macOS: Don't rely on QGuiApplication::instance() during CVDisplayLink callback

The display-link callback comes in on a secondary thread, so there's a possible
race in using QGuiApplication::instance() to check whether or not we're on the
main thread.

Change-Id: Ic26bca8f5f54847a1e1b11dc92e786693c86e9de
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

1 files changed, 1 insertions, 4 deletions

diff --git a/src/plugins/platforms/cocoa/qcocoascreen.mm b/src/plugins/platforms/cocoa/qcocoascreen.mm
index 36c11ba8af..80dd7e40d3 100644
--- a/src/plugins/platforms/cocoa/qcocoascreen.mm
+++ b/src/plugins/platforms/cocoa/qcocoascreen.mm
@@ -269,15 +269,12 @@ struct DeferredDebugHelper
 
 void QCocoaScreen::deliverUpdateRequests()
 {
-    if (!QGuiApplication::instance())
-        return;
-
     // The CVDisplayLink callback is a notification that it's a good time to produce a new frame.
     // Since the callback is delivered on a separate thread we have to marshal it over to the
     // main thread, as Qt requires update requests to be delivered there. This needs to happen
     // asynchronously, as otherwise we may end up deadlocking if the main thread calls back
     // into any of the CVDisplayLink APIs.
-    if (QThread::currentThread() != QGuiApplication::instance()->thread()) {
+    if (!NSThread.isMainThread) {
         // We're explicitly not using the data of the GCD source to track the pending updates,
         // as the data isn't reset to 0 until after the event handler, and also doesn't update
         // during the event handler, both of which we need to track late frames.