Add Random.Shared

src/libraries/Common/tests/StreamConformanceTests/System/IO/StreamConformanceTests.cs

@@ -2240,7 +2240,7 @@ public virtual async Task ReadWrite_CustomMemoryManager_Success(bool useAsync)
                 Assert.Equal(1024, writeBuffer.Memory.Length);
                 Assert.Equal(writeBuffer.Memory.Length, readBuffer.Memory.Length);
 
-                new Random().NextBytes(writeBuffer.Memory.Span);
+                Random.Shared.NextBytes(writeBuffer.Memory.Span);
                 readBuffer.Memory.Span.Clear();
 
                 Task write = useAsync ?

src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/ConcurrentStack.cs

@@ -606,7 +606,6 @@ private int TryPopCore(int count, out Node? poppedHead)
             Node? head;
             Node next;
             int backoff = 1;
-            Random? r = null;
             while (true)
             {
                 head = _head;
@@ -649,11 +648,7 @@ private int TryPopCore(int count, out Node? poppedHead)
 
                 if (spin.NextSpinWillYield)
                 {
-                    if (r == null)
-                    {
-                        r = new Random();
-                    }
-                    backoff = r.Next(1, BACKOFF_MAX_YIELDS);
+                    backoff = Random.Shared.Next(1, BACKOFF_MAX_YIELDS);
                 }
                 else
                 {

src/libraries/System.IO.Compression.Brotli/tests/CompressionStreamUnitTests.Brotli.cs

@@ -177,7 +177,7 @@ public void RoundTrip_Chunks()
             for (int i = 0; i < totalSize; i += chunkSize)
             {
                 byte[] uncompressed = new byte[chunkSize];
-                new Random().NextBytes(uncompressed);
+                Random.Shared.NextBytes(uncompressed);
                 byte[] compressed = new byte[BrotliEncoder.GetMaxCompressedLength(chunkSize)];
                 byte[] decompressed = new byte[chunkSize];
                 var uncompressedSpan = new ReadOnlySpan<byte>(uncompressed);

src/libraries/System.Net.Mail/tests/Functional/LoopbackSmtpServer.cs

@@ -26,7 +26,7 @@ public class LoopbackSmtpServer : IDisposable
         private bool _disposed = false;
         private readonly Socket _listenSocket;
         private readonly ConcurrentBag<Socket> _socketsToDispose;
-        private long _messageCounter = new Random().Next(1000, 2000);
+        private long _messageCounter = Random.Shared.Next(1000, 2000);
 
         public readonly int Port;
         public SmtpClient CreateClient() => new SmtpClient("localhost", Port);

src/libraries/System.Net.Ping/src/System/Net/NetworkInformation/Ping.Unix.cs

@@ -20,8 +20,6 @@ public partial class Ping
         private const int MaxIpHeaderLengthInBytes = 60;
         private static bool SendIpHeader => OperatingSystem.IsMacOS();
         private static bool NeedsConnect => OperatingSystem.IsLinux();
-        [ThreadStatic]
-        private static Random? t_idGenerator;
 
         private PingReply SendPingCore(IPAddress address, byte[] buffer, int timeout, PingOptions? options)
         {
@@ -51,8 +49,7 @@ private unsafe SocketConfig GetSocketConfig(IPAddress address, byte[] buffer, in
         {
             // Use a random value as the identifier. This doesn't need to be perfectly random
             // or very unpredictable, rather just good enough to avoid unexpected conflicts.
-            Random rand = t_idGenerator ??= new Random();
-            ushort id = (ushort)rand.Next(ushort.MaxValue + 1);
+            ushort id = (ushort)Random.Shared.Next(ushort.MaxValue + 1);
             IpHeader iph = default;
 
             bool ipv4 = address.AddressFamily == AddressFamily.InterNetwork;

src/libraries/System.Net.Quic/tests/FunctionalTests/QuicStreamTests.cs

@@ -435,7 +435,7 @@ private static async Task SendAndReceiveEOFAsync(QuicStream s1, QuicStream s2)
         public async Task ReadWrite_Random_Success(int readSize, int writeSize)
         {
             byte[] testBuffer = new byte[8192];
-            new Random().NextBytes(testBuffer);
+            Random.Shared.NextBytes(testBuffer);
 
             await RunClientServer(
                 async clientConnection =>

src/libraries/System.Net.Security/tests/FunctionalTests/SslStreamNetworkStreamTest.cs

