Pause JS DisplayLink if nothing to process.

Reviewed By: @jspahrsummers

Differential Revision: D2489107

React/Base/RCTBatchedBridge.m

@@ -309,6 +309,15 @@ RCT_EXTERN NSArray *RCTGetModuleClasses(void);
     config[moduleData.name] = moduleData.config;
     if ([moduleData.instance conformsToProtocol:@protocol(RCTFrameUpdateObserver)]) {
       [_frameUpdateObservers addObject:moduleData];
+
+      id<RCTFrameUpdateObserver> observer = (id<RCTFrameUpdateObserver>)moduleData.instance;
+      __weak typeof(self) weakSelf = self;
+      __weak typeof(_javaScriptExecutor) weakJavaScriptExecutor = _javaScriptExecutor;
+      observer.pauseCallback = ^{
+        [weakJavaScriptExecutor executeBlockOnJavaScriptQueue:^{
+          [weakSelf updateJSDisplayLinkState];
+        }];
+      };
     }
   }
 
@@ -317,6 +326,23 @@ RCT_EXTERN NSArray *RCTGetModuleClasses(void);
   }, NULL);
 }
 
+- (void)updateJSDisplayLinkState
+{
+  RCTAssertJSThread();
+
+  BOOL pauseDisplayLink = ![_scheduledCallbacks count] && ![_scheduledCalls count];
+  if (pauseDisplayLink) {
+    for (RCTModuleData *moduleData in _frameUpdateObservers) {
+      id<RCTFrameUpdateObserver> observer = (id<RCTFrameUpdateObserver>)moduleData.instance;
+      if (!observer.paused) {
+        pauseDisplayLink = NO;
+        break;
+      }
+    }
+  }
+  _jsDisplayLink.paused = pauseDisplayLink;
+}
+
 - (void)injectJSONConfiguration:(NSString *)configJSON
                      onComplete:(void (^)(NSError *))onComplete
 {
@@ -620,6 +646,7 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithBundleURL:(__unused NSURL *)bundleUR
     } else {
       [strongSelf->_scheduledCalls addObject:call];
     }
+    [strongSelf updateJSDisplayLinkState];
 
     RCTProfileEndEvent(0, @"objc_call", call);
   }];
@@ -804,7 +831,7 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithBundleURL:(__unused NSURL *)bundleUR
   RCTFrameUpdate *frameUpdate = [[RCTFrameUpdate alloc] initWithDisplayLink:displayLink];
   for (RCTModuleData *moduleData in _frameUpdateObservers) {
     id<RCTFrameUpdateObserver> observer = (id<RCTFrameUpdateObserver>)moduleData.instance;
-    if (![observer respondsToSelector:@selector(isPaused)] || !observer.paused) {
+    if (!observer.paused) {
       RCT_IF_DEV(NSString *name = [NSString stringWithFormat:@"[%@ didUpdateFrame:%f]", observer, displayLink.timestamp];)
       RCTProfileBeginFlowEvent();
 
@@ -833,6 +860,7 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithBundleURL:(__unused NSURL *)bundleUR
     [self _actuallyInvokeAndProcessModule:@"BatchedBridge"
                                    method:@"processBatch"
                                 arguments:@[[calls valueForKey:@"js_args"]]];
+    [self updateJSDisplayLinkState];
   }
 
   RCTProfileEndEvent(0, @"objc_call", nil);

React/Base/RCTEventDispatcher.m

@@ -93,18 +93,30 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init)
 
 @synthesize bridge = _bridge;
 @synthesize paused = _paused;
+@synthesize pauseCallback = _pauseCallback;
 
 RCT_EXPORT_MODULE()
 
 - (instancetype)init
 {
   if ((self = [super init])) {
+    _paused = YES;
     _eventQueue = [NSMutableDictionary new];
     _eventQueueLock = [NSLock new];
   }
   return self;
 }
 
