Make RandomNumberGenerator.Create return a singleton

src/libraries/System.Security.Cryptography.Algorithms/src/Internal/Cryptography/RandomNumberGeneratorImplementation.Windows.cs

@@ -7,6 +7,15 @@ namespace System.Security.Cryptography
 {
  internal sealed partial class RandomNumberGeneratorImplementation
  {
+ // a singleton which always calls into a thread-safe implementation
+ // and whose Dispose method no-ops
+ internal static readonly RandomNumberGeneratorImplementation s_singleton = new RandomNumberGeneratorImplementation();
+
+ // private ctor used only by singleton
+ private RandomNumberGeneratorImplementation()
+ {
+ }
+
  private static unsafe void GetBytes(byte* pbBuffer, int count)
  {
  Debug.Assert(count > 0);

src/libraries/System.Security.Cryptography.Algorithms/src/System/Security/Cryptography/RandomNumberGenerator.cs

@@ -12,10 +12,7 @@ public abstract class RandomNumberGenerator : IDisposable
  {
  protected RandomNumberGenerator() { }
 
- public static RandomNumberGenerator Create()
- {
- return new RandomNumberGeneratorImplementation();
- }
+ public static RandomNumberGenerator Create() => RandomNumberGeneratorImplementation.s_singleton;
 
  [UnsupportedOSPlatform("browser")]
  [RequiresUnreferencedCode(CryptoConfig.CreateFromNameUnreferencedCodeMessage)]

src/libraries/System.Security.Cryptography.Algorithms/tests/RandomNumberGeneratorTests.cs

@@ -12,6 +12,30 @@ namespace System.Security.Cryptography.RNG.Tests
 {
  public class RandomNumberGeneratorTests
  {
+ [Fact]
+ public static void Create_ReturnsSingleton()
+ {
+ RandomNumberGenerator rng1 = RandomNumberGenerator.Create();
+ RandomNumberGenerator rng2 = RandomNumberGenerator.Create();
+
+ Assert.Same(rng1, rng2);
+ }
+
+ [Fact]
+ public static void Singleton_NoopsDispose()
+ {
+ byte[] random = new byte[1024];
+ RandomNumberGenerator rng = RandomNumberGenerator.Create();
+ rng.GetBytes(random);
+ RandomDataGenerator.VerifyRandomDistribution(random);
+ rng.Dispose(); // should no-op if called once
+
+ random = new byte[1024];
+ rng.GetBytes(random); // should still work even after earlier Dispose call
+ RandomDataGenerator.VerifyRandomDistribution(random);
+ rng.Dispose(); // should no-op if called twice
+ }
+
  [Theory]
  [InlineData(2048)]
  [InlineData(65536)]