Replace System.Random with Xorshift RNG. (#13)

Use fast XorShift RNG.

Author: jlao

Benchmark/Eviction.cs

@@ -0,0 +1,35 @@
+using BenchmarkDotNet.Attributes;
+using CacheTable;
+
+namespace Benchmark
+{
+    [ClrJob]
+    [RankColumn]
+    public class Eviction
+    {
+        private CacheTable<WrappedInt, int> cacheTable;
+        private int i;
+
+        [Params(4, 8)]
+        public int N;
+
+        [GlobalSetup]
+        public void Setup()
+        {
+            this.cacheTable = new CacheTable<WrappedInt, int>(10, this.N);
+
+            for (int i = 0; i < this.N; i++)
+            {
+                this.cacheTable[i] = i;
+            }
+
+            this.i = this.N;
+        }
+
+        [Benchmark]
+        public void CacheTable()
+        {
+            this.cacheTable[this.i] = this.i++;
+        }
+    }
+}

Benchmark/GuidKeysReadFullTable.cs

@@ -0,0 +1,86 @@
+using CacheTable;
+using System;
+using BenchmarkDotNet.Attributes;
+using System.Collections.Generic;
+using System.Collections.Concurrent;
+
+namespace Benchmark
+{
+    [CoreJob]
+    [RPlotExporter, RankColumn]
+    public class GuidKeysReadFullTable
+    {
+        private readonly CacheTable<WrappedString, int> cacheTable = new CacheTable<WrappedString, int>(10, 4);
+        private readonly Dictionary<WrappedString, int> dictionary = new Dictionary<WrappedString, int>();
+        private WrappedString[] keys;
+
+        struct WrappedString : IEquatable<WrappedString>
+        {
+            public string Value;
+
+            public bool Equals(WrappedString other) => this.Value.Equals(other.Value);
+
+            public override int GetHashCode() => this.Value.GetHashCode();
+
+            public override bool Equals(object obj) => this.Equals((WrappedString)obj);
+
+            public static implicit operator WrappedString(string str) => new WrappedString { Value = str };
+        }
+
+        [GlobalSetup]
+        public void Setup()
+        {
+            while (cacheTable.Count != 40)
+            {
+                this.cacheTable[Guid.NewGuid().ToString()] = 42;
+            }
+
+            this.keys = new WrappedString[40];
+            int i = 0;
+            foreach (KeyValuePair<WrappedString, int> kvp in cacheTable)
+            {
+                this.dictionary[kvp.Key] = kvp.Value;
+                this.keys[i++] = kvp.Key;
+            }
+
+            Random rng = new Random();
+            Shuffle(rng, this.keys);
+        }
+
+        public static void Shuffle<T>(Random rng, T[] array)
+        {
+            int n = array.Length;
+            while (n > 1)
+            {
+                int k = rng.Next(n--);
+                T temp = array[n];
+                array[n] = array[k];
+                array[k] = temp;
+            }
+        }
+
+        [Benchmark]
+        public int CacheTable()
+        {
+            int sum = 0;
+            foreach (var k in this.keys)
+            {
+                sum += this.cacheTable[k];
+            }
+
+            return sum;
+        }
+
+        [Benchmark(Baseline = true)]
+        public int Dictionary()
+        {
+            int sum = 0;
+            foreach (var k in this.keys)
+            {
+                sum += this.dictionary[k];
+            }
+
+            return sum;
+        }
+    }
+}

Benchmark/HashCollisions.cs

@@ -15,41 +15,31 @@ public class HashCollisions
         private readonly Dictionary<WrappedInt, int> dictionary = new Dictionary<WrappedInt, int>();
         private readonly ConcurrentDictionary<WrappedInt, int> concurrentDictionary = new ConcurrentDictionary<WrappedInt, int>();
 
-        struct WrappedInt : IEquatable<WrappedInt>
-        {
-            public int Value;
-
-            public bool Equals(WrappedInt other) => this.Value == other.Value;
-
-            public override int GetHashCode() => 42;
-
-            public override bool Equals(object obj) => this.Equals((WrappedInt)obj);
-
-            public static implicit operator WrappedInt(int i) => new WrappedInt { Value = i };
-        }
+        [Params(32, 64)]
+        public int N;
 
         [Benchmark]
         public void CacheTable()
         {
-            for (int i = 0; i < 4; i++) this.cacheTable[i] = i;
+            for (int i = 0; i < this.N; i++) this.cacheTable[i] = i;
         }
 
-        [Benchmark]
-        public void ConcurrentCacheTable()
+        [Benchmark(Baseline = true)]
+        public void Dictionary()
         {
-            for (int i = 0; i < 4; i++) this.concurrentCacheTable[i] = i;
+            for (int i = 0; i < this.N; i++) this.dictionary[i] = i;
         }
 
