Clean up native resources on Unity application exit

CHANGELOG.md

@@ -1,7 +1,9 @@
 ## vNext (TBD)
 
 ### Fixed
-* \[Unity] Fixed an issue where failing to weave an assembly due to modeling errors, would only show an error in the logs once and then fail opening a Realm with `No RealmObjects. Has linker stripped them?`. Now, the weaving errors will show up on every code change/weave attempt and the runtime error will explicitly suggest manually re-running the weaver. (Issue [#2310](https://github.com/realm/realm-dotnet/issues/2310))
+* \[Unity\] Fixed an issue where failing to weave an assembly due to modeling errors, would only show an error in the logs once and then fail opening a Realm with `No RealmObjects. Has linker stripped them?`. Now, the weaving errors will show up on every code change/weave attempt and the runtime error will explicitly suggest manually re-running the weaver. (Issue [#2310](https://github.com/realm/realm-dotnet/issues/2310))
+* \[Unity\] Fixed an issue that would cause the app to hang on exit when using Sync. (PR [#2467](https://github.com/realm/realm-dotnet/pull/2467))
+* \[Unity\] Fixed an issue that would cause the Unity editor on macOS to hang after assembly reload if the app uses Sync. (Issue [#2482](https://github.com/realm/realm-dotnet/issues/2482))
 
 ### Enhancements
 * None

Realm/Realm.UnityUtils/Initializer.cs

@@ -26,12 +26,17 @@ internal static class Initializer
     {
         private static int _isInitialized;
 
+        [Preserve]
         public static void Initialize()
         {
             if (Interlocked.CompareExchange(ref _isInitialized, 1, 0) == 0)
             {
                 InteropConfig.AddPotentialStorageFolder(FileHelper.GetStorageFolder());
                 Logger.Default = new UnityLogger();
+                UnityEngine.Application.quitting += () =>
+                {
+                    NativeCommon.CleanupNativeResources("Application is exiting");
+                };
             }
         }
     }

Realm/Realm/Handles/AppHandle.cs

@@ -31,6 +31,8 @@ namespace Realms.Sync
 {
     internal partial class AppHandle : RealmHandle
     {
+        private static readonly List<WeakReference> _appHandles = new List<WeakReference>();
+
         private static class NativeMethods
         {
 #pragma warning disable IDE1006 // Naming Styles
@@ -196,6 +198,12 @@ public static void Initialize()
         internal AppHandle(IntPtr handle) : base(null, handle)
         {
             EmailPassword = new EmailPasswordApi(this);
+
+            lock (_appHandles)
+            {
+                _appHandles.RemoveAll(a => !a.IsAlive);
+                _appHandles.Add(new WeakReference(this));
+            }
         }
 
         public static AppHandle CreateApp(Native.AppConfiguration config, byte[] encryptionKey)
@@ -205,6 +213,20 @@ public static AppHandle CreateApp(Native.AppConfiguration config, byte[] encrypt
             return new AppHandle(handle);
         }
 
+        public static void ForceCloseHandles()
+        {
+            lock (_appHandles)
+            {
+                foreach (var weakHandle in _appHandles)
+                {
+                    var appHandle = (AppHandle)weakHandle.Target;
+                    appHandle?.Close();
+                }
+
+                _appHandles.Clear();
+            }
+        }
+
         public string GetRealmPath(User user, string partition)
         {
             return MarshalHelpers.GetString((IntPtr buffer, IntPtr bufferLength, out bool isNull, out NativeException ex) =>

Realm/Realm/Handles/SharedRealmHandle.cs

@@ -272,7 +272,7 @@ public static void DeleteFiles(string path)
             nativeException.ThrowIfNecessary();
         }
 
-        public static void CloseAllRealms()
+        public static void ForceCloseNativeRealms()
         {
             NativeMethods.close_all_realms(out var nativeException);
             nativeException.ThrowIfNecessary();

Realm/Realm/InteropConfig.cs

@@ -18,10 +18,8 @@
 
 using System;
 using System.Collections.Generic;
-using System.Diagnostics;
 using System.IO;
 using System.Reflection;
-using Realms.Logging;
 
 namespace Realms
 {
@@ -90,22 +88,7 @@ static InteropConfig()
 
             AppDomain.CurrentDomain.DomainUnload += (_, __) =>
             {
-                Logger.LogDefault(LogLevel.Info, "Realm: Domain is unloading, force closing all Realm instances.");
-
-                try
-                {
-                    var sw = new Stopwatch();
-                    sw.Start();
-
-                    SharedRealmHandle.CloseAllRealms();
-
-                    sw.Stop();
-                    Logger.LogDefault(LogLevel.Info, $"Realm: Closed all native instances in {sw.ElapsedMilliseconds} ms.");
-                }
-                catch (Exception ex)
-                {
-                    Logger.LogDefault(LogLevel.Error, $"Realm: Failed to close all native instances. You may need to restart your app. Error: {ex}");
-                }
+                NativeCommon.CleanupNativeResources("AppDomain is unloading");
             };
         }
 

Realm/Realm/Native/NativeCommon.cs

@@ -18,10 +18,12 @@
 
 // file NativeCommon.cs provides mappings to common functions that don't fit the Table classes etc.
 using System;
+using System.Diagnostics;
 using System.IO;
 using System.Reflection;
 using System.Runtime.InteropServices;
 using System.Threading;
+using Realms.Logging;
 using Realms.Native;
 using Realms.Sync;
 
@@ -60,6 +62,33 @@ internal static void Initialize()
             }
         }
 
+        /// <summary>
+        /// **WARNING**: This will close all native Realm instances and AppHandles. This method is extremely unsafe
+        /// to call in any circumstance where the user might be accessing anything Realm-related. The only places
+        /// where we do call it is in DomainUnload and Application.quitting on Unity. We expect that at this point
+        /// the Application/Domain is being torn down and the user should not be interracting with Realm.
+        /// </summary>
+        public static void CleanupNativeResources(string reason)
+        {
+            try
+            {
+                Logger.LogDefault(LogLevel.Info, $"Realm: Force closing all native instances: {reason}");
+
+                var sw = new Stopwatch();
+                sw.Start();
+
+                AppHandle.ForceCloseHandles();
+                SharedRealmHandle.ForceCloseNativeRealms();
+
+                sw.Stop();
+                Logger.LogDefault(LogLevel.Info, $"Realm: Closed all native instances in {sw.ElapsedMilliseconds} ms.");
+            }
+            catch (Exception ex)
+            {
+                Logger.LogDefault(LogLevel.Error, $"Realm: Failed to close all native instances. You may need to restart your app. Error: {ex}");
+            }
+        }
+
         private static void AddWindowsWrappersToPath(string relativePath, bool isUnityTarget = false)
         {
             try