Fix for non-uniform random value generators (#26)

* Added failing unit test

* Fix identified. System.Random requires a lock for multithread access

* Issue resolved. Random values are now uniform

* Moved tests to a dedicated folder

src/RandomDataGenerator Solution.sln

@@ -39,6 +39,10 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "RandomDataGenerator.Gui3",
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "ConsoleApp", "ConsoleApp\ConsoleApp.csproj", "{13262322-06A6-4CB7-AABC-78DA60730E07}"
 EndProject
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "tests", "tests", "{51B9C7D7-C306-485A-8EA9-38B32E928E95}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "RandomDataGenerator.Tests", "..\tests\RandomDataGenerator.Tests\RandomDataGenerator.Tests.csproj", "{ED709720-2669-444E-AC90-ABB0B76A894A}"
+EndProject
 Global
  GlobalSection(SolutionConfigurationPlatforms) = preSolution
  Debug|Any CPU = Debug|Any CPU
@@ -77,6 +81,10 @@ Global
  {13262322-06A6-4CB7-AABC-78DA60730E07}.Debug|Any CPU.Build.0 = Debug|Any CPU
  {13262322-06A6-4CB7-AABC-78DA60730E07}.Release|Any CPU.ActiveCfg = Release|Any CPU
  {13262322-06A6-4CB7-AABC-78DA60730E07}.Release|Any CPU.Build.0 = Release|Any CPU
+ {ED709720-2669-444E-AC90-ABB0B76A894A}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+ {ED709720-2669-444E-AC90-ABB0B76A894A}.Debug|Any CPU.Build.0 = Debug|Any CPU
+ {ED709720-2669-444E-AC90-ABB0B76A894A}.Release|Any CPU.ActiveCfg = Release|Any CPU
+ {ED709720-2669-444E-AC90-ABB0B76A894A}.Release|Any CPU.Build.0 = Release|Any CPU
  EndGlobalSection
  GlobalSection(SolutionProperties) = preSolution
  HideSolutionNode = FALSE
@@ -90,6 +98,7 @@ Global
  {94DA986E-B36A-4A9A-8B1E-F5BBAE82BEE7} = {CD43A6FA-4DEF-47B3-A430-9E7FFAD6B035}
  {89571CAF-8CA9-44C2-98AB-D476CA2458DF} = {CD43A6FA-4DEF-47B3-A430-9E7FFAD6B035}
  {13262322-06A6-4CB7-AABC-78DA60730E07} = {F8306255-6F4A-4E70-9932-06B2A3C9DF78}
+ {ED709720-2669-444E-AC90-ABB0B76A894A} = {51B9C7D7-C306-485A-8EA9-38B32E928E95}
  EndGlobalSection
  GlobalSection(ExtensibilityGlobals) = postSolution
  SolutionGuid = {F00DE8F4-BF0D-49C3-8854-600E8142BE41}

src/RandomDataGenerator/Generators/RandomValueGenerator.cs

@@ -13,7 +13,8 @@ namespace RandomDataGenerator.Generators
  internal class RandomValueGenerator
  {
  private const double Tolerance = double.Epsilon;
- private Random _rnf = new();
+ static Random _rnf = new();
+ static readonly object RandomLock = new object();
  private double _storedUniformDeviate;
  private bool _storedUniformDeviateIsGood;
 
@@ -27,7 +28,10 @@ public RandomValueGenerator(int seed)
 
  public void Reset(int seed)
  {
- _rnf = new Random(seed);
+ lock (RandomLock)
+ {
+ _rnf = new Random(seed);
+ }
  }
  #endregion
 
@@ -38,23 +42,32 @@ public void Reset(int seed)
  /// </summary>
  public double Next()
  {
- return _rnf.NextDouble();
+ lock (RandomLock)
+ {
+ return _rnf.NextDouble();
+ }
  }
 
  /// <summary>
  /// Returns true or false randomly.
  /// </summary>
  public bool NextBoolean()
  {
- return _rnf.Next(0, 2) != 0;
+ lock (RandomLock)
+ {
+ return _rnf.Next(0, 2) != 0;
+ }
  }
 
  /// <summary>
  /// Returns double in the range [0, 1)
  /// </summary>
  public double NextDouble()
  {
- return _rnf.NextDouble();
+ lock (RandomLock)
+ {
+ return _rnf.NextDouble();
+ }
  }
 
