diff --git a/Libraries/RCTWebSocketDebugger/RCTWebSocketExecutor.m b/Libraries/RCTWebSocketDebugger/RCTWebSocketExecutor.m
index eb6428fc2..753c8d76d 100644
--- a/Libraries/RCTWebSocketDebugger/RCTWebSocketExecutor.m
+++ b/Libraries/RCTWebSocketDebugger/RCTWebSocketExecutor.m
@@ -175,6 +175,11 @@ typedef void (^WSMessageCallback)(NSError *error, NSDictionary *reply);
   });
 }
 
+- (void)executeBlockOnJavaScriptQueue:(dispatch_block_t)block
+{
+  dispatch_async(dispatch_get_main_queue(), block);
+}
+
 - (void)invalidate
 {
   _socket.delegate = nil;
diff --git a/React/Base/RCTBridge.m b/React/Base/RCTBridge.m
index 1c676640e..a4a4362b0 100644
--- a/React/Base/RCTBridge.m
+++ b/React/Base/RCTBridge.m
@@ -694,7 +694,7 @@ static NSDictionary *RCTLocalModulesConfig()
 
 @interface RCTDisplayLink : NSObject <RCTInvalidating>
 
-- (instancetype)initWithBridge:(RCTBridge *)bridge NS_DESIGNATED_INITIALIZER;
+- (instancetype)initWithBridge:(RCTBridge *)bridge selector:(SEL)selector NS_DESIGNATED_INITIALIZER;
 
 @end
 
@@ -708,14 +708,16 @@ static NSDictionary *RCTLocalModulesConfig()
 {
   __weak RCTBridge *_bridge;
   CADisplayLink *_displayLink;
+  SEL _selector;
 }
 
-- (instancetype)initWithBridge:(RCTBridge *)bridge
+- (instancetype)initWithBridge:(RCTBridge *)bridge selector:(SEL)selector
 {
   if ((self = [super init])) {
     _bridge = bridge;
+    _selector = selector;
     _displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(_update:)];
-    [_displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
+    [_displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
   }
   return self;
 }
@@ -735,7 +737,10 @@ static NSDictionary *RCTLocalModulesConfig()
 
 - (void)_update:(CADisplayLink *)displayLink
 {
-  [_bridge _update:displayLink];
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
+  [_bridge performSelector:_selector withObject:displayLink];
+#pragma clang diagnostic pop
 }
 
 @end
@@ -770,6 +775,7 @@ static NSDictionary *RCTLocalModulesConfig()
   NSURL *_bundleURL;
   RCTBridgeModuleProviderBlock _moduleProvider;
   RCTDisplayLink *_displayLink;
+  RCTDisplayLink *_vsyncDisplayLink;
   NSMutableSet *_frameUpdateObservers;
   NSMutableArray *_scheduledCalls;
   RCTSparseArray *_scheduledCallbacks;
@@ -799,11 +805,15 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
   _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];
   _scheduledCallbacks = [[RCTSparseArray alloc] init];
 
+  [_javaScriptExecutor executeBlockOnJavaScriptQueue:^{
+    _displayLink = [[RCTDisplayLink alloc] initWithBridge:self selector:@selector(_jsThreadUpdate:)];
+  }];
+  _vsyncDisplayLink = [[RCTDisplayLink alloc] initWithBridge:self selector:@selector(_mainThreadUpdate:)];
+
   // Register passed-in module instances
   NSMutableDictionary *preregisteredModules = [[NSMutableDictionary alloc] init];
   for (id<RCTBridgeModule> module in _moduleProvider ? _moduleProvider() : nil) {
@@ -1008,6 +1018,7 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
   _javaScriptExecutor = nil;
 
   [_displayLink invalidate];
+  [_vsyncDisplayLink invalidate];
   _frameUpdateObservers = nil;
 
   // Invalidate modules
@@ -1294,9 +1305,9 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
   return YES;
 }
 
-- (void)_update:(CADisplayLink *)displayLink
+- (void)_jsThreadUpdate:(CADisplayLink *)displayLink
 {
-  RCTProfileImmediateEvent(@"VSYNC", displayLink.timestamp, @"g");
+  RCTProfileImmediateEvent(@"JS Thread Tick", displayLink.timestamp, @"g");
   RCTProfileBeginEvent();
 
