JS side implementation of PerformanceObserver API

Summary:
[Changelog][Internal]

This adds module specs for the native part of PerformanceObserver, as well as the interaction logic vs the NativePerformanceObserver API.

See https://fb.quip.com/MdqgAk1Eb2dV for more detail.

Reviewed By: rubennorte

Differential Revision: D40897006

fbshipit-source-id: 77475f21dad9ee9dbe15df5a989eb08d314e6db2

Author: rshest

Libraries/NativeModules/specs/NativePerformanceObserverCxx.js

@@ -0,0 +1,44 @@
+/**
+ * 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.
+ *
+ * @flow strict
+ * @format
+ */
+
+import type {TurboModule} from '../../TurboModule/RCTExport';
+
+import * as TurboModuleRegistry from '../../TurboModule/TurboModuleRegistry';
+
+export type RawTimeStamp = number;
+
+export const RawPerformanceEntryTypeValues = {
+  UNDEFINED: 0,
+};
+
+export type RawPerformanceEntryType = number;
+
+export type RawPerformanceEntry = $ReadOnly<{
+  name: string,
+  entryType: RawPerformanceEntryType,
+  startTime: RawTimeStamp,
+  duration: number,
+
+  // For "event" entries only:
+  processingStart?: RawTimeStamp,
+  processingEnd?: RawTimeStamp,
+  interactionId?: RawTimeStamp,
+}>;
+
+export type RawPerformanceEntryList = $ReadOnlyArray<RawPerformanceEntry>;
+
+export interface Spec extends TurboModule {
+  +startReporting: (entryType: string) => void;
+  +stopReporting: (entryType: string) => void;
+  +getPendingEntries: () => RawPerformanceEntryList;
+  +setOnPerformanceEntryCallback: (callback?: () => void) => void;
+}
+
+export default (TurboModuleRegistry.get<Spec>('PerformanceObserver'): ?Spec);

Libraries/WebPerformance/PerformanceObserver.js

@@ -8,16 +8,38 @@
  * @flow strict
  */
 
+import type {
+  RawPerformanceEntry,
+  RawPerformanceEntryList,
+  RawPerformanceEntryType,
+} from '../NativeModules/specs/NativePerformanceObserverCxx';
+
+import NativePerformanceObserver from '../NativeModules/specs/NativePerformanceObserverCxx';
+import warnOnce from '../Utilities/warnOnce';
+
 export type HighResTimeStamp = number;
-// TODO: Extend once new types (such as event) are supported
-export type PerformanceEntryType = empty;
+// TODO: Extend once new types (such as event) are supported.
+// TODO: Get rid of the "undefined" once there is at least one type supported.
+export type PerformanceEntryType = 'undefined';
 
 export class PerformanceEntry {
   name: string;
   entryType: PerformanceEntryType;
   startTime: HighResTimeStamp;
   duration: number;
 
+  constructor(init: {
+    name: string,
+    entryType: PerformanceEntryType,
+    startTime: HighResTimeStamp,
+    duration: number,
+  }) {
+    this.name = init.name;
+    this.entryType = init.entryType;
+    this.startTime = init.startTime;
+    this.duration = init.duration;
+  }
+
   // $FlowIgnore: Flow(unclear-type)
   toJSON(): Object {
     return {
@@ -29,6 +51,21 @@ export class PerformanceEntry {
   }
 }
 
+function rawToPerformanceEntryType(
+  type: RawPerformanceEntryType,
+): PerformanceEntryType {
+  return 'undefined';
+}
+
+function rawToPerformanceEntry(entry: RawPerformanceEntry): PerformanceEntry {
+  return new PerformanceEntry({
+    name: entry.name,
+    entryType: rawToPerformanceEntryType(entry.entryType),
+    startTime: entry.startTime,
+    duration: entry.duration,
+  });
+}
+
 export type PerformanceEntryList = $ReadOnlyArray<PerformanceEntry>;
 
 export class PerformanceObserverEntryList {
@@ -73,6 +110,19 @@ export type PerformanceObserverInit =
       type: PerformanceEntryType,
     };
 
