From 05d483bc5b00f7d7fa29baccb6993fc29289fce8 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sat, 2 Mar 2019 23:17:31 -0500
Subject: [PATCH] Corrects potential machine shutdown race condition.

---
 .../Documents/MachineDocument.swift           | 30 +++++++++----------
 1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift b/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift
index c337449f8..733701706 100644
--- a/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift	
+++ b/OSBindings/Mac/Clock Signal/Documents/MachineDocument.swift	
@@ -199,23 +199,23 @@ class MachineDocument:
 
 	// MARK: CSOpenGLViewDelegate
 	final func openGLViewRedraw(_ view: CSOpenGLView, event redrawEvent: CSOpenGLViewRedrawEvent) {
-		if let machine = self.machine {
-			switch redrawEvent {
-				case .timer:
-					bestEffortLock.lock()
-					if let bestEffortUpdater = bestEffortUpdater {
-						bestEffortLock.unlock()
-						bestEffortUpdater.update()
-					} else {
-						bestEffortLock.unlock()
-					}
-					machine.updateView(forPixelSize: view.backingSize)
-					fallthrough
-
-				case .appKit:
-					machine.drawView(forPixelSize: view.backingSize)
+		if redrawEvent == .timer {
+			bestEffortLock.lock()
+			if let bestEffortUpdater = bestEffortUpdater {
+				bestEffortLock.unlock()
+				bestEffortUpdater.update()
+			} else {
+				bestEffortLock.unlock()
 			}
 		}
+
+		if drawLock.try() {
+			if redrawEvent == .timer {
+				machine.updateView(forPixelSize: view.backingSize)
+			}
+			machine.drawView(forPixelSize: view.backingSize)
+			drawLock.unlock()
+		}
 	}
 
 	// MARK: Runtime media insertion.