@@ -242,8 +242,7 @@ public async Task SslStream_TargetHostName_Succeeds(bool useEmptyName)
         [ActiveIssue("https://github.com/dotnet/runtime/issues/46837", TestPlatforms.OSX)]
         public async Task SslStream_UntrustedCaWithCustomCallback_OK(bool usePartialChain)
         {
-            var rnd = new Random();
-            int split = rnd.Next(0, certificates.serverChain.Count - 1);
+            int split = Random.Shared.Next(0, certificates.serverChain.Count - 1);
 
             var clientOptions = new  SslClientAuthenticationOptions() { TargetHost = "localhost" };
             clientOptions.RemoteCertificateValidationCallback =

src/libraries/System.Net.Sockets/tests/FunctionalTests/SocketAsyncEventArgsTest.cs

@@ -561,7 +561,7 @@ public void AcceptAsync_WithReceiveBuffer_Success()
                 const int acceptBufferSize = acceptBufferOverheadSize + acceptBufferDataSize;
 
                 byte[] sendBuffer = new byte[acceptBufferDataSize];
-                new Random().NextBytes(sendBuffer);
+                Random.Shared.NextBytes(sendBuffer);
 
                 SocketAsyncEventArgs acceptArgs = new SocketAsyncEventArgs();
                 acceptArgs.Completed += OnAcceptCompleted;

src/libraries/System.Net.Sockets/tests/FunctionalTests/UnixDomainSocketTest.cs

@@ -16,7 +16,6 @@ namespace System.Net.Sockets.Tests
     public class UnixDomainSocketTest
     {
         private readonly ITestOutputHelper _log;
-        private static Random _random = new Random();
 
         public UnixDomainSocketTest(ITestOutputHelper output)
         {
@@ -251,7 +250,7 @@ public async Task Socket_SendReceiveAsync_Success()
         public async Task Socket_SendReceiveAsync_PropagateToStream_Success(int iterations, int writeBufferSize, int readBufferSize)
         {
             var writeBuffer = new byte[writeBufferSize * iterations];
-            new Random().NextBytes(writeBuffer);
+            Random.Shared.NextBytes(writeBuffer);
             var readData = new MemoryStream();
 
             string path = GetRandomNonExistingFilePath();
@@ -317,7 +316,7 @@ public async Task ConcurrentSendReceive(bool forceNonBlocking)
                 const int Iters = 25;
                 byte[] sendData = new byte[Iters];
                 byte[] receiveData = new byte[sendData.Length];
-                new Random().NextBytes(sendData);
+                Random.Shared.NextBytes(sendData);
 
                 string path = GetRandomNonExistingFilePath();
 
@@ -359,7 +358,7 @@ public async Task ConcurrentSendReceiveAsync()
                 const int Iters = 2048;
                 byte[] sendData = new byte[Iters];
                 byte[] receiveData = new byte[sendData.Length];
-                new Random().NextBytes(sendData);
+                Random.Shared.NextBytes(sendData);
 
                 string path = GetRandomNonExistingFilePath();
 
@@ -498,7 +497,7 @@ private static string GetRandomNonExistingFilePath()
             do
             {
                 // get random name and append random number of characters to get variable name length.
-                result = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName() + new string('A', _random.Next(1, 32)));
+                result = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName() + new string('A', Random.Shared.Next(1, 32)));
             }
             while (File.Exists(result));
 

src/libraries/System.Net.WebClient/tests/WebClientTest.cs

@@ -660,11 +660,8 @@ public async Task UploadData_LargeData_Success(Uri server)
             byte[] ignored = await UploadDataAsync(wc, server.ToString(), Encoding.UTF8.GetBytes(largeText));
         }
 
-        private static string GetRandomText(int length)
-        {
-            var rand = new Random();
-            return new string(Enumerable.Range(0, 512 * 1024).Select(_ => (char)('a' + rand.Next(0, 26))).ToArray());
-        }
+        private static string GetRandomText(int length) =>
+            new string(Enumerable.Range(0, 512 * 1024).Select(_ => (char)('a' + Random.Shared.Next(0, 26))).ToArray());
 
