move rncxx utils (#50668)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/50668

Changelog: [Internal]

Reviewed By: zeyap

Differential Revision: D72800712

fbshipit-source-id: f966906d10df1fac818fc9998dbe5e0b8d67be3f

packages/react-native/ReactCxxPlatform/react/utils/EnumHelper.h

@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and 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 <type_traits>
+
+namespace std {
+
+// mimics the c++23 std::to_underlying
+template <class Enum>
+constexpr auto to_underlying(Enum e) noexcept {
+  return static_cast<std::underlying_type_t<Enum>>(e);
+}
+
+} // namespace std

packages/react-native/ReactCxxPlatform/react/utils/PlatformRunLoopObserver.h

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and 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 <react/utils/RunLoopObserver.h>
+#include <functional>
+#include <utility>
+
+namespace facebook::react {
+
+class PlatformRunLoopObserver;
+
+class PlatformRunLoopObserver : public RunLoopObserver {
+ public:
+  PlatformRunLoopObserver(
+      RunLoopObserver::Activity activities,
+      const RunLoopObserver::WeakOwner& owner)
+      : RunLoopObserver(activities, owner) {}
+  ~PlatformRunLoopObserver() override = default;
+
+  PlatformRunLoopObserver(PlatformRunLoopObserver& other) = delete;
+  PlatformRunLoopObserver& operator=(PlatformRunLoopObserver& other) = delete;
+  PlatformRunLoopObserver(PlatformRunLoopObserver&& other) = delete;
+  PlatformRunLoopObserver& operator=(PlatformRunLoopObserver&& other) = delete;
+
+  bool isOnRunLoopThread() const noexcept override {
+    return false;
+  }
+
+  void onRender() const noexcept {
+    if (auto owner = owner_.lock()) {
+      activityDidChange(activities_);
+    }
+  }
+
+ private:
+  void startObserving() const noexcept override {}
+  void stopObserving() const noexcept override {}
+};
+
+} // namespace facebook::react

packages/react-native/ReactCxxPlatform/react/utils/RunLoopObserverManager.cpp

@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include "RunLoopObserverManager.h"
+
+#include <react/debug/react_native_assert.h>
+
+namespace facebook::react {
+
+/*
+ * Event beat associated with JavaScript runtime. The beat is called on
+ * RuntimeScheduler's thread induced by the UI thread event loop.
+ */
+class EventBeatImpl : public EventBeat, public RunLoopObserver::Delegate {
+ public:
+  EventBeatImpl(
+      std::shared_ptr<OwnerBox> ownerBox,
+      std::shared_ptr<const RunLoopObserver> uiRunLoopObserver,
+      RuntimeScheduler& runtimeScheduler)
+      : EventBeat(std::move(ownerBox), runtimeScheduler),
+        uiRunLoopObserver_(std::move(uiRunLoopObserver)) {
+    uiRunLoopObserver_->setDelegate(this);
+    uiRunLoopObserver_->enable();
+  }
+
+#pragma mark - RunLoopObserver::Delegate
+
+  void activityDidChange(
+      const RunLoopObserver::Delegate* delegate,
+      RunLoopObserver::Activity /*activity*/) const noexcept override {
+    react_native_assert(delegate == this);
+    induce();
+  }
+
+ private:
+  std::shared_ptr<const RunLoopObserver> uiRunLoopObserver_;
+};
+
+std::unique_ptr<EventBeat> RunLoopObserverManager::createEventBeat(
+    std::shared_ptr<EventBeat::OwnerBox> ownerBox,
+    RuntimeScheduler& runtimeScheduler) {
+  auto observer = std::make_shared<const PlatformRunLoopObserver>(
+      RunLoopObserver::Activity::BeforeWaiting, ownerBox->owner);
+  observer_ = observer;
+  return std::make_unique<EventBeatImpl>(
+      std::move(ownerBox), std::move(observer), runtimeScheduler);
+}
+
+void RunLoopObserverManager::onRender() const noexcept {
+  if (auto observer = observer_.lock()) {
+    observer->onRender();
+  }
+}
+
+} // namespace facebook::react

packages/react-native/ReactCxxPlatform/react/utils/RunLoopObserverManager.h

@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and 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 "PlatformRunLoopObserver.h"
+
+#include <react/renderer/core/EventBeat.h>
+#include <react/renderer/runtimescheduler/RuntimeScheduler.h>
+#include <memory>
+
+namespace facebook::react {
+
+class RunLoopObserverManager
+    : std::enable_shared_from_this<RunLoopObserverManager> {
+ public:
+  std::unique_ptr<EventBeat> createEventBeat(
+      std::shared_ptr<EventBeat::OwnerBox> ownerBox,
+      RuntimeScheduler& runtimeScheduler);
+
+  void onRender() const noexcept;
+
+  void induce() const noexcept;
+
+ private:
+  std::weak_ptr<const PlatformRunLoopObserver> observer_;
+};
+
+} // namespace facebook::react