Changed default method queue to a background queue.

Libraries/ActionSheetIOS/RCTActionSheetManager.m

@@ -30,6 +30,11 @@ RCT_EXPORT_MODULE()
   return self;
 }
 
+- (dispatch_queue_t)methodQueue
+{
+  return dispatch_get_main_queue();
+}
+
 RCT_EXPORT_METHOD(showActionSheetWithOptions:(NSDictionary *)options
                   failureCallback:(RCTResponseSenderBlock)failureCallback
                   successCallback:(RCTResponseSenderBlock)successCallback)

Libraries/Geolocation/RCTLocationObserver.m

@@ -128,6 +128,11 @@ RCT_EXPORT_MODULE()
   _locationManager.delegate = nil;
 }
 
+- (dispatch_queue_t)methodQueue
+{
+  return dispatch_get_main_queue();
+}
+
 #pragma mark - Private API
 
 - (void)beginLocationUpdates

Libraries/LinkingIOS/RCTLinkingManager.m

@@ -36,6 +36,11 @@ RCT_EXPORT_MODULE()
   [[NSNotificationCenter defaultCenter] removeObserver:self];
 }
 
+- (dispatch_queue_t)methodQueue
+{
+  return dispatch_queue_create("com.facebook.React.LinkingManager", DISPATCH_QUEUE_SERIAL);
+}
+
 + (BOOL)application:(UIApplication *)application
             openURL:(NSURL *)URL
   sourceApplication:(NSString *)sourceApplication
@@ -56,16 +61,16 @@ RCT_EXPORT_MODULE()
 
 RCT_EXPORT_METHOD(openURL:(NSURL *)URL)
 {
+  // Doesn't really matter what thread we call this on since it exits the app
   [[UIApplication sharedApplication] openURL:URL];
 }
 
 RCT_EXPORT_METHOD(canOpenURL:(NSURL *)URL
                   callback:(RCTResponseSenderBlock)callback)
 {
-  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
-    BOOL canOpen = [[UIApplication sharedApplication] canOpenURL:URL];
-    callback(@[@(canOpen)]);
-  });
+  // This can be expensive, so we deliberately don't call on main thread
+  BOOL canOpen = [[UIApplication sharedApplication] canOpenURL:URL];
+  callback(@[@(canOpen)]);
 }
 
 - (NSDictionary *)constantsToExport

React/Base/RCTBridge.h

@@ -62,9 +62,9 @@ extern NSString *RCTBridgeModuleNameForClass(Class bridgeModuleClass);
 /**
  * This method is used to call functions in the JavaScript application context.
  * It is primarily intended for use by modules that require two-way communication
- * with the JavaScript code. Method should be regsitered using the
+ * with the JavaScript code. Method should be registered using the
  * RCT_IMPORT_METHOD macro below. Attempting to call a method that has not been
- * registered will result in an error.
+ * registered will result in an error. Safe to call from any thread.
  */
 - (void)enqueueJSCall:(NSString *)moduleDotMethod args:(NSArray *)args;
 
@@ -112,17 +112,17 @@ static const char *__rct_import_##module##_##method##__ = #module"."#method;
 @property (nonatomic, readonly, getter=isLoading) BOOL loading;
 
 /**
- * Reload the bundle and reset executor and modules.
+ * Reload the bundle and reset executor & modules. Safe to call from any thread.
  */
 - (void)reload;
 
 /**
- * Add a new observer that will be called on every screen refresh
+ * Add a new observer that will be called on every screen refresh.
  */
 - (void)addFrameUpdateObserver:(id<RCTFrameUpdateObserver>)observer;
 
 /**
- * Stop receiving screen refresh updates for the given observer
+ * Stop receiving screen refresh updates for the given observer.
  */
 - (void)removeFrameUpdateObserver:(id<RCTFrameUpdateObserver>)observer;
 

React/Base/RCTBridge.m

@@ -228,6 +228,7 @@ static NSArray *RCTBridgeModuleClassesByModuleID(void)
   NSMethodSignature *_methodSignature;
   NSArray *_argumentBlocks;
   NSString *_methodName;
+  dispatch_block_t _methodQueue;
 }
 
 static Class _globalExecutorClass;
@@ -762,6 +763,7 @@ static NSDictionary *RCTLocalModulesConfig()
 {
   RCTSparseArray *_modulesByID;
   RCTSparseArray *_queuesByID;
+  dispatch_queue_t _methodQueue;
   NSDictionary *_modulesByName;
   id<RCTJavaScriptExecutor> _javaScriptExecutor;
   Class _executorClass;
@@ -787,7 +789,6 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
     [self setUp];
     [self bindKeys];
   }
-
   return self;
 }
 
@@ -797,6 +798,7 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
   _javaScriptExecutor = RCTCreateExecutor(executorClass);
   _latestJSExecutor = _javaScriptExecutor;
   _eventDispatcher = [[RCTEventDispatcher alloc] initWithBridge:self];
+  _methodQueue = dispatch_queue_create("com.facebook.React.BridgeMethodQueue", DISPATCH_QUEUE_SERIAL);
   _displayLink = [[RCTDisplayLink alloc] initWithBridge:self];
   _frameUpdateObservers = [[NSMutableSet alloc] init];
   _scheduledCalls = [[NSMutableArray alloc] init];
@@ -850,11 +852,14 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
     }
   }
 
