Merge pull request #16308 from jtattermusch/csharp_ios_crash_workaround

C#: avoid shutdown crash on iOS

src/csharp/Grpc.Core/GrpcEnvironment.cs

@@ -50,6 +50,7 @@ namespace Grpc.Core
         static int requestCallContextPoolThreadLocalCapacity = DefaultRequestCallContextPoolThreadLocalCapacity;
         static readonly HashSet<Channel> registeredChannels = new HashSet<Channel>();
         static readonly HashSet<Server> registeredServers = new HashSet<Server>();
+        static readonly AtomicCounter nativeInitCounter = new AtomicCounter();
 
         static ILogger logger = new LogLevelFilterLogger(new ConsoleLogger(), LogLevel.Off, true);
 
@@ -360,12 +361,25 @@ namespace Grpc.Core
 
         internal static void GrpcNativeInit()
         {
+            if (!IsNativeShutdownAllowed && nativeInitCounter.Count > 0)
+            {
+                // Normally grpc_init and grpc_shutdown calls should come in pairs (C core does reference counting),
+                // but in case we avoid grpc_shutdown calls altogether, calling grpc_init has no effect
+                // besides incrementing an internal C core counter that could theoretically overflow.
+                // To avoid this theoretical possibility we guard repeated calls to grpc_init()
+                // with a 64-bit atomic counter (that can't realistically overflow).
+                return;
+            }
             NativeMethods.Get().grpcsharp_init();
+            nativeInitCounter.Increment();
         }
 
         internal static void GrpcNativeShutdown()
         {
-            NativeMethods.Get().grpcsharp_shutdown();
+            if (IsNativeShutdownAllowed)
+            {
+                NativeMethods.Get().grpcsharp_shutdown();
+            }
         }
 
         /// <summary>
@@ -411,6 +425,14 @@ namespace Grpc.Core
             return GetThreadPoolSizeOrDefault();
         }
 
+        // On some platforms (specifically iOS), thread local variables in native code
+        // require initialization/destruction. By skipping the grpc_shutdown() call,
+        // we avoid a potential crash where grpc_shutdown() has already destroyed
+        // the thread local variables, but some C core's *_destroy() methods still
+        // need to run (e.g. they may be run by finalizer thread which is out of our control)
+        // For more context, see https://github.com/grpc/grpc/issues/16294
+        private static bool IsNativeShutdownAllowed => !PlatformApis.IsXamarinIOS && !PlatformApis.IsUnityIOS;
+
         private static class ShutdownHooks
         {
             static object staticLock = new object();

src/csharp/Grpc.Core/Internal/PlatformApis.cs

@@ -42,6 +42,7 @@ namespace Grpc.Core.Internal
         static readonly bool isMono;
         static readonly bool isNetCore;
         static readonly bool isUnity;
+        static readonly bool isUnityIOS;
         static readonly bool isXamarin;
         static readonly bool isXamarinIOS;
         static readonly bool isXamarinAndroid;
@@ -63,7 +64,25 @@ namespace Grpc.Core.Internal
             isNetCore = false;
 #endif
             isMono = Type.GetType("Mono.Runtime") != null;
-            isUnity = Type.GetType(UnityEngineApplicationClassName) != null;
+
+            // Unity
+            var unityApplicationClass = Type.GetType(UnityEngineApplicationClassName);
+            if (unityApplicationClass != null)
+            {
+                isUnity = true;
+                // Consult value of Application.platform via reflection
+                // https://docs.unity3d.com/ScriptReference/Application-platform.html
+                var platformProperty = unityApplicationClass.GetTypeInfo().GetProperty("platform");
+                var unityRuntimePlatform = platformProperty?.GetValue(null)?.ToString();
+                isUnityIOS = (unityRuntimePlatform == "IPhonePlayer");
+            }
+            else
+            {
+                isUnity = false;
+                isUnityIOS = false;
+            }
+
+            // Xamarin
             isXamarinIOS = Type.GetType(XamarinIOSObjectClassName) != null;
             isXamarinAndroid = Type.GetType(XamarinAndroidObjectClassName) != null;
             isXamarin = isXamarinIOS || isXamarinAndroid;
@@ -97,6 +116,14 @@ namespace Grpc.Core.Internal
             get { return isUnity; }
         }
 
+        /// <summary>
+        /// true if running on Unity iOS, false otherwise.
+        /// </summary>
+        public static bool IsUnityIOS
+        {
+            get { return isUnityIOS; }
+        }
+
         /// <summary>
         /// true if running on a Xamarin platform (either Xamarin.Android or Xamarin.iOS),
         /// false otherwise.