Re-introduce SIGTERM signal handling

According to the .NET 6/8 docs, this is handled on Windows as well

OpenSim/Region/Application/OpenSim.cs

@@ -38,6 +38,7 @@ using System.Text;
 using System.Text.RegularExpressions;
 using System.Timers;
 using System.Net;
+using System.Runtime.InteropServices;
 using log4net;
 using NDesk.Options;
 using Nini.Config;
@@ -79,6 +80,7 @@ namespace OpenSim
         private string m_timedScript = "disabled";
         private int m_timeInterval = 1200;
         private System.Timers.Timer m_scriptTimer;
+        private PosixSignalRegistration m_signalReg;
 
         public OpenSim(IConfigSource configSource) : base(configSource)
         {
@@ -132,6 +134,12 @@ namespace OpenSim
             m_log.Info("[OPENSIM MAIN]: Using async_call_method " + Util.FireAndForgetMethod);
 
             m_log.InfoFormat("[OPENSIM MAIN] Running GC in {0} mode", GCSettings.IsServerGC ? "server":"workstation");
+
+            m_signalReg = PosixSignalRegistration.Create(PosixSignal.SIGTERM, context =>
+                    {
+                        m_log.Info("Received SIGTERM, shutting down");
+                        MainConsole.Instance.RunCommand("shutdown");
+                    });
         }
 
         /// <summary>
@@ -1520,5 +1528,7 @@ namespace OpenSim
             result = result.TrimEnd(' ');
             return result;
         }
+
     }
+
 }

OpenSim/Server/ServerMain.cs

@@ -32,6 +32,7 @@ using System;
 using System.IO;
 using System.Net;
 using System.Net.Security;
+using System.Runtime.InteropServices;
 using System.Security.Cryptography.X509Certificates;
 using System.Collections.Generic;
 using OpenSim.Framework;
@@ -50,6 +51,7 @@ namespace OpenSim.Server
         protected static List<IServiceConnector> m_ServiceConnectors = new();
 
         protected static PluginLoader loader;
+        private static PosixSignalRegistration m_signalReg;
         private static bool m_NoVerifyCertChain = false;
         private static bool m_NoVerifyCertHostname = false;
 
@@ -95,13 +97,20 @@ namespace OpenSim.Server
             Culture.SetCurrentCulture();
             Culture.SetDefaultCurrentCulture();
 
+            m_signalReg = PosixSignalRegistration.Create(PosixSignal.SIGTERM, context =>
+                    {
+                        m_log.Info("Received SIGTERM, shutting down");
+                        m_Server?.Shutdown();
+                        Util.StopThreadPool();
+                    });
+
             ServicePointManager.DefaultConnectionLimit = 64;
             ServicePointManager.MaxServicePointIdleTime = 30000;
 
             ServicePointManager.Expect100Continue = false;
             ServicePointManager.UseNagleAlgorithm = false;
             ServicePointManager.ServerCertificateValidationCallback = ValidateServerCertificate;
-           
+
             m_Server = new HttpServerBase("R.O.B.U.S.T.", args);
 
             string registryLocation;