From 99f706e5df45d2390d94de39bf0964e6ab923e91 Mon Sep 17 00:00:00 2001
From: Phillip Pan <phillippan@fb.com>
Date: Fri, 24 Sep 2021 16:57:42 -0700
Subject: [PATCH] introduce RCTComputeScreenScale

Summary:
Changelog: [Internal]

in this diff, we add a function that allows us to retrieve screen scale. enforcing thread safety will be dependent on the consumer to make sure it's used on main thread.

i'd like for this to be a more temporary solution, i think we should have a more scalable screen solution for consumers to handle the gambit of uiscreen use cases.

Reviewed By: sammy-SC

Differential Revision: D31163909

fbshipit-source-id: 78104e9ef982b47c60697461141afb4b06eede72
---
 React/Base/RCTUtils.h |  3 +++
 React/Base/RCTUtils.m | 19 +++++++++++++------
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/React/Base/RCTUtils.h b/React/Base/RCTUtils.h
index 5643035b55e..ecb79159413 100644
--- a/React/Base/RCTUtils.h
+++ b/React/Base/RCTUtils.h
@@ -40,6 +40,9 @@ RCT_EXTERN void RCTExecuteOnMainQueue(dispatch_block_t block);
 // Please do not use this unless you know what you're doing.
 RCT_EXTERN void RCTUnsafeExecuteOnMainQueueSync(dispatch_block_t block);
 
+// Get screen scale, can be only used on main
+RCT_EXTERN void RCTComputeScreenScale(void);
+
 // Get screen metrics in a thread-safe way
 RCT_EXTERN CGFloat RCTScreenScale(void);
 RCT_EXTERN CGFloat RCTFontSizeMultiplier(void);
diff --git a/React/Base/RCTUtils.m b/React/Base/RCTUtils.m
index 6478f8292c2..d33c174e57c 100644
--- a/React/Base/RCTUtils.m
+++ b/React/Base/RCTUtils.m
@@ -296,16 +296,23 @@ static void RCTUnsafeExecuteOnMainQueueOnceSync(dispatch_once_t *onceToken, disp
   }
 }
 
+static dispatch_once_t onceTokenScreenScale;
+static CGFloat screenScale;
+
+void RCTComputeScreenScale()
+{
+  dispatch_once(&onceTokenScreenScale, ^{
+    screenScale = [UIScreen mainScreen].scale;
+  });
+}
+
 CGFloat RCTScreenScale()
 {
-  static dispatch_once_t onceToken;
-  static CGFloat scale;
-
-  RCTUnsafeExecuteOnMainQueueOnceSync(&onceToken, ^{
-    scale = [UIScreen mainScreen].scale;
+  RCTUnsafeExecuteOnMainQueueOnceSync(&onceTokenScreenScale, ^{
+    screenScale = [UIScreen mainScreen].scale;
   });
 
-  return scale;
+  return screenScale;
 }
 
 CGFloat RCTFontSizeMultiplier()