}");
             }