         [OuterLoop("Uses external servers")]
         [Theory]

src/libraries/System.Net.WebSockets.Client/tests/SendReceiveTest.cs

@@ -91,9 +91,8 @@ public async Task SendReceive_PartialMessageDueToSmallReceiveBuffer_Success(Uri
         [PlatformSpecific(~TestPlatforms.Browser)]  // JS Websocket does not support see issue https://github.com/dotnet/runtime/issues/46983
         public async Task SendReceive_PartialMessageBeforeCompleteMessageArrives_Success(Uri server)
         {
-            var rand = new Random();
             var sendBuffer = new byte[ushort.MaxValue + 1];
-            rand.NextBytes(sendBuffer);
+            Random.Shared.NextBytes(sendBuffer);
             var sendSegment = new ArraySegment<byte>(sendBuffer);
 
             // Ask the remote server to echo back received messages without ever signaling "end of message".
@@ -464,7 +463,6 @@ public async Task ZeroByteReceive_CompletesWhenDataAvailable(Uri server)
         {
             using (ClientWebSocket cws = await WebSocketHelper.GetConnectedWebSocket(server, TimeOutMilliseconds, _output))
             {
-                var rand = new Random();
                 var ctsDefault = new CancellationTokenSource(TimeOutMilliseconds);
 
                 // Do a 0-byte receive.  It shouldn't complete yet.

src/libraries/System.Numerics.Vectors/tests/GenericVectorTests.cs

@@ -716,7 +716,7 @@ static GenericVectorTests()
             // us to check that we didn't overwrite any part of the destination
             // if it was too small to contain the entire output.
 
-            new Random().NextBytes(MemoryMarshal.AsBytes(destination));
+            Random.Shared.NextBytes(MemoryMarshal.AsBytes(destination));
             T[] destinationCopy = destination.ToArray();
 
             Assert.False(vector.TryCopyTo(destination.Slice(1)));

src/libraries/System.Private.CoreLib/src/System/Numerics/Hashing/HashHelpers.cs

@@ -5,8 +5,6 @@ namespace System.Numerics.Hashing
 {
     internal static class HashHelpers
     {
-        public static readonly int RandomSeed = new Random().Next(int.MinValue, int.MaxValue);
-
         public static int Combine(int h1, int h2)
         {
             // RyuJIT optimizes this to use the ROL instruction

src/libraries/System.Private.CoreLib/src/System/Random.cs

@@ -1,6 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics;
+using System.Runtime.CompilerServices;
+
 namespace System
 {
     /// <summary>
@@ -36,6 +39,17 @@ public partial class Random
             // previously output continues to be output.
             _impl = new LegacyImpl(this, Seed);
 
+        /// <summary>Constructor used by <see cref="ThreadSafeRandom"/>.</summary>
+        /// <param name="isThreadSafeRandom">Must be true.</param>
+        protected private Random(bool isThreadSafeRandom)
+        {
+            Debug.Assert(isThreadSafeRandom);
+            _impl = null!; // base implementation isn't used at all
+        }
+
+        /// <summary>Provides a thread-safe <see cref="Random"/> instance that may be used concurrently from any thread.</summary>
+        public static Random Shared { get; } = new ThreadSafeRandom();
+
         /// <summary>Returns a non-negative random integer.</summary>
         /// <returns>A 32-bit signed integer that is greater than or equal to 0 and less than <see cref="int.MaxValue"/>.</returns>
         public virtual int Next() => _impl.Next();
@@ -148,5 +162,94 @@ public virtual void NextBytes(byte[] buffer)
 
