Remove ThreadStorage class in favour of thread_local

Summary:
#changelog: [internal]

When I built ThreadStorage I didn't know about existence of `thread_local` keyword. Because it achieves the same goal, using built in c++ features is preferred over building our own.

Reviewed By: JoshuaGross, shergin

Differential Revision: D24380680

fbshipit-source-id: e961fc34c6d3f085fc9b918b20bb4827de0d5624

ReactCommon/react/renderer/components/view/YogaLayoutableShadowNode.cpp

@@ -12,7 +12,6 @@
 #include <react/renderer/core/LayoutContext.h>
 #include <react/renderer/debug/DebugStringConvertibleItem.h>
 #include <react/renderer/debug/SystraceSection.h>
-#include <react/utils/ThreadStorage.h>
 #include <yoga/Yoga.h>
 #include <algorithm>
 #include <limits>
@@ -21,6 +20,8 @@
 namespace facebook {
 namespace react {
 
+thread_local LayoutContext threadLocalLayoutContext;
+
 static void applyLayoutConstraints(
     YGStyle &yogaStyle,
     LayoutConstraints const &layoutConstraints) {
@@ -332,7 +333,7 @@ void YogaLayoutableShadowNode::layoutTree(
 
   applyLayoutConstraints(yogaNode_.getStyle(), layoutConstraints);
 
-  ThreadStorage<LayoutContext>::getInstance().set(layoutContext);
+  threadLocalLayoutContext = layoutContext;
 
   if (layoutContext.swapLeftAndRightInRTL) {
     swapLeftAndRightInTree(*this);
@@ -492,10 +493,8 @@ YGSize YogaLayoutableShadowNode::yogaNodeMeasureCallbackConnector(
       break;
   }
 
-  auto layoutContext = ThreadStorage<LayoutContext>::getInstance().get();
-
   auto size = shadowNodeRawPtr->measureContent(
-      layoutContext.value_or(LayoutContext{}), {minimumSize, maximumSize});
+      threadLocalLayoutContext, {minimumSize, maximumSize});
 
   return YGSize{yogaFloatFromFloat(size.width),
                 yogaFloatFromFloat(size.height)};

ReactCommon/react/utils/ThreadStorage.h

@@ -1,57 +0,0 @@
-/*
- * Copyright (c) Facebook, Inc. and its affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- */
-
-#pragma once
-
-#include <better/map.h>
-#include <better/optional.h>
-#include <mutex>
-#include <thread>
-
-namespace facebook {
-namespace react {
-
-/*
- * ThreadStorage is a class designed to store data for specific thread.
- * When data is inserted from thread 1, it can only be retrieved from thread 1.
- */
-template <typename DataT>
-class ThreadStorage {
-  /*
-   * Private default constructor. This class has to be used as a singleton.
-   */
-  ThreadStorage() = default;
-
- public:
-  static ThreadStorage<DataT> &getInstance() {
-    static ThreadStorage<DataT> threadStorage;
-    return threadStorage;
-  }
-
-  better::optional<DataT> get() const {
-    std::lock_guard<std::mutex> lock(mutex_);
-    auto iterator = storage_.find(std::this_thread::get_id());
-
-    if (iterator != storage_.end()) {
-      return iterator->second;
-    } else {
-      return {};
-    }
-  }
-
-  void set(DataT data) {
-    std::lock_guard<std::mutex> lock(mutex_);
-    storage_[std::this_thread::get_id()] = data;
-  }
-
- private:
-  mutable std::mutex mutex_;
-  better::map<std::thread::id, DataT> storage_;
-};
-
-} // namespace react
-} // namespace facebook