From 70f683b9e1ffc1c3661e68dea6a393af0b0edb0a Mon Sep 17 00:00:00 2001
From: Sidharth Guglani <sidharthguglani@fb.com>
Date: Sun, 19 May 2019 23:29:28 -0700
Subject: [PATCH] mutex lock while accessing event subscribers vector for
 thread safety

Summary: Using Mutex lock_guard mechanism when writing to subscribers and when accessing them in publish to make a copy

Reviewed By: davidaurelio

Differential Revision: D15391679

fbshipit-source-id: 16713ff28ce1762a5ca4c48c152897a92417e80b
---
 ReactCommon/yoga/yoga/event/event.cpp | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/ReactCommon/yoga/yoga/event/event.cpp b/ReactCommon/yoga/yoga/event/event.cpp
index 167912a9f6e1f5..e2fe3588f1f96d 100644
--- a/ReactCommon/yoga/yoga/event/event.cpp
+++ b/ReactCommon/yoga/yoga/event/event.cpp
@@ -34,11 +34,19 @@ void Event::reset() {
 
 void Event::subscribe(std::function<Subscriber>&& subscriber) {
   std::lock_guard<std::mutex> guard(eventSubscribersMutex());
+  eventSubscribers() =
+      std::make_shared<Event::Subscribers>(*eventSubscribers());
   eventSubscribers()->push_back(subscriber);
 }
 
 void Event::publish(const YGNode& node, Type eventType, const Data& eventData) {
-  for (auto& subscriber : *eventSubscribers()) {
+  std::shared_ptr<Event::Subscribers> subscribers;
+  {
+    std::lock_guard<std::mutex> guard(eventSubscribersMutex());
+    subscribers = eventSubscribers();
+  }
+
+  for (auto& subscriber : *subscribers) {
     if (subscriber) {
       subscriber(node, eventType, eventData);
     }