Add port sharing support to PlatformBenchmarks on Linux

Author: halter73

src/BenchmarksApps/TechEmpower/PlatformBenchmarks/Program.cs

@@ -2,10 +2,13 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Net;
+using System.Net.Sockets;
 using System.Runtime.InteropServices;
 using System.Text;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets;
 using Microsoft.Extensions.Configuration;
 #if DATABASE
 using Npgsql;
@@ -106,6 +109,32 @@ public static IWebHost BuildWebHost(string[] args)
                 if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
                 {
                     options.UnsafePreferInlineScheduling = Environment.GetEnvironmentVariable("DOTNET_SYSTEM_NET_SOCKETS_INLINE_COMPLETIONS") == "1";
+
+                    // Allow multiple processes bind to the same port. This also "works" on Windows in that it will
+                    // prevent address in use errors and hand off to another process if no others are available,
+                    // but it wouldn't round-robin new connections between processes like it will on Linux.
+                    options.CreateBoundListenSocket = endpoint =>
+                    {
+                        if (endpoint is not IPEndPoint ip)
+                        {
+                            return SocketTransportOptions.CreateDefaultBoundListenSocket(endpoint);
+                        }
+
+                        // Normally, we'd call CreateDefaultBoundListenSocket for the IPEndpoint too, but we need
+                        // to set ReuseAddress before calling bind, and CreateDefaultBoundListenSocket calls bind.
+                        var listenSocket = new Socket(ip.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
+
+                        // Kestrel expects IPv6Any to bind to both IPv6 and IPv4
+                        if (ip.Address.Equals(IPAddress.IPv6Any))
+                        {
+                            listenSocket.DualMode = true;
+                        }
+
+                        listenSocket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
+                        listenSocket.Bind(ip);
+
+                        return listenSocket;
+                    };
                 }
             });