-  // Get method queue
+  // Get method queues
   _queuesByID = [[RCTSparseArray alloc] init];
   [_modulesByID enumerateObjectsUsingBlock:^(id<RCTBridgeModule> module, NSNumber *moduleID, BOOL *stop) {
     if ([module respondsToSelector:@selector(methodQueue)]) {
-      _queuesByID[moduleID] = [module methodQueue] ?: dispatch_get_main_queue();
+      dispatch_queue_t queue = [module methodQueue];
+      if (queue) {
+        _queuesByID[moduleID] = queue;
+      }
     }
   }];
 
@@ -895,11 +900,6 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
       } else {
         [[NSNotificationCenter defaultCenter] postNotificationName:RCTJavaScriptDidLoadNotification
                                                             object:self];
-
-        [[NSNotificationCenter defaultCenter] addObserver:self
-                                                 selector:@selector(reload)
-                                                     name:RCTReloadNotification
-                                                   object:nil];
       }
       [[NSNotificationCenter defaultCenter] addObserver:self
                                                selector:@selector(reload)
@@ -1205,7 +1205,7 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
   [_modulesByID enumerateObjectsUsingBlock:^(id<RCTBridgeModule> module, NSNumber *moduleID, BOOL *stop) {
     if ([module respondsToSelector:@selector(batchDidComplete)]) {
       dispatch_queue_t queue = _queuesByID[moduleID];
-      dispatch_async(queue ?: dispatch_get_main_queue(), ^{
+      dispatch_async(queue ?: _methodQueue, ^{
         [module batchDidComplete];
       });
     }
@@ -1240,7 +1240,7 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
 
   __weak RCTBridge *weakSelf = self;
   dispatch_queue_t queue = _queuesByID[moduleID];
-  dispatch_async(queue ?: dispatch_get_main_queue(), ^{
+  dispatch_async(queue ?: _methodQueue, ^{
     RCTProfileBeginEvent();
     __strong RCTBridge *strongSelf = weakSelf;
 
@@ -1320,13 +1320,15 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
 
 - (void)reload
 {
-  if (!_loading) {
-    // If the bridge has not loaded yet, the context will be already invalid at
-    // the time the javascript gets executed.
-    // It will crash the javascript, and even the next `load` won't render.
-    [self invalidate];
-    [self setUp];
-  }
+  dispatch_async(dispatch_get_main_queue(), ^{
+    if (!_loading) {
+      // If the bridge has not loaded yet, the context will be already invalid at
+      // the time the javascript gets executed.
+      // It will crash the javascript, and even the next `load` won't render.
+      [self invalidate];
+      [self setUp];
+    }
+  });
 }
 
 + (void)logMessage:(NSString *)message level:(NSString *)level

React/Base/RCTBridgeModule.h

@@ -91,18 +91,32 @@ typedef void (^RCTResponseSenderBlock)(NSArray *response);
 
 /**
  * The queue that will be used to call all exported methods. If omitted, this
- * will default the main queue, which is recommended for any methods that
- * interact with UIKit. If your methods perform heavy work such as filesystem
- * or network access, you should return a custom serial queue. Example:
+ * will call on the default background queue, which is avoids blocking the main
+ * thread.
+ *
+ * If the methods in your module need to interact with UIKit methods, they will
+ * probably need to call those on the main thread, as most of UIKit is main-
+ * thread-only. You can tell React Native to call your module methods on the
+ * main thread by returning a reference to the main queue, like this:
+ *
+ * - (dispatch_queue_t)methodQueue
+ * {
+ *   return dispatch_get_main_queue();
+ * }
+ *
+ * If your methods perform heavy work such as synchronous filesystem or network
+ * access, you probably don't want to block the default background queue, as
+ * this will stall other methods. Instead, you should return a custom serial
+ * queue, like this:
  *
  * - (dispatch_queue_t)methodQueue
  * {
  *   return dispatch_queue_create("com.mydomain.FileQueue", DISPATCH_QUEUE_SERIAL);
  * }
  *
- * Alternatively, if only some methods on the module should be executed on a
- * background queue you can leave this method unimplemented, and simply
- * dispatch_async() within the method itself.
+ * Alternatively, if only some methods of the module should be executed on a
+ * particular queue you can leave this method unimplemented, and simply
+ * dispatch_async() to the required queue within the method itself.
  */
 - (dispatch_queue_t)methodQueue;
 

React/Modules/RCTAlertManager.m

@@ -35,6 +35,11 @@ RCT_EXPORT_MODULE()
   return self;
 }
 
+- (dispatch_queue_t)methodQueue
+{
+  return dispatch_get_main_queue();
+}
+
 /**
  * @param {NSDictionary} args Dictionary of the form
  *

React/Modules/RCTStatusBarManager.m

@@ -26,6 +26,11 @@ static BOOL RCTViewControllerBasedStatusBarAppearance()
 
 RCT_EXPORT_MODULE()
 
+- (dispatch_queue_t)methodQueue
+{
+  return dispatch_get_main_queue();
+}
+
 RCT_EXPORT_METHOD(setStyle:(UIStatusBarStyle)statusBarStyle
                   animated:(BOOL)animated)
 {

React/Modules/RCTTiming.m

@@ -108,6 +108,11 @@ RCT_IMPORT_METHOD(RCTJSTimers, callTimers)
   [[NSNotificationCenter defaultCenter] removeObserver:self];
 }
 
+- (dispatch_queue_t)methodQueue
+{
+  return dispatch_get_main_queue();
+}
+
 - (BOOL)isValid
 {
   return _bridge != nil;