From 1452954c4c5d15b04bc80fad359b2cf4f44addb3 Mon Sep 17 00:00:00 2001
From: Kevin Gozali <fkg@fb.com>
Date: Fri, 27 Sep 2019 13:42:45 -0700
Subject: [PATCH] TM: Add mutex to access LongLivedObjectCollection - making it
 thread safe

Summary:
There are cases where the CallbackWrapper instances were added from different thread, potentially crashing the inner std::unordered_set<> we're using to keep the wrappers alive for extended time.

To avoid it, let's just use std::mutex.

Reviewed By: shergin

Differential Revision: D17631233

fbshipit-source-id: e8f98004e45a68be31f8f0cda118fb67dcb06d45
---
 ReactCommon/turbomodule/core/LongLivedObject.cpp |  9 ++++++---
 ReactCommon/turbomodule/core/LongLivedObject.h   | 12 +++++++-----
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/ReactCommon/turbomodule/core/LongLivedObject.cpp b/ReactCommon/turbomodule/core/LongLivedObject.cpp
index a56ddd11125..6598bb2d19c 100644
--- a/ReactCommon/turbomodule/core/LongLivedObject.cpp
+++ b/ReactCommon/turbomodule/core/LongLivedObject.cpp
@@ -18,11 +18,13 @@ LongLivedObjectCollection &LongLivedObjectCollection::get() {
 
 LongLivedObjectCollection::LongLivedObjectCollection() {}
 
-void LongLivedObjectCollection::add(std::shared_ptr<LongLivedObject> so) {
+void LongLivedObjectCollection::add(std::shared_ptr<LongLivedObject> so) const {
+  std::lock_guard<std::mutex> lock(collectionMutex_);
   collection_.insert(so);
 }
 
-void LongLivedObjectCollection::remove(const LongLivedObject *o) {
+void LongLivedObjectCollection::remove(const LongLivedObject *o) const {
+  std::lock_guard<std::mutex> lock(collectionMutex_);
   auto p = collection_.begin();
   for (; p != collection_.end(); p++) {
     if (p->get() == o) {
@@ -34,7 +36,8 @@ void LongLivedObjectCollection::remove(const LongLivedObject *o) {
   }
 }
 
-void LongLivedObjectCollection::clear() {
+void LongLivedObjectCollection::clear() const {
+  std::lock_guard<std::mutex> lock(collectionMutex_);
   collection_.clear();
 }
 
diff --git a/ReactCommon/turbomodule/core/LongLivedObject.h b/ReactCommon/turbomodule/core/LongLivedObject.h
index f390029a568..ee5039b52da 100644
--- a/ReactCommon/turbomodule/core/LongLivedObject.h
+++ b/ReactCommon/turbomodule/core/LongLivedObject.h
@@ -8,6 +8,7 @@
 #pragma once
 
 #include <memory>
+#include <mutex>
 #include <unordered_set>
 
 namespace facebook {
@@ -32,7 +33,7 @@ class LongLivedObject {
 };
 
 /**
- * A singleton collection for the `LongLivedObject`s.
+ * A singleton, thread-safe, write-only collection for the `LongLivedObject`s.
  */
 class LongLivedObjectCollection {
  public:
@@ -41,13 +42,14 @@ class LongLivedObjectCollection {
   LongLivedObjectCollection(LongLivedObjectCollection const &) = delete;
   void operator=(LongLivedObjectCollection const &) = delete;
 
-  void add(std::shared_ptr<LongLivedObject> o);
-  void remove(const LongLivedObject *o);
-  void clear();
+  void add(std::shared_ptr<LongLivedObject> o) const;
+  void remove(const LongLivedObject *o) const;
+  void clear() const;
 
  private:
   LongLivedObjectCollection();
-  std::unordered_set<std::shared_ptr<LongLivedObject>> collection_;
+  mutable std::unordered_set<std::shared_ptr<LongLivedObject>> collection_;
+  mutable std::mutex collectionMutex_;
 };
 
 } // namespace react