   RCTFrameUpdate *frameUpdate = [[RCTFrameUpdate alloc] initWithDisplayLink:displayLink];
@@ -1306,13 +1317,6 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
     }
   }
 
-  [self _runScheduledCalls];
-
-  RCTProfileEndEvent(@"DispatchFrameUpdate", @"objc_call", nil);
-}
-
-- (void)_runScheduledCalls
-{
 #if BATCHED_BRIDGE
 
   NSArray *calls = [_scheduledCallbacks.allObjects arrayByAddingObjectsFromArray:_scheduledCalls];
@@ -1330,6 +1334,13 @@ static id<RCTJavaScriptExecutor> _latestJSExecutor;
   }
 
 #endif
+
+  RCTProfileEndEvent(@"DispatchFrameUpdate", @"objc_call", nil);
+}
+
+- (void)_mainThreadUpdate:(CADisplayLink *)displayLink
+{
+  RCTProfileImmediateEvent(@"VSYNC", displayLink.timestamp, @"g");
 }
 
 - (void)addFrameUpdateObserver:(id<RCTFrameUpdateObserver>)observer
diff --git a/React/Base/RCTJavaScriptExecutor.h b/React/Base/RCTJavaScriptExecutor.h
index 8ff5a1658..eb7fd7d31 100644
--- a/React/Base/RCTJavaScriptExecutor.h
+++ b/React/Base/RCTJavaScriptExecutor.h
@@ -42,6 +42,13 @@ typedef void (^RCTJavaScriptCallback)(id json, NSError *error);
 - (void)injectJSONText:(NSString *)script
    asGlobalObjectNamed:(NSString *)objectName
               callback:(RCTJavaScriptCompleteBlock)onComplete;
+
+/**
+ * Enqueue a block to run in the executors JS thread. Fallback to `dispatch_async`
+ * on the main queue if the executor doesn't own a thread.
+ */
+- (void)executeBlockOnJavaScriptQueue:(dispatch_block_t)block;
+
 @end
 
 static const char *RCTJavaScriptExecutorID = "RCTJavaScriptExecutorID";
diff --git a/React/Base/RCTProfile.m b/React/Base/RCTProfile.m
index 929a026a9..19c6900c7 100644
--- a/React/Base/RCTProfile.m
+++ b/React/Base/RCTProfile.m
@@ -36,6 +36,7 @@ NSDictionary *RCTProfileInfo;
 NSUInteger RCTProfileEventID = 0;
 NSMutableDictionary *RCTProfileOngoingEvents;
 NSTimeInterval RCTProfileStartTime;
+NSLock *_RCTProfileLock;
 
 #pragma mark - Macros
 
@@ -51,6 +52,11 @@ if (!RCTProfileIsProfiling()) { \
   return __VA_ARGS__; \
 }
 
+#define RCTProfileLock(...) \
+[_RCTProfileLock lock]; \
+__VA_ARGS__ \
+[_RCTProfileLock unlock]
+
 #pragma mark - Private Helpers
 
 NSNumber *RCTProfileTimestamp(NSTimeInterval timestamp)
@@ -66,7 +72,6 @@ NSString *RCTProfileMemory(vm_size_t memory)
 
 NSDictionary *RCTProfileGetMemoryUsage(void)
 {
-  CHECK(@{});
   struct task_basic_info info;
   mach_msg_type_number_t size = sizeof(info);
   kern_return_t kerr = task_info(mach_task_self(),
@@ -88,66 +93,81 @@ NSDictionary *RCTProfileGetMemoryUsage(void)
 
 BOOL RCTProfileIsProfiling(void)
 {
-  return RCTProfileInfo != nil;
+  RCTProfileLock(
+    BOOL profiling = RCTProfileInfo != nil;
+  );
+  return profiling;
 }
 
 void RCTProfileInit(void)
 {
-  RCTProfileStartTime = CACurrentMediaTime();
-  RCTProfileOngoingEvents = [[NSMutableDictionary alloc] init];
-  RCTProfileInfo = @{
-    RCTProfileTraceEvents: [[NSMutableArray alloc] init],
-    RCTProfileSamples: [[NSMutableArray alloc] init],
-  };
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    _RCTProfileLock = [[NSLock alloc] init];
+  });
+  RCTProfileLock(
+    RCTProfileStartTime = CACurrentMediaTime();
+    RCTProfileOngoingEvents = [[NSMutableDictionary alloc] init];
+    RCTProfileInfo = @{
+      RCTProfileTraceEvents: [[NSMutableArray alloc] init],
+      RCTProfileSamples: [[NSMutableArray alloc] init],
+    };
+  );
 }
 
