[Java.Interop] Avoid double-disposing PeerReferences

src/Java.Interop/Java.Interop/JniRuntime.JniValueManager.cs

@@ -143,6 +143,13 @@ public virtual void DisposePeer (IJavaPeerable value)
 				if (value == null)
 					throw new ArgumentNullException (nameof (value));
 
+				if (!value.PeerReference.IsValid)
+					return;
+
+				RemovePeer (value);
+
+				value.Disposed ();
+
 				var h = value.PeerReference;
 				if (!h.IsValid)
 					return;
@@ -155,8 +162,6 @@ void DisposePeer (JniObjectReference h, IJavaPeerable value)
 				if (disposed)
 					throw new ObjectDisposedException (GetType ().Name);
 
-				value.Disposed ();
-				RemovePeer (value);
 				var o = Runtime.ObjectReferenceManager;
 				if (o.LogGlobalReferenceMessages) {
 					o.WriteGlobalReferenceLine ("Disposing PeerReference={0} IdentityHashCode=0x{1} Instance=0x{2} Instance.Type={3} Java.Type={4}",

tests/Java.Interop-Tests/Java.Interop/JavaObjectTest.cs

@@ -185,6 +185,14 @@ public void CrossThreadSharingRequresRegistration ()
 			o.ToString ();
 			o.Dispose ();
 		}
+
+		[Test]
+		public void NestedDisposeInvocations ()
+		{
+			var value = new MyDisposableObject ();
+			value.Dispose ();
+			value.Dispose ();
+		}
 	}
 
 	class JavaObjectWithNoJavaPeer : JavaObject {
@@ -215,5 +223,25 @@ protected override void Dispose (bool disposing)
 				OnFinalized ();
 		}
 	}
+
+	[JniTypeSignature ("java/lang/Object")]
+	class MyDisposableObject : JavaObject {
+		bool _isDisposed;
+
+		public MyDisposableObject ()
+		{
+		}
+
+		protected override void Dispose (bool disposing)
+		{
+			if (_isDisposed) {
+				return;
+			}
+			_isDisposed = true;
+			if (this.PeerReference.IsValid)
+				this.Dispose ();
+			base.Dispose (disposing);
+		}
+	}
 }