NSView lifetime fixes (#104)

* drain autorelease pools in Window::open_* methods

* fixes to NSView lifetime logic:

- in open_parented and open_blocking, release NSView after adding
  it as a subview of the parent
- in open_blocking, don't call autorelease on NSWindow. previously
  it was a no-op, but now that we are actually draining our
  autorelease pools, it ends up prematurely releasing the window.

* fixes to NSView cleanup logic:

- Move retainCount check to before calling [super release].
  If [super release] happens first, then in the final call to
  release, [super release] deallocates the object and the call to
  retainCount results in a segfault.

- Move objc_disposeClassPair to dealloc. Previously we were
  calling it when retainCount == 1, but that's exactly when
  dealloc is called, so this is cleaner. Also, we need to call
  objc_disposeClassPair after [super dealloc].

NOTE: The circular-reference-breaking logic in release is
definitely broken. It's easy to thwart it by e.g. creating a
wgpu surface at some point after build() or dropping one at some
point before drop(). Need to come up with a better solution.

Author: micahrj

src/macos/view.rs

@@ -119,6 +119,10 @@ unsafe fn create_view_class() -> &'static Class {
         sel!(release),
         release as extern "C" fn(&mut Object, Sel)
     );
+    class.add_method(
+        sel!(dealloc),
+        dealloc as extern "C" fn(&mut Object, Sel)
+    );
     class.add_method(
         sel!(viewWillMoveToWindow:),
         view_will_move_to_window as extern "C" fn(&Object, Sel, id)
@@ -229,11 +233,17 @@ extern "C" fn accepts_first_mouse(
 
 
 extern "C" fn release(this: &mut Object, _sel: Sel) {
-    unsafe {
-        let superclass = msg_send![this, superclass];
-
-        let () = msg_send![super(this, superclass), release];
-    }
+    // Hack for breaking circular references. We store the value of retainCount
+    // after build(), and then when retainCount drops back to that value, we
+    // drop the WindowState, hoping that any circular references it holds back
+    // to the NSView (e.g. wgpu surfaces) get released.
+    //
+    // This is definitely broken, since it can be thwarted by e.g. creating a
+    // wgpu surface at some point after build() (which will mean the NSView
+    // never gets dealloced) or dropping a wgpu surface at some point before
+    // drop() (which will mean the WindowState gets dropped early).
+    //
+    // TODO: Find a better solution for circular references.
 
     unsafe {
         let retain_count: usize = msg_send![this, retainCount];
@@ -257,11 +267,23 @@ extern "C" fn release(this: &mut Object, _sel: Sel) {
             }
         }
 
-        if retain_count == 1 {
-            // Delete class
-            let class = msg_send![this, class];
-            ::objc::runtime::objc_disposeClassPair(class);
-        }
+    }
+
+    unsafe {
+        let superclass = msg_send![this, superclass];
+        let () = msg_send![super(this, superclass), release];
+    }
+}
+
+extern "C" fn dealloc(this: &mut Object, _sel: Sel) {
+    unsafe {
+        let class = msg_send![this, class];
+
+        let superclass = msg_send![this, superclass];
+        let () = msg_send![super(this, superclass), dealloc];
+
+        // Delete class
+        ::objc::runtime::objc_disposeClassPair(class);
     }
 }
 

src/macos/window.rs

@@ -41,7 +41,7 @@ impl Window {
         B: FnOnce(&mut crate::Window) -> H,
         B: Send + 'static,
     {
-        let _pool = unsafe { NSAutoreleasePool::new(nil) };
+        let pool = unsafe { NSAutoreleasePool::new(nil) };
 
         let handle = if let RawWindowHandle::MacOS(handle) = parent.raw_window_handle() {
             handle
@@ -60,6 +60,9 @@ impl Window {
 
         unsafe {
             let _: id = msg_send![handle.ns_view as *mut Object, addSubview: ns_view];
+            let () = msg_send![ns_view as id, release];
+
+            let () = msg_send![pool, drain];
         }
     }
 
@@ -69,7 +72,7 @@ impl Window {
         B: FnOnce(&mut crate::Window) -> H,
         B: Send + 'static,
     {
-        let _pool = unsafe { NSAutoreleasePool::new(nil) };
+        let pool = unsafe { NSAutoreleasePool::new(nil) };
 
         let ns_view = unsafe { create_view(&options) };
 
@@ -82,6 +85,10 @@ impl Window {
 
         Self::init(window, build);
 
+        unsafe {
+            let () = msg_send![pool, drain];
+        }
+
         raw_window_handle
     }
 
@@ -91,7 +98,7 @@ impl Window {
         B: FnOnce(&mut crate::Window) -> H,
         B: Send + 'static,
     {
-        let _pool = unsafe { NSAutoreleasePool::new(nil) };
+        let pool = unsafe { NSAutoreleasePool::new(nil) };
 
         // It seems prudent to run NSApp() here before doing other
         // work. It runs [NSApplication sharedApplication], which is
@@ -131,8 +138,7 @@ impl Window {
                     NSWindowStyleMask::NSTitledWindowMask,
                     NSBackingStoreBuffered,
                     NO,
-                )
-                .autorelease();
+                );
             ns_window.center();
 
             let title = NSString::alloc(nil)
@@ -156,9 +162,10 @@ impl Window {
 
         unsafe {
             ns_window.setContentView_(ns_view);
-        }
+            let () = msg_send![ns_view as id, release];
+
+            let () = msg_send![pool, drain];
 
-        unsafe {
             app.run();
         }
     }