Allow RCTDisplayLink to pause more often

Summary:
By default we run the the JS display link, even if there are no modules listening. Given that most listeners will be lazily constructed, let's make it paused by default.

Since RCTTiming almost never unpauses due to some long-lived timers, implement a sleep timer that pauses the displaylink but uses an NSTimer to wake up in time.

Reviewed By: mhorowitz

Differential Revision: D3235044

fbshipit-source-id: 4a340fea552ada1bd8bc0d83b596a7df6f992387

React/Base/RCTDisplayLink.m

@@ -18,6 +18,10 @@
 #import "RCTModuleData.h"
 #import "RCTProfile.h"
 
+#define RCTAssertRunLoop() \
+  RCTAssert(_runLoop == [NSRunLoop currentRunLoop], \
+  @"This method must be called on the CADisplayLink run loop")
+
 @implementation RCTDisplayLink
 {
   CADisplayLink *_jsDisplayLink;
@@ -38,12 +42,13 @@
 - (void)registerModuleForFrameUpdates:(id<RCTBridgeModule>)module
                        withModuleData:(RCTModuleData *)moduleData
 {
-  if ([_frameUpdateObservers containsObject:moduleData] ||
-      ![moduleData.moduleClass conformsToProtocol:@protocol(RCTFrameUpdateObserver)]) {
+  if (![moduleData.moduleClass conformsToProtocol:@protocol(RCTFrameUpdateObserver)] ||
+      [_frameUpdateObservers containsObject:moduleData]) {
     return;
   }
 
   [_frameUpdateObservers addObject:moduleData];
+
   // Don't access the module instance via moduleData, as this will cause deadlock
   id<RCTFrameUpdateObserver> observer = (id<RCTFrameUpdateObserver>)module;
   __weak typeof(self) weakSelf = self;
@@ -54,16 +59,28 @@
     }
 
     CFRunLoopRef cfRunLoop = [strongSelf->_runLoop getCFRunLoop];
-
-    if (!self->_runLoop) {
+    if (!cfRunLoop) {
       return;
     }
 
-    CFRunLoopPerformBlock(cfRunLoop, kCFRunLoopDefaultMode, ^{
-                            [weakSelf updateJSDisplayLinkState];
-                          });
-    CFRunLoopWakeUp(cfRunLoop);
+    if ([NSRunLoop currentRunLoop] == strongSelf->_runLoop) {
+      [weakSelf updateJSDisplayLinkState];
+    } else {
+      CFRunLoopPerformBlock(cfRunLoop, kCFRunLoopDefaultMode, ^{
+        [weakSelf updateJSDisplayLinkState];
+      });
+      CFRunLoopWakeUp(cfRunLoop);
+    }
   };
+
+  // Assuming we're paused right now, we only need to update the display link's state
+  // when the new observer is not paused. If it not paused, the observer will immediately
+  // start receiving updates anyway.
+  if (![observer isPaused] && _runLoop) {
+    CFRunLoopPerformBlock([_runLoop getCFRunLoop], kCFRunLoopDefaultMode, ^{
+      [self updateJSDisplayLinkState];
+    });
+  }
 }
 
 - (void)addToRunLoop:(NSRunLoop *)runLoop
@@ -77,12 +94,6 @@
   [_jsDisplayLink invalidate];
 }
 
-- (void)assertOnRunLoop
-{
-  RCTAssert(_runLoop == [NSRunLoop currentRunLoop],
-            @"This method must be called on the CADisplayLink run loop");
-}
-
 - (void)dispatchBlock:(dispatch_block_t)block
                 queue:(dispatch_queue_t)queue
 {
@@ -95,7 +106,7 @@
 
 - (void)_jsThreadUpdate:(CADisplayLink *)displayLink
 {
-  [self assertOnRunLoop];
+  RCTAssertRunLoop();
 
   RCT_PROFILE_BEGIN_EVENT(RCTProfileTagAlways, @"-[RCTDisplayLink _jsThreadUpdate:]", nil);
 
@@ -121,7 +132,7 @@
 
 - (void)updateJSDisplayLinkState
 {
-  [self assertOnRunLoop];
+  RCTAssertRunLoop();
 
   BOOL pauseDisplayLink = YES;
   for (RCTModuleData *moduleData in _frameUpdateObservers) {
@@ -131,6 +142,7 @@
       break;
     }
   }
+
   _jsDisplayLink.paused = pauseDisplayLink;
 }
 

React/Base/RCTModuleMethod.m

@@ -426,7 +426,7 @@ SEL RCTParseMethodSignature(NSString *methodSignature, NSArray<RCTMethodArgument
 
 - (NSDictionary *)profileArgs
 {
-  if (_profileArgs) {
+  if (!_profileArgs) {
     // This sets _selector
     [self processMethodSignature];
     _profileArgs = @{