Special case the uwp sync context 😭 (#2046)

* Special case the uwp sync context 😭

* Attempt #2

* Add changelog

CHANGELOG.md

@@ -1,3 +1,19 @@
+## 5.1.2 (TBD)
+------------------
+
+### Enhancements
+* None
+
+### Fixed
+* Fixed an issue that would result in `Realm accessed from incorrect thread` exception being thrown when accessing a Realm instance on the main thread in UWP apps. (Issue [#2045](https://github.com/realm/realm-dotnet/issues/2045))
+
+### Compatibility
+* Realm Object Server: 3.23.1 or later.
+* Realm Studio: 5.0.0 or later.
+
+### Internal
+* Using Sync 5.0.28 and Core 6.1.3.
+
 ## 5.1.1 (2020-10-02)
 ------------------
 

Realm/Realm/Native/SynchronizationContextScheduler.cs

@@ -49,6 +49,8 @@ internal static class SynchronizationContextScheduler
 
         private class Scheduler
         {
+            private readonly int _threadId;
+
             private volatile bool _isReleased;
             private SynchronizationContext _context;
 
@@ -57,6 +59,7 @@ internal Scheduler(SynchronizationContext context)
                 Argument.NotNull(context, nameof(context));
 
                 _context = context;
+                _threadId = Environment.CurrentManagedThreadId;
             }
 
             internal void Post(IntPtr function_ptr)
@@ -70,7 +73,7 @@ internal void Post(IntPtr function_ptr)
                 }, null);
             }
 
-            internal bool IsOnContext(Scheduler other) => _context.IsSameAs(other?._context ?? SynchronizationContext.Current);
+            internal bool IsOnContext(Scheduler other) => _context == (other?._context ?? SynchronizationContext.Current) || _threadId == (other?._threadId ?? Environment.CurrentManagedThreadId);
 
             [MethodImpl(MethodImplOptions.AggressiveInlining)]
             internal void Invalidate()