macOS: Clarify what static mutex in QCocoaGLContext is used for

Change-Id: I4af0b78dbecad40b2a73cdbdb09a8eb60efdb013
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 6 insertions, 4 deletions

diff --git a/src/plugins/platforms/cocoa/qcocoaglcontext.mm b/src/plugins/platforms/cocoa/qcocoaglcontext.mm
index f11016679a..069429796e 100644
--- a/src/plugins/platforms/cocoa/qcocoaglcontext.mm
+++ b/src/plugins/platforms/cocoa/qcocoaglcontext.mm
@@ -393,8 +393,10 @@ bool QCocoaGLContext::setDrawable(QPlatformSurface *surface)
     return true;
 }
 
-// NSOpenGLContext is not re-entrant (https://openradar.appspot.com/37064579)
-static QMutex s_contextMutex;
+// NSOpenGLContext is not re-entrant. Even when using separate contexts per thread,
+// view, and window, calls into the API will still deadlock. For more information
+// see https://openradar.appspot.com/37064579
+static QMutex s_reentrancyMutex;
 
 void QCocoaGLContext::update()
 {
@@ -403,7 +405,7 @@ void QCocoaGLContext::update()
     // render-loop that doesn't return to one of the outer pools.
     QMacAutoReleasePool pool;
 
-    QMutexLocker locker(&s_contextMutex);
+    QMutexLocker locker(&s_reentrancyMutex);
     qCInfo(lcQpaOpenGLContext) << "Updating" << m_context << "for" << m_context.view;
     [m_context update];
 }
@@ -422,7 +424,7 @@ void QCocoaGLContext::swapBuffers(QPlatformSurface *surface)
         return;
     }
 
-    QMutexLocker locker(&s_contextMutex);
+    QMutexLocker locker(&s_reentrancyMutex);
     [m_context flushBuffer];
 }