From 60b9825f64eb0f2631da848efe7dadacf8c0e873 Mon Sep 17 00:00:00 2001
From: zeromus <zeromus@users.noreply.github.com>
Date: Sat, 15 Jul 2017 22:09:50 -0500
Subject: [PATCH] fix race condition in test of active window from input thread
 (which was a bad idea in the first place) which can throw null references in
 unlucky cases (fixes #917)

---
 BizHawk.Client.EmuHawk/Input/Input.cs | 1 +
 BizHawk.Client.EmuHawk/MainForm.cs    | 6 +++---
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/BizHawk.Client.EmuHawk/Input/Input.cs b/BizHawk.Client.EmuHawk/Input/Input.cs
index 67c88793aa..cc8d2fa6a8 100644
--- a/BizHawk.Client.EmuHawk/Input/Input.cs
+++ b/BizHawk.Client.EmuHawk/Input/Input.cs
@@ -414,6 +414,7 @@ namespace BizHawk.Client.EmuHawk
 
 					}
 
+					//WHAT!? WE SHOULD NOT BE SO NAIVELY TOUCHING MAINFORM FROM THE INPUTTHREAD. ITS BUSY RUNNING.
 					bool swallow = !GlobalWin.MainForm.AllowInput(false);
 
 					foreach (var ie in _NewEvents)
diff --git a/BizHawk.Client.EmuHawk/MainForm.cs b/BizHawk.Client.EmuHawk/MainForm.cs
index eb34dd6e2a..9965c31309 100644
--- a/BizHawk.Client.EmuHawk/MainForm.cs
+++ b/BizHawk.Client.EmuHawk/MainForm.cs
@@ -643,15 +643,15 @@ namespace BizHawk.Client.EmuHawk
 
 			// even more special logic for TAStudio:
 			// TODO - implement by event filter in TAStudio
-			if (ActiveForm is TAStudio)
+			var maybeTAStudio = ActiveForm as TAStudio;
+			if (maybeTAStudio != null)
 			{
 				if (yieldAlt)
 				{
 					return false;
 				}
 
-				var ts = (TAStudio)ActiveForm;
-				if (ts.IsInMenuLoop)
+				if (maybeTAStudio.IsInMenuLoop)
 				{
 					return false;
 				}