add shutdownhook for CoreCLR

src/csharp/Grpc.Core/GrpcEnvironment.cs

@@ -352,11 +352,11 @@ namespace Grpc.Core
                 {
                     if (!hooksRegistered)
                     {
-                        // TODO(jtattermusch): register shutdownhooks for CoreCLR as well
-#if !NETSTANDARD1_5
-
-                        AppDomain.CurrentDomain.ProcessExit += ShutdownHookHandler;
-                        AppDomain.CurrentDomain.DomainUnload += ShutdownHookHandler;
+#if NETSTANDARD1_5
+                        System.Runtime.Loader.AssemblyLoadContext.Default.Unloading += (assemblyLoadContext) => { HandleShutdown(); };
+#else
+                        AppDomain.CurrentDomain.ProcessExit += (sender, eventArgs) => { HandleShutdown(); };
+                        AppDomain.CurrentDomain.DomainUnload += (sender, eventArgs) => { HandleShutdown(); };
 #endif
                     }
                     hooksRegistered = true;
@@ -364,9 +364,9 @@ namespace Grpc.Core
             }
 
             /// <summary>
-            /// Handler for AppDomain.DomainUnload and AppDomain.ProcessExit hooks.
+            /// Handler for AppDomain.DomainUnload, AppDomain.ProcessExit and AssemblyLoadContext.Unloading hooks.
             /// </summary>
-            private static void ShutdownHookHandler(object sender, EventArgs e)
+            private static void HandleShutdown()
             {
                 Task.WaitAll(GrpcEnvironment.ShutdownChannelsAsync(), GrpcEnvironment.KillServersAsync());
             }

src/csharp/Grpc.Core/project.json

@@ -38,6 +38,7 @@
     "netstandard1.5": {
       "dependencies": {
         "NETStandard.Library": "1.6.0",
+        "System.Runtime.Loader": "4.0.0",
         "System.Threading.Thread": "4.0.0"
       }
     }

templates/src/csharp/Grpc.Core/project.json.template

@@ -40,6 +40,7 @@
       "netstandard1.5": {
         "dependencies": {
           "NETStandard.Library": "1.6.0",
+          "System.Runtime.Loader": "4.0.0",
           "System.Threading.Thread": "4.0.0"
         }
       }