+- (void)setPaused:(BOOL)paused
+{
+  if (_paused != paused) {
+    _paused = paused;
+    if (_pauseCallback) {
+      _pauseCallback();
+    }
+  }
+}
+
 - (void)sendAppEventWithName:(NSString *)name body:(id)body
 {
   [_bridge enqueueJSCall:@"RCTNativeAppEventEmitter.emit"
@@ -169,7 +181,7 @@ RCT_EXPORT_MODULE()
   }
 
   _eventQueue[eventID] = event;
-  _paused = NO;
+  self.paused = NO;
 
   [_eventQueueLock unlock];
 }
@@ -202,7 +214,7 @@ RCT_EXPORT_MODULE()
   [_eventQueueLock lock];
    NSDictionary *eventQueue = _eventQueue;
   _eventQueue = [NSMutableDictionary new];
-  _paused = YES;
+  self.paused = YES;
   [_eventQueueLock unlock];
 
   for (id<RCTEvent> event in eventQueue.allValues) {

React/Base/RCTFrameUpdate.h

@@ -40,11 +40,15 @@
  */
 - (void)didUpdateFrame:(RCTFrameUpdate *)update;
 
-@optional
-
 /**
  * Synthesize and set to true to pause the calls to -[didUpdateFrame:]
  */
-@property (nonatomic, assign, getter=isPaused) BOOL paused;
+@property (nonatomic, readonly, getter=isPaused) BOOL paused;
+
+/**
+ * Callback for pause/resume observer.
+ * Observer should call it when paused property is changed.
+ */
+@property (nonatomic, copy) dispatch_block_t pauseCallback;
 
 @end

React/Modules/RCTTiming.m

@@ -71,6 +71,7 @@
 
 @synthesize bridge = _bridge;
 @synthesize paused = _paused;
+@synthesize pauseCallback = _pauseCallback;
 
 RCT_EXPORT_MODULE()
 
@@ -120,7 +121,7 @@ RCT_EXPORT_MODULE()
 
 - (void)stopTimers
 {
-  _paused = YES;
+  self.paused = YES;
 }
 
 - (void)startTimers
@@ -129,7 +130,17 @@ RCT_EXPORT_MODULE()
     return;
   }
 
-  _paused = NO;
+  self.paused = NO;
+}
+
+- (void)setPaused:(BOOL)paused
+{
+  if (_paused != paused) {
+    _paused = paused;
+    if (_pauseCallback) {
+      _pauseCallback();
+    }
+  }
 }
 
 - (void)didUpdateFrame:(__unused RCTFrameUpdate *)update

React/Views/RCTNavigator.m

@@ -269,6 +269,7 @@ NSInteger kNeverProgressed = -10000;
 }
 
 @synthesize paused = _paused;
+@synthesize pauseCallback = _pauseCallback;
 
 - (instancetype)initWithBridge:(RCTBridge *)bridge
 {
@@ -321,6 +322,16 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithCoder:(NSCoder *)aDecoder)
   }
 }
 
+- (void)setPaused:(BOOL)paused
+{
+  if (_paused != paused) {
+    _paused = paused;
+    if (_pauseCallback) {
+      _pauseCallback();
+    }
+  }
+}
+
 - (void)dealloc
 {
   _navigationController.delegate = nil;
@@ -355,14 +366,14 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithCoder:(NSCoder *)aDecoder)
     _dummyView.frame = (CGRect){{destination, 0}, CGSizeZero};
     _currentlyTransitioningFrom = indexOfFrom;
     _currentlyTransitioningTo = indexOfTo;
-    _paused = NO;
+    self.paused = NO;
   }
   completion:^(__unused id<UIViewControllerTransitionCoordinatorContext> context) {
     [weakSelf freeLock];
     _currentlyTransitioningFrom = 0;
     _currentlyTransitioningTo = 0;
     _dummyView.frame = CGRectZero;
-    _paused = YES;
+    self.paused = YES;
     // Reset the parallel position tracker
   }];
 }