  /// <summary>
@@ -68,7 +81,10 @@ public byte[] NextBytes(int min, int max)
  int arrayLength = Next(min, max);
 
  byte[] bytes = new byte[arrayLength];
- _rnf.NextBytes(bytes);
+ lock (RandomLock)
+ {
+ _rnf.NextBytes(bytes);
+ }
 
  return bytes;
  }
@@ -140,8 +156,11 @@ public byte Next(byte min, byte max)
  throw new ArgumentException("Max must be greater than min.");
  }
 
- double rn = (max * 1.0 - min * 1.0) * _rnf.NextDouble() + min * 1.0;
- return Convert.ToByte(rn);
+ lock (RandomLock)
+ {
+ double rn = (max * 1.0 - min * 1.0) * _rnf.NextDouble() + min * 1.0;
+ return Convert.ToByte(rn);
+ }
  }
 
  /// <summary>
@@ -154,16 +173,22 @@ public short Next(short min, short max)
  throw new ArgumentException("Max must be greater than min.");
  }
 
- double rn = (max * 1.0 - min * 1.0) * _rnf.NextDouble() + min * 1.0;
- return Convert.ToInt16(rn);
+ lock (RandomLock)
+ {
+ double rn = (max * 1.0 - min * 1.0) * _rnf.NextDouble() + min * 1.0;
+ return Convert.ToInt16(rn);
+ }
  }
 
  /// <summary>
  /// Returns Int32 in the range [min, max)
  /// </summary>
  public int Next(int min, int max)
  {
- return _rnf.Next(min, max);
+ lock (RandomLock)
+ {
+ return _rnf.Next(min, max);
+ }
  }
 
  /// <summary>
@@ -176,8 +201,11 @@ public long Next(long min, long max)
  throw new ArgumentException("Max must be greater than min.");
  }
 
- double rn = (max * 1.0 - min * 1.0) * _rnf.NextDouble() + min * 1.0;
- return Convert.ToInt64(rn);
+ lock (RandomLock)
+ {
+ double rn = (max * 1.0 - min * 1.0) * _rnf.NextDouble() + min * 1.0;
+ return Convert.ToInt64(rn);
+ }
  }
 
  /// <summary>
@@ -190,8 +218,11 @@ public float Next(float min, float max)
  throw new ArgumentException("Max must be greater than min.");
  }
 
- double rn = (max * 1.0 - min * 1.0) * _rnf.NextDouble() + min * 1.0;
- return Convert.ToSingle(rn);
+ lock (RandomLock)
+ {
+ double rn = (max * 1.0 - min * 1.0) * _rnf.NextDouble() + min * 1.0;
+ return Convert.ToSingle(rn);
+ }
  }
 
  /// <summary>
@@ -204,8 +235,11 @@ public double Next(double min, double max)
  throw new ArgumentException("Max must be greater than min.");
  }
 
- double rn = (max - min) * _rnf.NextDouble() + min;
- return rn;
+ lock (RandomLock)
+ {
+ double rn = (max - min) * _rnf.NextDouble() + min;
+ return rn;
+ }
  }
 
  /// <summary>
@@ -220,10 +254,13 @@ public DateTime Next(DateTime min, DateTime max)
 
  long minTicks = min.Ticks;
  long maxTicks = max.Ticks;
- double rn = (Convert.ToDouble(maxTicks)
- - Convert.ToDouble(minTicks)) * _rnf.NextDouble()
- + Convert.ToDouble(minTicks);
- return new DateTime(Convert.ToInt64(rn));
+ lock (RandomLock)
+ {
+ double rn = (Convert.ToDouble(maxTicks)
+ - Convert.ToDouble(minTicks)) * _rnf.NextDouble()
+ + Convert.ToDouble(minTicks);
+ return new DateTime(Convert.ToInt64(rn));
+ }
  }
 
  /// <summary>
@@ -238,10 +275,13 @@ public TimeSpan Next(TimeSpan min, TimeSpan max)
 
  long minTicks = min.Ticks;
  long maxTicks = max.Ticks;
- double rn = (Convert.ToDouble(maxTicks)
- - Convert.ToDouble(minTicks)) * _rnf.NextDouble()
- + Convert.ToDouble(minTicks);
- return new TimeSpan(Convert.ToInt64(rn));
+ lock (RandomLock)
+ {
+ double rn = (Convert.ToDouble(maxTicks)
+ - Convert.ToDouble(minTicks)) * _rnf.NextDouble()
+ + Convert.ToDouble(minTicks);
+ return new TimeSpan(Convert.ToInt64(rn));
+ }
  }
 
