cocoa: Change the new sync_dispatch hint to async_dispatch.

This is so the default is safer.

include/SDL_hints.h

@@ -981,13 +981,19 @@ extern "C" {
  *  \brief   A variable controlling whether dispatching OpenGL context updates should block the dispatching thread until the main thread finishes processing
  *
  *  This variable can be set to the following values:
- *    "0"       - Dispatching OpenGL context updates will allow the dispatching thread to continue execution.
- *    "1"       - Dispatching OpenGL context updates will block the dispatching thread until the main thread finishes processing.
+ *    "0"       - Dispatching OpenGL context updates will block the dispatching thread until the main thread finishes processing (default).
+ *    "1"       - Dispatching OpenGL context updates will allow the dispatching thread to continue execution.
  *
- *  This hint only applies to Mac OS X
+ *  Generally you want the default, but if you have OpenGL code in a background thread on a Mac, and the main thread
+ *  hangs because it's waiting for that background thread, but that background thread is also hanging because it's
+ *  waiting for the main thread to do an update, this might fix your issue.
+ *
+ *  This hint only applies to macOS.
+ *
+ *  This hint is available since SDL 2.24.0.
  *
  */
-#define SDL_HINT_MAC_OPENGL_SYNC_DISPATCH "SDL_MAC_OPENGL_SYNC_DISPATCH"
+#define SDL_HINT_MAC_OPENGL_ASYNC_DISPATCH "SDL_MAC_OPENGL_ASYNC_DISPATCH"
 
 /**
  *  \brief  A variable setting the double click radius, in pixels.

src/video/cocoa/SDL_cocoaopengl.m

@@ -44,12 +44,12 @@
 #pragma clang diagnostic ignored "-Wdeprecated-declarations"
 #endif
 
-static SDL_bool SDL_opengl_sync_dispatch = SDL_FALSE;
+static SDL_bool SDL_opengl_async_dispatch = SDL_FALSE;
 
 static void SDLCALL
-SDL_OpenGLSyncDispatchChanged(void *userdata, const char *name, const char *oldValue, const char *hint)
+SDL_OpenGLAsyncDispatchChanged(void *userdata, const char *name, const char *oldValue, const char *hint)
 {
-    SDL_opengl_sync_dispatch = SDL_GetStringBoolean(hint, SDL_FALSE);
+    SDL_opengl_async_dispatch = SDL_GetStringBoolean(hint, SDL_FALSE);
 }
 
 @implementation SDLOpenGLContext : NSOpenGLContext
@@ -63,7 +63,7 @@ SDL_OpenGLSyncDispatchChanged(void *userdata, const char *name, const char *oldV
         self->window = NULL;
     }
 
-    SDL_AddHintCallback(SDL_HINT_MAC_OPENGL_SYNC_DISPATCH, SDL_OpenGLSyncDispatchChanged, NULL);
+    SDL_AddHintCallback(SDL_HINT_MAC_OPENGL_ASYNC_DISPATCH, SDL_OpenGLAsyncDispatchChanged, NULL);
     return self;
 }
 
@@ -147,17 +147,17 @@ SDL_OpenGLSyncDispatchChanged(void *userdata, const char *name, const char *oldV
     if ([NSThread isMainThread]) {
         [super update];
     } else {
-        if (SDL_opengl_sync_dispatch) {
-            dispatch_sync(dispatch_get_main_queue(), ^{ [super update]; });
-        } else {
+        if (SDL_opengl_async_dispatch) {
             dispatch_async(dispatch_get_main_queue(), ^{ [super update]; });
+        } else {
+            dispatch_sync(dispatch_get_main_queue(), ^{ [super update]; });
         }
     }
 }
 
 - (void)dealloc
 {
-    SDL_DelHintCallback(SDL_HINT_MAC_OPENGL_SYNC_DISPATCH, SDL_OpenGLSyncDispatchChanged, NULL);
+    SDL_DelHintCallback(SDL_HINT_MAC_OPENGL_ASYNC_DISPATCH, SDL_OpenGLAsyncDispatchChanged, NULL);
 }
 
 @end