From 193a2bd4cdffbbc79b69c067b31420663dc9b03a Mon Sep 17 00:00:00 2001
From: Valentin Shergin <shergin@fb.com>
Date: Tue, 16 Jan 2018 12:11:23 -0800
Subject: [PATCH] Tweaking -[RCTSurface synchronouslyWaitForStage:]

Summary: Waiting for layout is now available on main thread.

Reviewed By: mmmulani

Differential Revision: D6719836

fbshipit-source-id: ef655095e999df5f77e69c5931459cce1aaeb1f0
---
 React/Base/Surface/RCTSurface.h  |  9 ++++++---
 React/Base/Surface/RCTSurface.mm | 20 ++++++++++----------
 2 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/React/Base/Surface/RCTSurface.h b/React/Base/Surface/RCTSurface.h
index 603f0e851acf1b..44a53f6569cba5 100644
--- a/React/Base/Surface/RCTSurface.h
+++ b/React/Base/Surface/RCTSurface.h
@@ -84,7 +84,6 @@ NS_ASSUME_NONNULL_BEGIN
  */
 @property (atomic, assign, readonly) CGSize maximumSize;
 
-
 /**
  * Simple shortcut to `-[RCTSurface setMinimumSize:size maximumSize:size]`.
  */
@@ -109,8 +108,12 @@ NS_ASSUME_NONNULL_BEGIN
 
 /**
  * Synchronously blocks the current thread up to given `timeout` until
- * the Surface will not have given `stage`.
- * Do nothing, if called from the main or `UIManager` queue.
+ * the Surface reaches `stage`.
+ * Limitations:
+ *  - Do nothing, if called on `UIManager` queue.
+ *  - Calling on the main queue with `RCTSurfaceStageSurfaceDidInitialMounting`
+ *    stage temporary is not supported; in this case the stage will be
+ *    downgraded to `RCTSurfaceStageSurfaceDidInitialLayout`.
  */
 - (BOOL)synchronouslyWaitForStage:(RCTSurfaceStage)stage timeout:(NSTimeInterval)timeout;
 
diff --git a/React/Base/Surface/RCTSurface.mm b/React/Base/Surface/RCTSurface.mm
index 736400953d535b..5002c9f6dd3b62 100644
--- a/React/Base/Surface/RCTSurface.mm
+++ b/React/Base/Surface/RCTSurface.mm
@@ -435,6 +435,16 @@ - (CGSize)intrinsicSize
 
 - (BOOL)synchronouslyWaitForStage:(RCTSurfaceStage)stage timeout:(NSTimeInterval)timeout
 {
+  if (RCTIsMainQueue() && (stage == RCTSurfaceStageSurfaceDidInitialRendering)) {
+    // This case *temporary* does not supported.
+    stage = RCTSurfaceStageSurfaceDidInitialLayout;
+  }
+
+  if (RCTIsUIManagerQueue()) {
+    RCTLogInfo(@"Synchronous waiting is not supported on UIManager queue.");
+    return NO;
+  }
+
   dispatch_semaphore_t semaphore;
   switch (stage) {
     case RCTSurfaceStageSurfaceDidInitialLayout:
@@ -447,16 +457,6 @@ - (BOOL)synchronouslyWaitForStage:(RCTSurfaceStage)stage timeout:(NSTimeInterval
       RCTAssert(NO, @"Only waiting for `RCTSurfaceStageSurfaceDidInitialRendering` and `RCTSurfaceStageSurfaceDidInitialLayout` stages is supported.");
   }
 
-  if (RCTIsMainQueue()) {
-    RCTLogInfo(@"Synchronous waiting is not supported on the main queue.");
-    return NO;
-  }
-
-  if (RCTIsUIManagerQueue()) {
-    RCTLogInfo(@"Synchronous waiting is not supported on UIManager queue.");
-    return NO;
-  }
-
   BOOL timeoutOccured = dispatch_semaphore_wait(semaphore, dispatch_time(DISPATCH_TIME_NOW, timeout * NSEC_PER_SEC));
   if (!timeoutOccured) {
     // Balancing the semaphore.