[ReactNative] Add RCTAssertThread and restrict -[UIManager addUIBlock:] to _shadowQueue

Summary:
@public

Add `RCTAssertThread` to `RCTAssert.h` for convenience when checking the current/queue,
it accepts either a `NSString *`, `NSThread *` or `dispatch_queue_t` as the object to be checked

Also add a check to `-[RCTUIManager addUIBlock:]` - There was a discussion on github (https://github.com/facebook/react-native/issues/1365)
due to the weird behavior caused by calling it from a different thread/queue (it might be added after `batchDidComplete` has been called
and will just be dispatched on the next call from JS to objc)

Test Plan:
Change `-[RCTAnimationExperimentalManager methodQueue]` to return `dispatch_get_main_queue()` and run the 2048 example,
it should dispatch with a helpful message (screenshot on the comments)

React/Base/RCTAssert.h

@@ -62,3 +62,31 @@ RCT_EXTERN RCTAssertFunction RCTGetAssertFunction(void);
  * assert info to an extra service without changing the default behavior.
  */
 RCT_EXTERN void RCTAddAssertFunction(RCTAssertFunction assertFunction);
+
+/**
+ * Get the current thread's name (or the current queue, if in debug mode)
+ */
+RCT_EXTERN NSString *RCTCurrentThreadName(void);
+
+/**
+ * Convenience macro to assert which thread is currently running (DEBUG mode only)
+ */
+#if DEBUG
+
+#define RCTAssertThread(thread, format...) \
+_Pragma("clang diagnostic push") \
+_Pragma("clang diagnostic ignored \"-Wdeprecated-declarations\"") \
+RCTAssert( \
+  [(id)thread isKindOfClass:[NSString class]] ? \
+    [RCTCurrentThreadName() isEqualToString:(NSString *)thread] : \
+    [(id)thread isKindOfClass:[NSThread class]] ? \
+      [NSThread currentThread] ==  (NSThread *)thread : \
+      dispatch_get_current_queue() == (dispatch_queue_t)thread, \
+  format); \
+_Pragma("clang diagnostic pop")
+
+#else
+
+#define RCTAssertThread(thread, format...)
+
+#endif

React/Base/RCTAssert.m

@@ -60,3 +60,20 @@ void RCTAddAssertFunction(RCTAssertFunction assertFunction)
     RCTCurrentAssertFunction = assertFunction;
   }
 }
+
+NSString *RCTCurrentThreadName(void)
+{
+  NSThread *thread = [NSThread currentThread];
+  NSString *threadName = [thread isMainThread] ? @"main" : thread.name;
+  if (threadName.length == 0) {
+#if DEBUG // This is DEBUG not RCT_DEBUG because it *really* must not ship in RC
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
+    threadName = @(dispatch_queue_get_label(dispatch_get_current_queue()));
+#pragma clang diagnostic pop
+#else
+    threadName = [NSString stringWithFormat:@"%p", thread];
+#endif
+  }
+  return threadName;
+}

React/Base/RCTLog.h

@@ -42,18 +42,12 @@ typedef void (^RCTLogFunction)(
   NSString *message
 );
 
-/**
- * Get a given thread's name (or the current queue, if in debug mode)
- */
-RCT_EXTERN NSString *RCTThreadName(NSThread *);
-
 /**
  * A method to generate a string from a collection of log data. To omit any
  * particular data from the log, just pass nil or zero for the argument.
  */
 RCT_EXTERN NSString *RCTFormatLog(
   NSDate *timestamp,
-  NSThread *thread,
   RCTLogLevel level,
   NSString *fileName,
   NSNumber *lineNumber,

React/Base/RCTLog.m

@@ -53,7 +53,7 @@ RCTLogFunction RCTDefaultLogFunction = ^(
 )
 {
   NSString *log = RCTFormatLog(
-    [NSDate date], [NSThread currentThread], level, fileName, lineNumber, message
+    [NSDate date], level, fileName, lineNumber, message
   );
   fprintf(stderr, "%s\n", log.UTF8String);
   fflush(stderr);
@@ -99,25 +99,8 @@ void RCTPerformBlockWithLogPrefix(void (^block)(void), NSString *prefix)
   [prefixStack removeLastObject];
 }
 
-NSString *RCTThreadName(NSThread *thread)
-{
-  NSString *threadName = [thread isMainThread] ? @"main" : thread.name;
-  if (threadName.length == 0) {
-#if DEBUG // This is DEBUG not RCT_DEBUG because it *really* must not ship in RC
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wdeprecated-declarations"
-    threadName = @(dispatch_queue_get_label(dispatch_get_current_queue()));
-#pragma clang diagnostic pop
-#else
-    threadName = [NSString stringWithFormat:@"%p", thread];
-#endif
-  }
-  return threadName;
-}
-
 NSString *RCTFormatLog(
   NSDate *timestamp,
-  NSThread *thread,
   RCTLogLevel level,
   NSString *fileName,
   NSNumber *lineNumber,
@@ -137,9 +120,9 @@ NSString *RCTFormatLog(
   if (level) {
     [log appendFormat:@"[%s]", RCTLogLevels[level - 1]];
   }
-  if (thread) {
-    [log appendFormat:@"[tid:%@]", RCTThreadName(thread)];
-  }
+
+  [log appendFormat:@"[tid:%@]", RCTCurrentThreadName()];
+
   if (fileName) {
     fileName = [fileName lastPathComponent];
     if (lineNumber) {

React/Base/RCTProfile.m

@@ -13,8 +13,8 @@
 
 #import <UIKit/UIKit.h>
 
+#import "RCTAssert.h"
 #import "RCTDefines.h"
-#import "RCTLog.h"
 #import "RCTUtils.h"
 
 #if RCT_DEV
@@ -43,7 +43,7 @@ NSLock *_RCTProfileLock;
 #define RCTProfileAddEvent(type, props...) \
 [RCTProfileInfo[type] addObject:@{ \
   @"pid": @([[NSProcessInfo processInfo] processIdentifier]), \
-  @"tid": RCTThreadName([NSThread currentThread]), \
+  @"tid": RCTCurrentThreadName(), \
   props \
 }];
 

React/Modules/RCTUIManager.m

@@ -390,6 +390,10 @@ static NSDictionary *RCTViewConfigForModule(Class managerClass, NSString *viewNa
 
 - (void)addUIBlock:(RCTViewManagerUIBlock)block
 {
+  RCTAssertThread(_shadowQueue,
+                  @"-[RCTUIManager addUIBlock:] should only be called from the "
+                  "UIManager's _shadowQueue (it may be accessed via `bridge.uiManager.methodQueue`)");
+
   if (!self.isValid) {
     return;
   }