  /// <summary>

tests/RandomDataGenerator.Tests/CityRandomizerTests.cs

@@ -0,0 +1,81 @@
+using System.Collections.Concurrent;
+using RandomDataGenerator.FieldOptions;
+using RandomDataGenerator.Randomizers;
+using Xunit.Abstractions;
+
+namespace RandomDataGenerator.Tests
+{
+ public class CityRandomizerTests
+ {
+ private readonly ITestOutputHelper _output;
+ static readonly Random random = new System.Random(420);
+ static readonly object randLock = new object();
+
+ public CityRandomizerTests(ITestOutputHelper output)
+ {
+ this._output = output;
+ }
+
+
+ [Theory]
+ [InlineData(1)]
+ [InlineData(2)]
+ [InlineData(4)]
+ [InlineData(8)]
+ public void CityDistributionMustBeUniform(int degree)
+ {
+ var locationGenerator = RandomizerFactory.GetRandomizer(new FieldOptionsCity { ValueAsString = true, UseNullValues = false });
+ var concurrentDictionary = new ConcurrentDictionary<string, long>();
+ var options = new ParallelOptions { MaxDegreeOfParallelism = degree };
+ Parallel.For(0, 1000, options, i =>
+ {
+ Parallel.For(0, 1000, options, j =>
+ {
+ var location = locationGenerator.Generate();
+ concurrentDictionary.AddOrUpdate(location, _ => 1, (k, v) => v + 1);
+ });
+ });
+ var topCount = concurrentDictionary.OrderByDescending(pair => pair.Value).First();
+ var bottomCount = concurrentDictionary.OrderBy(pair => pair.Value).First();
+ _output.WriteLine($"{topCount}");
+ _output.WriteLine($"{bottomCount}");
+ Assert.True(topCount.Value/bottomCount.Value<2);
+ Assert.NotEqual(topCount.Key, bottomCount.Key);
+ }
+
+ [Fact]
+ public void TwoRandomCitiesMustNotBeTheSame()
+ {
+ var locationGenerator = RandomizerFactory.GetRandomizer(new FieldOptionsCity { ValueAsString = true, UseNullValues = false });
+ var locationOne = locationGenerator.Generate();
+ var locationTwo = locationGenerator.Generate();
+ Assert.NotEqual(locationOne, locationTwo);
+ }
+
+ [Fact]
+ public void SystemRandomDistributionMustBeUniform()
+ {
+ var concurrentDictionary = new ConcurrentDictionary<int, long>();
+ Parallel.For(0, 1000, i =>
+ {
+ Parallel.For(0, 1000, j =>
+ {
+ int index;
+ lock (randLock)
+ {
+ index = random.Next(0, 2000);
+ }
+
+ concurrentDictionary.AddOrUpdate(index, _ => 1, (k, v) => v + 1);
+ });
+ });
+ var topCount = concurrentDictionary.OrderByDescending(pair => pair.Value).First();
+ var bottomCount = concurrentDictionary.OrderBy(pair => pair.Value).First();
+ _output.WriteLine($"{topCount}");
+ _output.WriteLine($"{bottomCount}");
+ Assert.True(topCount.Value / bottomCount.Value < 2);
+ Assert.NotEqual(topCount.Key, bottomCount.Key);
+
+ }
+ }
+}

tests/RandomDataGenerator.Tests/RandomDataGenerator.Tests.csproj

@@ -0,0 +1,28 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+ <PropertyGroup>
+ <TargetFramework>net7.0</TargetFramework>
+ <ImplicitUsings>enable</ImplicitUsings>
+ <Nullable>enable</Nullable>
+
+ <IsPackable>false</IsPackable>
+ </PropertyGroup>
+
+ <ItemGroup>
+ <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.3.2" />
+ <PackageReference Include="xunit" Version="2.4.2" />
+ <PackageReference Include="xunit.runner.visualstudio" Version="2.4.5">
+ <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+ <PrivateAssets>all</PrivateAssets>
+ </PackageReference>
+ <PackageReference Include="coverlet.collector" Version="3.1.2">
+ <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+ <PrivateAssets>all</PrivateAssets>
+ </PackageReference>
+ </ItemGroup>
+
+ <ItemGroup>
+ <ProjectReference Include="..\..\src\RandomDataGenerator\RandomDataGenerator.csproj" />
+ </ItemGroup>
+
+</Project>

tests/RandomDataGenerator.Tests/Usings.cs

@@ -0,0 +1 @@
+global using Xunit;