Merge pull request #12099 from jtattermusch/csharp_shutdownevent

Add GrpcEnvironment.ShuttingDown event

src/csharp/Grpc.Core.Tests/GrpcEnvironmentTest.cs

@@ -18,6 +18,7 @@
 
 using System;
 using System.Linq;
+using System.Threading;
 using Grpc.Core;
 using NUnit.Framework;
 
@@ -75,5 +76,19 @@ namespace Grpc.Core.Tests
             var parts = coreVersion.Split('.');
             Assert.AreEqual(3, parts.Length);
         }
+
+        [Test]
+        public void ShuttingDownEventIsFired()
+        {
+            var cts = new CancellationTokenSource();
+            var handler = new EventHandler((sender, args) => { cts.Cancel(); });
+            
+            GrpcEnvironment.ShuttingDown += handler;
+            var env = GrpcEnvironment.AddRef();
+            GrpcEnvironment.ReleaseAsync().Wait();
+            GrpcEnvironment.ShuttingDown -= handler;
+            
+            Assert.IsTrue(cts.Token.IsCancellationRequested);
+        }
     }
 }

src/csharp/Grpc.Core/GrpcEnvironment.cs

@@ -49,7 +49,7 @@ namespace Grpc.Core
         readonly DebugStats debugStats = new DebugStats();
         readonly AtomicCounter cqPickerCounter = new AtomicCounter();
 
-        bool isClosed;
+        bool isShutdown;
 
         /// <summary>
         /// Returns a reference-counted instance of initialized gRPC environment.
@@ -237,6 +237,12 @@ namespace Grpc.Core
             }
         }
 
+        /// <summary>
+        /// Occurs when <c>GrpcEnvironment</c> is about the start the shutdown logic.
+        /// If <c>GrpcEnvironment</c> is later initialized and shutdown, the event will be fired again (unless unregistered first).
+        /// </summary>
+        public static event EventHandler ShuttingDown;
+
         /// <summary>
         /// Creates gRPC environment.
         /// </summary>
@@ -311,13 +317,16 @@ namespace Grpc.Core
         /// </summary>
         private async Task ShutdownAsync()
         {
-            if (isClosed)
+            if (isShutdown)
             {
-                throw new InvalidOperationException("Close has already been called");
+                throw new InvalidOperationException("ShutdownAsync has already been called");
             }
+
+            await Task.Run(() => ShuttingDown?.Invoke(this, null)).ConfigureAwait(false);
+
             await threadPool.StopAsync().ConfigureAwait(false);
             GrpcNativeShutdown();
-            isClosed = true;
+            isShutdown = true;
 
             debugStats.CheckOK();
         }