 NSString *RCTProfileEnd(void)
 {
-  NSString *log = RCTJSONStringify(RCTProfileInfo, NULL);
-  RCTProfileEventID = 0;
-  RCTProfileInfo = nil;
-  RCTProfileOngoingEvents = nil;
+  RCTProfileLock(
+    NSString *log = RCTJSONStringify(RCTProfileInfo, NULL);
+    RCTProfileEventID = 0;
+    RCTProfileInfo = nil;
+    RCTProfileOngoingEvents = nil;
+  );
   return log;
 }
 
 NSNumber *_RCTProfileBeginEvent(void)
 {
   CHECK(@0);
-  NSNumber *eventID = @(++RCTProfileEventID);
-  RCTProfileOngoingEvents[eventID] = RCTProfileTimestamp(CACurrentMediaTime());
+  RCTProfileLock(
+    NSNumber *eventID = @(++RCTProfileEventID);
+    RCTProfileOngoingEvents[eventID] = RCTProfileTimestamp(CACurrentMediaTime());
+  );
   return eventID;
 }
 
 void _RCTProfileEndEvent(NSNumber *eventID, NSString *name, NSString *categories, id args)
 {
   CHECK();
-  NSNumber *startTimestamp = RCTProfileOngoingEvents[eventID];
-  if (!startTimestamp) {
-    return;
-  }
+  RCTProfileLock(
+    NSNumber *startTimestamp = RCTProfileOngoingEvents[eventID];
+    if (startTimestamp) {
+      NSNumber *endTimestamp = RCTProfileTimestamp(CACurrentMediaTime());
 
-  NSNumber *endTimestamp = RCTProfileTimestamp(CACurrentMediaTime());
-
-  RCTProfileAddEvent(RCTProfileTraceEvents,
-    @"name": name,
-    @"cat": categories,
-    @"ph": @"X",
-    @"ts": startTimestamp,
-    @"dur": @(endTimestamp.doubleValue - startTimestamp.doubleValue),
-    @"args": args ?: @[],
+      RCTProfileAddEvent(RCTProfileTraceEvents,
+        @"name": name,
+        @"cat": categories,
+        @"ph": @"X",
+        @"ts": startTimestamp,
+        @"dur": @(endTimestamp.doubleValue - startTimestamp.doubleValue),
+        @"args": args ?: @[],
+      );
+      [RCTProfileOngoingEvents removeObjectForKey:eventID];
+    }
   );
-  [RCTProfileOngoingEvents removeObjectForKey:eventID];
 }
 
 void RCTProfileImmediateEvent(NSString *name, NSTimeInterval timestamp, NSString *scope)
 {
   CHECK();
-  RCTProfileAddEvent(RCTProfileTraceEvents,
-    @"name": name,
-    @"ts": RCTProfileTimestamp(timestamp),
-    @"scope": scope,
-    @"ph": @"i",
-    @"args": RCTProfileGetMemoryUsage(),
+  RCTProfileLock(
+    RCTProfileAddEvent(RCTProfileTraceEvents,
+      @"name": name,
+      @"ts": RCTProfileTimestamp(timestamp),
+      @"scope": scope,
+      @"ph": @"i",
+      @"args": RCTProfileGetMemoryUsage(),
+    );
   );
 }
 
diff --git a/React/Modules/RCTTiming.m b/React/Modules/RCTTiming.m
index 62d42a7bb..1d99c1a2d 100644
--- a/React/Modules/RCTTiming.m
+++ b/React/Modules/RCTTiming.m
@@ -142,8 +142,6 @@ RCT_IMPORT_METHOD(RCTJSTimers, callTimers)
 
 - (void)didUpdateFrame:(RCTFrameUpdate *)update
 {
-  RCTAssertMainThread();
-
   NSMutableArray *timersToCall = [[NSMutableArray alloc] init];
   for (RCTTimer *timer in _timers.allObjects) {
     if ([timer updateFoundNeedsJSUpdate]) {