Fabric: Introducing `TelemetryController` as part of `MountingManager`

Summary:
This diff implements TelemetryController, a small tool that can be used to instrument mounting transactions. It abstracts the logic of merging telemetry data of multiple transactions in a thread-safe manner.

Changelog: [Internal] Fabric-specific internal change.

Reviewed By: sammy-SC

Differential Revision: D22490580

fbshipit-source-id: 3f3425b88d38fddb555c1390fd8f1ff3ef1c475a

ReactCommon/fabric/mounting/MountingCoordinator.cpp

@@ -24,7 +24,8 @@ MountingCoordinator::MountingCoordinator(
     std::weak_ptr<MountingOverrideDelegate const> delegate)
     : surfaceId_(baseRevision.getRootShadowNode().getSurfaceId()),
       baseRevision_(baseRevision),
-      mountingOverrideDelegate_(delegate) {
+      mountingOverrideDelegate_(delegate),
+      telemetryController_(*this) {
 #ifdef RN_SHADOW_TREE_INTROSPECTION
   stubViewTree_ = stubViewTreeFromShadowNode(baseRevision_.getRootShadowNode());
 #endif
@@ -172,5 +173,9 @@ better::optional<MountingTransaction> MountingCoordinator::pullTransaction()
   return transaction;
 }
 
+TelemetryController const &MountingCoordinator::getTelemetryController() const {
+  return telemetryController_;
+}
+
 } // namespace react
 } // namespace facebook

ReactCommon/fabric/mounting/MountingCoordinator.h

@@ -14,6 +14,7 @@
 #include <react/mounting/MountingOverrideDelegate.h>
 #include <react/mounting/MountingTransaction.h>
 #include <react/mounting/ShadowTreeRevision.h>
+#include <react/mounting/TelemetryController.h>
 #include "ShadowTreeRevision.h"
 
 #ifdef RN_SHADOW_TREE_INTROSPECTION
@@ -69,6 +70,8 @@ class MountingCoordinator final {
    */
   bool waitForTransaction(std::chrono::duration<double> timeout) const;
 
+  TelemetryController const &getTelemetryController() const;
+
   /*
    * Methods from this section are meant to be used by
    * `MountingOverrideDelegate` only.
@@ -104,6 +107,8 @@ class MountingCoordinator final {
   mutable std::condition_variable signal_;
   std::weak_ptr<MountingOverrideDelegate const> mountingOverrideDelegate_;
 
+  TelemetryController telemetryController_;
+
 #ifdef RN_SHADOW_TREE_INTROSPECTION
   void validateTransactionAgainstStubViewTree(
       ShadowViewMutationList const &mutations,

ReactCommon/fabric/mounting/TelemetryController.cpp

@@ -0,0 +1,58 @@
+/*
+ * 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.
+ */
+
+#include "TelemetryController.h"
+
+#include <react/mounting/MountingCoordinator.h>
+
+namespace facebook {
+namespace react {
+
+TelemetryController::TelemetryController(
+    MountingCoordinator const &mountingCoordinator) noexcept
+    : mountingCoordinator_(mountingCoordinator) {}
+
+bool TelemetryController::pullTransaction(
+    std::function<void(MountingTransactionMetadata metadata)> willMount,
+    std::function<void(ShadowViewMutationList const &mutations)> doMount,
+    std::function<void(MountingTransactionMetadata metadata)> didMount) const
+    noexcept {
+  auto optional = mountingCoordinator_.pullTransaction();
+  if (!optional.has_value()) {
+    return false;
+  }
+
+  auto transaction = std::move(*optional);
+
+  auto surfaceId = transaction.getSurfaceId();
+  auto number = transaction.getNumber();
+  auto telemetry = transaction.getTelemetry();
+  auto numberOfMutations = transaction.getMutations().size();
+
+  mutex_.lock();
+  auto compoundTelemetry = compoundTelemetry_;
+  mutex_.unlock();
+
+  willMount({surfaceId, number, telemetry, compoundTelemetry});
+
+  telemetry.willMount();
+  doMount(std::move(transaction.getMutations()));
+  telemetry.didMount();
+
+  compoundTelemetry.incorporate(telemetry, numberOfMutations);
+
+  didMount({surfaceId, number, telemetry, compoundTelemetry});
+
+  mutex_.lock();
+  compoundTelemetry_ = compoundTelemetry;
+  mutex_.unlock();
+
+  return true;
+}
+
+} // namespace react
+} // namespace facebook

ReactCommon/fabric/mounting/TelemetryController.h

@@ -0,0 +1,58 @@
+/*
+ * 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 <functional>
+#include <mutex>
+
+#include <react/mounting/MountingTelemetry.h>
+#include <react/mounting/MountingTransaction.h>
+#include <react/mounting/MountingTransactionMetadata.h>
+
+namespace facebook {
+namespace react {
+
+class MountingCoordinator;
+
+/*
+ * Provides convenient tools for aggregating and accessing telemetry data
+ * associated with running Surface.
+ */
+class TelemetryController final {
+  friend class MountingCoordinator;
+
+  /*
+   * To be used by `MountingCoordinator`.
+   */
+  TelemetryController(MountingCoordinator const &mountingCoordinator) noexcept;
+
+  /*
+   * Not copyable.
+   */
+  TelemetryController(TelemetryController const &other) noexcept = delete;
+  TelemetryController &operator=(TelemetryController const &other) noexcept =
+      delete;
+
+ public:
+  /*
+   * Calls `MountingCoordinator::pullTransaction()` and aggregates telemetry.
+   */
+  bool pullTransaction(
+      std::function<void(MountingTransactionMetadata metadata)> willMount,
+      std::function<void(ShadowViewMutationList const &mutations)> doMount,
+      std::function<void(MountingTransactionMetadata metadata)> didMount) const
+      noexcept;
+
+ private:
+  MountingCoordinator const &mountingCoordinator_;
+  mutable SurfaceTelemetry compoundTelemetry_{};
+  mutable std::mutex mutex_;
+};
+
+} // namespace react
+} // namespace facebook