From 366fa2f1ef442bf30da17ec82131a59bb1b7906b Mon Sep 17 00:00:00 2001
From: Spencer Ahrens <sahrens@fb.com>
Date: Fri, 29 Mar 2019 10:27:20 -0700
Subject: [PATCH] use shared mutex in RCTSurfacePresenter

Summary:
Otherwise reloading from metro deadlocks like this:
`[RCTSurfaceRegistry _stopAllSurfaces]` is calling `[RCTSurfaceRegistry enumerateWithBlock]` which locks `_mutex` and then we call `surfaceForRootTag` which then deadlocks on the same mutex:
https://pxl.cl/tmm1

Reviewed By: shergin

Differential Revision: D14679843

fbshipit-source-id: 9f4ecdfa7a79fcf7f3fc2ce437d4399b00910f26
---
 React/Fabric/RCTSurfaceRegistry.mm | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/React/Fabric/RCTSurfaceRegistry.mm b/React/Fabric/RCTSurfaceRegistry.mm
index 76bbf8f86..0eae535f4 100644
--- a/React/Fabric/RCTSurfaceRegistry.mm
+++ b/React/Fabric/RCTSurfaceRegistry.mm
@@ -8,11 +8,15 @@
 #import "RCTSurfaceRegistry.h"
 
 #import <mutex>
+#import <shared_mutex>
+#import <better/mutex.h>
 
 #import <React/RCTFabricSurface.h>
 
+using namespace facebook;
+
 @implementation RCTSurfaceRegistry {
-  std::mutex _mutex;
+  better::shared_mutex _mutex;
   NSMapTable<id, RCTFabricSurface *> *_registry;
 }
 
@@ -28,13 +32,13 @@
 
 - (void)enumerateWithBlock:(RCTSurfaceEnumeratorBlock)block
 {
-  std::lock_guard<std::mutex> lock(_mutex);
+  std::shared_lock<better::shared_mutex> lock(_mutex);
   block([_registry objectEnumerator]);
 }
 
 - (void)registerSurface:(RCTFabricSurface *)surface
 {
-  std::lock_guard<std::mutex> lock(_mutex);
+  std::unique_lock<better::shared_mutex> lock(_mutex);
 
   ReactTag rootTag = surface.rootViewTag.integerValue;
   [_registry setObject:surface forKey:(__bridge id)(void *)rootTag];
@@ -42,7 +46,7 @@
 
 - (void)unregisterSurface:(RCTFabricSurface *)surface
 {
-  std::lock_guard<std::mutex> lock(_mutex);
+  std::unique_lock<better::shared_mutex> lock(_mutex);
 
   ReactTag rootTag = surface.rootViewTag.integerValue;
   [_registry removeObjectForKey:(__bridge id)(void *)rootTag];
@@ -50,7 +54,7 @@
 
 - (RCTFabricSurface *)surfaceForRootTag:(ReactTag)rootTag
 {
-  std::lock_guard<std::mutex> lock(_mutex);
+  std::shared_lock<better::shared_mutex> lock(_mutex);
 
   return [_registry objectForKey:(__bridge id)(void *)rootTag];
 }