Cocoa QPA: Delete singletons on exit

This involves QCocoaApplicationDelegate and QCocoaMenuLoader.

The former has been modernized to use blocks. The latter was
not being deleted previously.

Change-Id: Ic4cbfed2d9598fa04130675b3330d985b9489a21
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

src/plugins/platforms/cocoa/qcocoaapplicationdelegate.mm

@@ -86,17 +86,22 @@
 
 QT_USE_NAMESPACE
 
-QT_BEGIN_NAMESPACE
-static QCocoaApplicationDelegate *sharedCocoaApplicationDelegate = nil;
-
-static void cleanupCocoaApplicationDelegate()
-{
-    [sharedCocoaApplicationDelegate release];
-}
-QT_END_NAMESPACE
-
 @implementation QCocoaApplicationDelegate
 
++ (instancetype)sharedDelegate
+{
+    static QCocoaApplicationDelegate *shared = nil;
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{
+        shared = [[self alloc] init];
+        atexit_b(^{
+            [shared release];
+            shared = nil;
+        });
+    });
+    return shared;
+}
+
 - (id)init
 {
     self = [super init];
@@ -120,7 +125,6 @@ QT_END_NAMESPACE
 
 - (void)dealloc
 {
-    sharedCocoaApplicationDelegate = nil;
     [dockMenu release];
     if (reflectionDelegate) {
         [[NSApplication sharedApplication] setDelegate:reflectionDelegate];
@@ -131,27 +135,6 @@ QT_END_NAMESPACE
     [super dealloc];
 }
 
-+ (id)allocWithZone:(NSZone *)zone
-{
-    @synchronized(self) {
-        if (sharedCocoaApplicationDelegate == nil) {
-            sharedCocoaApplicationDelegate = [super allocWithZone:zone];
-            qAddPostRoutine(cleanupCocoaApplicationDelegate);
-            return sharedCocoaApplicationDelegate;
-        }
-    }
-    return nil;
-}
-
-+ (QCocoaApplicationDelegate *)sharedDelegate
-{
-    @synchronized(self) {
-        if (sharedCocoaApplicationDelegate == nil)
-            [[self alloc] init];
-    }
-    return [[sharedCocoaApplicationDelegate retain] autorelease];
-}
-
 - (void)setDockMenu:(NSMenu*)newMenu
 {
     [newMenu retain];

src/plugins/platforms/cocoa/qcocoamenuloader.mm

@@ -57,6 +57,10 @@
     static dispatch_once_t onceToken;
     dispatch_once(&onceToken, ^{
         shared = [[self alloc] init];
+        atexit_b(^{
+            [shared release];
+            shared = nil;
+        });
     });
     return shared;
 }