         private static void ThrowMinMaxValueSwapped() =>
             throw new ArgumentOutOfRangeException("minValue", SR.Format(SR.Argument_MinMaxValue, "minValue", "maxValue"));
+
+        /// <summary>Random implementation that delegates all calls to a ThreadStatic Impl instance.</summary>
+        private sealed class ThreadSafeRandom : Random
+        {
+            // We need Random.Shared to return an instance that is thread-safe, as it may be used from multiple threads.
+            // It's also possible that one thread could retrieve Shared and pass it to another thread, so Shared can't
+            // just access a ThreadStatic to return a Random instance stored there.  As such, we need the instance
+            // returned from Shared itself to be thread-safe, which can be accomplished either by locking around all
+            // accesses or by itself accessing a ThreadStatic on every access: we've chosen the latter, as it is more
+            // scalable.  With that, we have two basic approaches:
+            // 1. the instance returned can be a base Random instance constructed with an _impl that is a ThreadSafeImpl.
+            // 2. the instance returned can be a special Random-derived instance, where _impl is ignored and the derived
+            //    type overrides all methods on the base.
+            // (1) is cleaner, as (2) requires duplicating a bit more code, but (2) enables all virtual dispatch to be
+            // devirtualized and potentially inlined, so that Random.Shared.NextXx(...) ends up being faster.
+            // This implements (2).
+
+            [ThreadStatic]
+            private static XoshiroImpl? t_random;
+
+            public ThreadSafeRandom() : base(isThreadSafeRandom: true) { }
+
+            private static XoshiroImpl LocalRandom => t_random ?? Create();
+
+            [MethodImpl(MethodImplOptions.NoInlining)]
+            private static XoshiroImpl Create() => t_random = new();
+
+            public override int Next() => LocalRandom.Next();
+
+            public override int Next(int maxValue)
+            {
+                if (maxValue < 0)
+                {
+                    ThrowMaxValueMustBeNonNegative();
+                }
+
+                return LocalRandom.Next(maxValue);
+            }
+
+            public override int Next(int minValue, int maxValue)
+            {
+                if (minValue > maxValue)
+                {
+                    ThrowMinMaxValueSwapped();
+                }
+
+                return LocalRandom.Next(minValue, maxValue);
+            }
+
+            public override long NextInt64() => LocalRandom.NextInt64();
+
+            public override long NextInt64(long maxValue)
+            {
+                if (maxValue < 0)
+                {
+                    ThrowMaxValueMustBeNonNegative();
+                }
+
+                return LocalRandom.NextInt64(maxValue);
+            }
+
+            public override long NextInt64(long minValue, long maxValue)
+            {
+                if (minValue > maxValue)
+                {
+                    ThrowMinMaxValueSwapped();
+                }
+
+                return LocalRandom.NextInt64(minValue, maxValue);
+            }
+
+            public override float NextSingle() => LocalRandom.NextSingle();
+
+            public override double NextDouble() => LocalRandom.NextDouble();
+
+            public override void NextBytes(byte[] buffer)
+            {
+                if (buffer is null)
+                {
+                    ThrowHelper.ThrowArgumentNullException(ExceptionArgument.buffer);
+                }
+
+                LocalRandom.NextBytes(buffer);
+            }
+
+            public override void NextBytes(Span<byte> buffer) => LocalRandom.NextBytes(buffer);
+
+            protected override double Sample() => throw new NotSupportedException();
+        }
     }
 }

src/libraries/System.Private.Xml/tests/XmlReaderLib/CXMLGeneralTest.cs

@@ -237,7 +237,7 @@ public bool CheckCanReadBinaryContent()
                 try
                 {
                     int nBytes = 0;
-                    switch ((int)new Random().Next(4))
+                    switch ((int)Random.Shared.Next(4))
                     {
                         case 0:
                             CError.WriteLineIgnore("Selecting RCABH");

src/libraries/System.Runtime.Extensions/tests/System/Environment.ExpandEnvironmentVariables.cs

@@ -27,8 +27,7 @@ public void ExpansionOfVariableSucceeds()
             // envvar1=animal;
             // and we are going to check that the expanded %envvar1% is animal.
 
-            Random r = new Random();
-            string envVar1 = "TestVariable_ExpansionOfVariableSucceeds_" + r.Next().ToString();
+            string envVar1 = "TestVariable_ExpansionOfVariableSucceeds_" + Random.Shared.Next().ToString();
             string expectedValue = "animal";
 
             try

src/libraries/System.Runtime.Extensions/tests/System/Environment.GetEnvironmentVariable.cs

@@ -102,9 +102,8 @@ public void VariableNamesAreCaseInsensitiveAsAppropriate()
         [Fact]
         public void CanGetAllVariablesIndividually()
         {
-            Random r = new Random();
-            string envVar1 = "TestVariable_CanGetVariablesIndividually_" + r.Next().ToString();
-            string envVar2 = "TestVariable_CanGetVariablesIndividually_" + r.Next().ToString();
+            string envVar1 = "TestVariable_CanGetVariablesIndividually_" + Random.Shared.Next().ToString();
+            string envVar2 = "TestVariable_CanGetVariablesIndividually_" + Random.Shared.Next().ToString();
 
             try
             {