[ReactNative] Use a single DisplayLink held by the bridge

React/Base/RCTBridge.h

@@ -10,6 +10,7 @@
 #import <UIKit/UIKit.h>
 
 #import "RCTBridgeModule.h"
+#import "RCTFrameUpdate.h"
 #import "RCTInvalidating.h"
 #import "RCTJavaScriptExecutor.h"
 
@@ -122,4 +123,14 @@ static const char *__rct_import_##module##_##method##__ = #module"."#method;
  */
 - (void)reload;
 
+/**
+ * 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
+ */
+- (void)removeFrameUpdateObserver:(id<RCTFrameUpdateObserver>)observer;
+
 @end

React/Base/RCTBridge.m

@@ -677,6 +677,73 @@ static NSDictionary *RCTLocalModulesConfig()
   return localModules;
 }
 
+@interface RCTDisplayLink : NSObject <RCTInvalidating>
+
+- (instancetype)initWithBridge:(RCTBridge *)bridge NS_DESIGNATED_INITIALIZER;
+
+@end
+
+@interface RCTBridge (RCTDisplayLink)
+
+- (void)_update:(CADisplayLink *)displayLink;
+
+@end
+
+@implementation RCTDisplayLink
+{
+  __weak RCTBridge *_bridge;
+  CADisplayLink *_displayLink;
+}
+
+- (instancetype)initWithBridge:(RCTBridge *)bridge
+{
+  if ((self = [super init])) {
+    _bridge = bridge;
+    _displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(_update:)];
+    [_displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
+  }
+  return self;
+}
+
+- (BOOL)isValid
+{
+  return _displayLink != nil;
+}
+
+- (void)invalidate
+{
+  if (self.isValid) {
+    [_displayLink invalidate];
+    _displayLink = nil;
+  }
+}
+
+- (void)_update:(CADisplayLink *)displayLink
+{
+  [_bridge _update:displayLink];
+}
+
+@end
+
+@interface RCTFrameUpdate (Private)
+
+- (instancetype)initWithDisplayLink:(CADisplayLink *)displayLink;
+
+@end
+
+@implementation RCTFrameUpdate
+
+- (instancetype)initWithDisplayLink:(CADisplayLink *)displayLink
+{
+  if ((self = [super init])) {
+    _timestamp = displayLink.timestamp;
+    _deltaTime = displayLink.duration;
+  }
+  return self;
+}
+
+@end
+
 @implementation RCTBridge
 {
   RCTSparseArray *_modulesByID;
@@ -685,6 +752,8 @@ static NSDictionary *RCTLocalModulesConfig()
   Class _executorClass;
   NSURL *_bundleURL;
   RCTBridgeModuleProviderBlock _moduleProvider;
+  RCTDisplayLink *_displayLink;
+  NSMutableSet *_frameUpdateObservers;
   BOOL _loading;
 }
 
@@ -711,6 +780,8 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
   _latestJSExecutor = _javaScriptExecutor;
   _eventDispatcher = [[RCTEventDispatcher alloc] initWithBridge:self];
   _shadowQueue = dispatch_queue_create("com.facebook.React.ShadowQueue", DISPATCH_QUEUE_SERIAL);
+  _displayLink = [[RCTDisplayLink alloc] initWithBridge:self];
+  _frameUpdateObservers = [[NSMutableSet alloc] init];
 
   // Register passed-in module instances
   NSMutableDictionary *preregisteredModules = [[NSMutableDictionary alloc] init];
@@ -891,6 +962,9 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
   [_javaScriptExecutor invalidate];
   _javaScriptExecutor = nil;
 
+  [_displayLink invalidate];
+  _frameUpdateObservers = nil;
+
   // Invalidate modules
   for (id target in _modulesByID.allObjects) {
     if ([target respondsToSelector:@selector(invalidate)]) {
@@ -1075,6 +1149,26 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
   return YES;
 }
 
+- (void)_update:(CADisplayLink *)displayLink
+{
+  RCTFrameUpdate *frameUpdate = [[RCTFrameUpdate alloc] initWithDisplayLink:displayLink];
+  for (id<RCTFrameUpdateObserver> observer in _frameUpdateObservers) {
+    if (![observer respondsToSelector:@selector(isPaused)] || ![observer isPaused]) {
+      [observer didUpdateFrame:frameUpdate];
+    }
+  }
+}
+
+- (void)addFrameUpdateObserver:(id<RCTFrameUpdateObserver>)observer
+{
+  [_frameUpdateObservers addObject:observer];
+}
+
+- (void)removeFrameUpdateObserver:(id<RCTFrameUpdateObserver>)observer
+{
+  [_frameUpdateObservers removeObject:observer];
+}
+
 - (void)reload
 {
   if (!_loading) {

React/Base/RCTFrameUpdate.h

@@ -0,0 +1,44 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+/**
+ * Interface containing the information about the last screen refresh.
+ */
+@interface RCTFrameUpdate : NSObject
+
+/**
+ * Timestamp for the actual screen refresh
+ */
+@property (nonatomic, readonly) NSTimeInterval timestamp;
+
+/**
+ * Time since the last frame update ( >= 16.6ms )
+ */
+@property (nonatomic, readonly) NSTimeInterval deltaTime;
+
+@end
+
+/**
+ * Protocol that must be implemented for subscribing to display refreshes (DisplayLink updates)
+ */
+@protocol RCTFrameUpdateObserver <NSObject>
+
+/**
+ * Method called on every screen refresh (if paused != YES)
+ */
+- (void)didUpdateFrame:(RCTFrameUpdate *)update;
+
+@optional
+
+/**
+ * Synthesize and set to true to pause the calls to -[didUpdateFrame:]
+ */
+@property (nonatomic, assign, getter=isPaused) BOOL paused;
+
+@end