+let _observedEntryTypeRefCount: Map<PerformanceEntryType, number> = new Map();
+
+let _observers: Set<PerformanceObserver> = new Set();
+
+let _onPerformanceEntryCallbackIsSet: boolean = false;
+
+function warnNoNativePerformanceObserver() {
+  warnOnce(
+    'missing-native-performance-observer',
+    'Missing native implementation of PerformanceObserver',
+  );
+}
+
 /**
  * Implementation of the PerformanceObserver interface for RN,
  * corresponding to the standard in https://www.w3.org/TR/performance-timeline/
@@ -95,24 +145,81 @@ export type PerformanceObserverInit =
  */
 export default class PerformanceObserver {
   _callback: PerformanceObserverCallback;
+  _entryTypes: $ReadOnlySet<PerformanceEntryType>;
 
   constructor(callback: PerformanceObserverCallback) {
     this._callback = callback;
   }
 
   observe(options: PerformanceObserverInit) {
-    console.log('PerformanceObserver: started observing');
+    if (!NativePerformanceObserver) {
+      warnNoNativePerformanceObserver();
+      return;
+    }
+    if (!_onPerformanceEntryCallbackIsSet) {
+      NativePerformanceObserver.setOnPerformanceEntryCallback(
+        onPerformanceEntry,
+      );
+      _onPerformanceEntryCallbackIsSet = true;
+    }
+    if (options.entryTypes) {
+      this._entryTypes = new Set(options.entryTypes);
+    } else {
+      this._entryTypes = new Set([options.type]);
+    }
+    this._entryTypes.forEach(type => {
+      if (!_observedEntryTypeRefCount.has(type)) {
+        NativePerformanceObserver.startReporting(type);
+      }
+      _observedEntryTypeRefCount.set(
+        type,
+        (_observedEntryTypeRefCount.get(type) ?? 0) + 1,
+      );
+    });
+    _observers.add(this);
   }
 
   disconnect(): void {
-    console.log('PerformanceObserver: stopped observing');
-  }
-
-  takeRecords(): PerformanceEntryList {
-    return [];
+    if (!NativePerformanceObserver) {
+      warnNoNativePerformanceObserver();
+      return;
+    }
+    this._entryTypes.forEach(type => {
+      const entryTypeRefCount = _observedEntryTypeRefCount.get(type) ?? 0;
+      if (entryTypeRefCount === 1) {
+        _observedEntryTypeRefCount.delete(type);
+        NativePerformanceObserver.stopReporting(type);
+      } else if (entryTypeRefCount !== 0) {
+        _observedEntryTypeRefCount.set(type, entryTypeRefCount - 1);
+      }
+    });
+    _observers.delete(this);
+    if (_observers.size === 0) {
+      NativePerformanceObserver.setOnPerformanceEntryCallback();
+      _onPerformanceEntryCallbackIsSet = false;
+    }
   }
 
   static supportedEntryTypes: $ReadOnlyArray<PerformanceEntryType> =
     // TODO: add types once they are fully supported
     Object.freeze([]);
 }
+
+// This is a callback that gets scheduled and periodically called from the native side
+function onPerformanceEntry() {
+  if (!NativePerformanceObserver) {
+    return;
+  }
+  const rawEntries: RawPerformanceEntryList =
+    NativePerformanceObserver.getPendingEntries();
+  const entries = rawEntries.map(rawToPerformanceEntry);
+  _observers.forEach(observer => {
+    const entriesForObserver: PerformanceEntryList = entries.filter(entry =>
+      observer._entryTypes.has(entry.entryType),
+    );
+    observer._callback(
+      new PerformanceObserverEntryList(entriesForObserver),
+      observer,
+    );
+  });
+}