Unblock FlutterResizeSynchronizer on engine shutdown

shell/platform/darwin/macos/framework/Source/FlutterEngine.mm

@@ -489,6 +489,10 @@ - (void)shutDownEngine {
     return;
   }
 
+  if (_viewController && _viewController.flutterView) {
+    [_viewController.flutterView shutdown];
+  }
+
   FlutterEngineResult result = _embedderAPI.Deinitialize(_engine);
   if (result != kSuccess) {
     NSLog(@"Could not de-initialize the Flutter engine: error %d", result);

shell/platform/darwin/macos/framework/Source/FlutterResizeSynchronizer.h

@@ -75,4 +75,9 @@
  */
 - (void)requestCommit;
 
+/**
+ * Called when shutting down. Unblocks everything and prevents any further synchronization.
+ */
+- (void)shutdown;
+
 @end

shell/platform/darwin/macos/framework/Source/FlutterResizeSynchronizer.mm

@@ -34,6 +34,9 @@ @interface FlutterResizeSynchronizer () {
   // Target size for resizing.
   CGSize _newSize;
 
+  // if YES prevents all synchronization
+  BOOL _shuttingDown;
+
   __weak id<FlutterResizeSynchronizerDelegate> _delegate;
 }
 @end
@@ -54,7 +57,7 @@ - (void)beginResize:(CGSize)size notify:(dispatch_block_t)notify {
     return;
   }
 
-  if (!_receivedFirstFrame) {
+  if (!_receivedFirstFrame || _shuttingDown) {
     // No blocking until framework produces at least one frame
     notify();
     return;
@@ -77,7 +80,7 @@ - (void)beginResize:(CGSize)size notify:(dispatch_block_t)notify {
 
   _waiting = YES;
 
-  _condBlockRequestCommit.wait(lock, [&] { return _pendingCommit; });
+  _condBlockRequestCommit.wait(lock, [&] { return _pendingCommit || _shuttingDown; });
 
   [_delegate resizeSynchronizerFlush:self];
   [_delegate resizeSynchronizerCommit:self];
@@ -104,7 +107,7 @@ - (BOOL)shouldEnsureSurfaceForSize:(CGSize)size {
 
 - (void)requestCommit {
   std::unique_lock<std::mutex> lock(_mutex);
-  if (!_acceptingCommit) {
+  if (!_acceptingCommit || _shuttingDown) {
     return;
   }
 
@@ -113,7 +116,7 @@ - (void)requestCommit {
   _pendingCommit = YES;
   if (_waiting) {  // BeginResize is in progress, interrupt it and schedule commit call
     _condBlockRequestCommit.notify_all();
-    _condBlockBeginResize.wait(lock, [&]() { return !_pendingCommit; });
+    _condBlockBeginResize.wait(lock, [&]() { return !_pendingCommit || _shuttingDown; });
   } else {
     // No resize, schedule commit on platform thread and wait until either done
     // or interrupted by incoming BeginResize
@@ -128,8 +131,15 @@ - (void)requestCommit {
         _condBlockBeginResize.notify_all();
       }
     });
-    _condBlockBeginResize.wait(lock, [&]() { return !_pendingCommit; });
+    _condBlockBeginResize.wait(lock, [&]() { return !_pendingCommit || _shuttingDown; });
   }
 }
 
+- (void)shutdown {
+  std::unique_lock<std::mutex> lock(_mutex);
+  _shuttingDown = YES;
+  _condBlockBeginResize.notify_all();
+  _condBlockRequestCommit.notify_all();
+}
+
 @end

shell/platform/darwin/macos/framework/Source/FlutterView.h

@@ -56,4 +56,10 @@
  */
 - (nonnull FlutterRenderBackingStore*)backingStoreForSize:(CGSize)size;
 
+/**
+ * Must be called when shutting down. Unblocks raster thread and prevents any further
+ * synchronization.
+ */
+- (void)shutdown;
+
 @end

shell/platform/darwin/macos/framework/Source/FlutterView.mm

@@ -124,4 +124,8 @@ - (void)viewDidChangeBackingProperties {
   [_reshapeListener viewDidReshape:self];
 }
 
+- (void)shutdown {
+  [_resizeSynchronizer shutdown];
+}
+
 @end