[Darwin] Unstored attributes should be flushed to storage on shutdown

src/darwin/Framework/CHIP/MTRDeviceControllerDataStore.h

@@ -93,6 +93,13 @@ typedef void (^MTRDeviceControllerDataStoreClusterDataHandler)(NSDictionary<NSNu
 - (nullable NSDictionary<NSString *, id> *)getStoredDeviceDataForNodeID:(NSNumber *)nodeID;
 - (void)storeDeviceData:(NSDictionary<NSString *, id> *)data forNodeID:(NSNumber *)nodeID;
 
+/**
+ * Mechanism for API client to perform a block after previous async operations (writes) on the storage queue have executed.
+ *
+ * If no block is passed in, then the method returns after having synchronously flushed the queue.
+ */
+- (void)synchronouslyPerformBlock:(void (^_Nullable)(void))block;
+
 @end
 
 NS_ASSUME_NONNULL_END

src/darwin/Framework/CHIP/MTRDeviceControllerDataStore.mm

@@ -1169,6 +1169,15 @@ - (void)storeDeviceData:(NSDictionary<NSString *, id> *)data forNodeID:(NSNumber
     });
 }
 
+- (void)synchronouslyPerformBlock:(void (^_Nullable)(void))block
+{
+    dispatch_sync(_storageDelegateQueue, ^{
+        if (block) {
+            block();
+        }
+    });
+}
+
 @end
 
 @implementation MTRCASESessionResumptionInfo

src/darwin/Framework/CHIP/MTRDeviceController_Concrete.mm

@@ -449,6 +449,13 @@ - (void)cleanupAfterStartup
     for (MTRDevice * device in devices) {
         [device invalidate];
     }
+
+    // Since MTRDevice invalidate may issue asynchronous writes to storage, perform a
+    // block synchronously on the storage delegate queue to flush those operations.
+    [self.controllerDataStore synchronouslyPerformBlock:^{
+        MTR_LOG("%@ Finished flushing data store", self);
+    }];
+
     [self stopBrowseForCommissionables];
 
     [_factory controllerShuttingDown:self];

src/darwin/Framework/CHIP/MTRDevice_Concrete.mm

@@ -842,6 +842,9 @@ - (void)invalidate
 {
     MTR_LOG("%@ invalidate", self);
 
+    // First flush unstored attributes if any
+    [self _persistClusterData];
+
     [_asyncWorkQueue invalidate];
 
     os_unfair_lock_lock(&self->_timeSyncLock);