-        [Benchmark(Baseline = true)]
-        public void Dictionary()
+        [Benchmark]
+        public void ConcurrentCacheTable()
         {
-            for (int i = 0; i < 4; i++) this.dictionary[i] = i;
+            for (int i = 0; i < this.N; i++) this.concurrentCacheTable[i] = i;
         }
 
         [Benchmark]
         public void ConcurrentDictionary()
         {
-            for (int i = 0; i < 4; i++) this.concurrentDictionary[i] = i;
+            for (int i = 0; i < this.N; i++) this.concurrentDictionary[i] = i;
         }
     }
 }

Benchmark/RngPerf.cs

@@ -0,0 +1,26 @@
+using BenchmarkDotNet.Attributes;
+using CacheTable;
+using System;
+
+namespace Benchmark
+{
+    [CoreJob]
+    [RankColumn]
+    public class RngPerf
+    {
+        private readonly Random random = new Random();
+        private readonly XorShiftRandom xorshift = new XorShiftRandom();
+        
+        [Benchmark(Baseline = true)]
+        public int Random()
+        {
+            return this.random.Next(12);
+        }
+
+        [Benchmark]
+        public int XortShiftRandom()
+        {
+            return this.xorshift.Next(12);
+        }
+    }
+}

Benchmark/WrappedInt.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace Benchmark
+{
+    struct WrappedInt : IEquatable<WrappedInt>
+    {
+        public int Value;
+
+        public bool Equals(WrappedInt other) => this.Value == other.Value;
+
+        public override int GetHashCode() => 42;
+
+        public override bool Equals(object obj) => this.Equals((WrappedInt)obj);
+
+        public static implicit operator WrappedInt(int i) => new WrappedInt { Value = i };
+    }
+}

CacheTable/CacheTable.cs

@@ -14,7 +14,7 @@ public class CacheTable<TKey, TValue> : ICacheTable<TKey, TValue>
     {
         private CacheTableInternal<TKey, TValue> table;
         private int count;
-        private readonly Random rng = new Random();
+        private readonly XorShiftRandom rng = new XorShiftRandom();
 
         /// <summary>
         /// Creates a set associative cache with specified number of rows and columns.

CacheTable/CacheTableInternal.cs

@@ -106,7 +106,7 @@ public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
         }
 
         // Returns true if item was inserted into empty slot. False otherwise.
-        public bool Set(TKey key, TValue value, int row, Random rng)
+        public bool Set(TKey key, TValue value, int row, XorShiftRandom rng)
         {
             (int rowStart, int rowEnd) = this.GetRowRange(row);
             int empty = -1;

CacheTable/ConcurrentCacheTable.cs

@@ -15,7 +15,7 @@ public class ConcurrentCacheTable<TKey, TValue> : ICacheTable<TKey, TValue>
     {
         private readonly CacheTableInternal<TKey, TValue> table;
         private readonly object[] lockObjects;
-        private readonly Random[] rngs;
+        private readonly XorShiftRandom[] rngs;
         private readonly int[] counts;
 
         /// <summary>
@@ -35,10 +35,10 @@ public ConcurrentCacheTable(int rows, int columns, int concurrency)
                 this.lockObjects[i] = new object();
             }
 
-            this.rngs = new Random[concurrency];
+            this.rngs = new XorShiftRandom[concurrency];
             for (int i = 0; i < concurrency; i++)
             {
-                this.rngs[i] = new Random();
+                this.rngs[i] = new XorShiftRandom();
             }
         }
 
@@ -248,7 +248,7 @@ private object GetLockObjectForRow(int row)
             return this.lockObjects[row % this.lockObjects.Length];
         }
 
-        private Random GetRng(int row)
+        private XorShiftRandom GetRng(int row)
         {
             return this.rngs[row % this.rngs.Length];
         }

CacheTable/XorShiftRandom.cs

@@ -0,0 +1,50 @@
+using System;
+using System.Runtime.CompilerServices;
+
+namespace CacheTable
+{
+    public class XorShiftRandom
+    {
+        [ThreadStatic]
+        private static Random seedRng;
+
+        private uint state;
+
+        public XorShiftRandom() : this(GetNonZeroSeed())
+        {
+        }
+
+        public XorShiftRandom(uint seed)
+        {
+            this.state = seed;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public int Next(int max)
+        {
+            uint x = this.state;
+            x ^= x << 13;
+            x ^= x >> 17;
+            x ^= x << 5;
+            this.state = x;
+            return (int)(x % max);
+        }
+
+        private static uint GetNonZeroSeed()
+        {
+            if (seedRng == null)
+            {
+                seedRng = new Random();
+            }
+
+            while (true)
+            {
+                uint seed = (uint)seedRng.Next();
+                if (seed != 0)
+                {
+                    return seed;
+                }
+            }
+        }
+    }
+}