events: add EventEmitterAsyncResource to core

doc/api/events.md

@@ -1166,6 +1166,89 @@ const emitter = new EventEmitter();
 setMaxListeners(5, target, emitter);
 ```
 
+## Class: `events.EventEmitterAsyncResource extends EventEmitter`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+Integrates `EventEmitter` with {AsyncResource} for `EventEmitter`s that
+require manual async tracking. Specifically, all events emitted by instances
+of `events.EventEmitterAsyncResource` will run within its [async context][].
+
+```js
+const { EventEmitterAsyncResource } = require('events');
+const { notStrictEqual, strictEqual } = require('assert');
+const { executionAsyncId } = require('async_hooks');
+
+// Async tracking tooling will identify this as 'Q'.
+const ee1 = new EventEmitterAsyncResource({ name: 'Q' });
+
+// 'foo' listeners will run in the EventEmitters async context.
+ee1.on('foo', () => {
+  strictEqual(executionAsyncId(), ee1.asyncId);
+  strictEqual(triggerAsyncId(), ee1.triggerAsyncId);
+});
+
+const ee2 = new EventEmitter();
+
+// 'foo' listeners on ordinary EventEmitters that do not track async
+// context, however, run in the same async context as the emit().
+ee2.on('foo', () => {
+  notStrictEqual(executionAsyncId(), ee2.asyncId);
+  notStrictEqual(triggerAsyncId(), ee2.triggerAsyncId);
+});
+
+Promise.resolve().then(() => {
+  ee1.emit('foo');
+  ee2.emit('foo');
+});
+```
+
+The `EventEmitterAsyncResource` class has the same methods and takes the
+same options as `EventEmitter` and `AsyncResource` themselves.
+
+### `new events.EventEmitterAsyncResource(options)`
+
+* `options` {Object}
+  * `captureRejections` {boolean} It enables
+    [automatic capturing of promise rejection][capturerejections].
+    **Default:** `false`.
+  * `name` {string} The type of async event. **Default::**
+    [`new.target.name`][].
+  * `triggerAsyncId` {number} The ID of the execution context that created this
+    async event. **Default:** `executionAsyncId()`.
+  * `requireManualDestroy` {boolean} If set to `true`, disables `emitDestroy`
+    when the object is garbage collected. This usually does not need to be set
+    (even if `emitDestroy` is called manually), unless the resource's `asyncId`
+    is retrieved and the sensitive API's `emitDestroy` is called with it.
+    When set to `false`, the `emitDestroy` call on garbage collection
+    will only take place if there is at least one active `destroy` hook.
+    **Default:** `false`.
+
+### `eventemitterasyncresource.asyncId`
+
+* Type: {number} The unique `asyncId` assigned to the resource.
+
+### `eventemitterasyncresource.asyncResource`
+
+* Type: The underlying {AsyncResource}.
+
+The returned `AsyncResource` object has an additional `eventEmitter` property
+that provides a reference to this `EventEmitterAsyncResource`.
+
+### `eventemitterasyncresource.emitDestroy()`
+
+Call all `destroy` hooks. This should only ever be called once. An error will
+be thrown if it is called more than once. This **must** be manually called. If
+the resource is left to be collected by the GC then the `destroy` hooks will
+never be called.
+
+### `eventemitterasyncresource.triggerAsyncId`
+
+* Type: {number} The same `triggerAsyncId` that is passed to the
+  `AsyncResource` constructor.
+
 <a id="event-target-and-event-api"></a>
 
 ## `EventTarget` and `Event` API
@@ -1706,7 +1789,9 @@ to the `EventTarget`.
 [`events.defaultMaxListeners`]: #eventsdefaultmaxlisteners
 [`fs.ReadStream`]: fs.md#class-fsreadstream
 [`net.Server`]: net.md#class-netserver
+[`new.target.name`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new.target
 [`process.on('warning')`]: process.md#event-warning
+[async context]: async_context.md
 [capturerejections]: #capture-rejections-of-promises
 [error]: #error-events
 [rejection]: #emittersymbolfornodejsrejectionerr-eventname-args

lib/events.js

@@ -27,6 +27,7 @@ const {
   ArrayPrototypeShift,
   ArrayPrototypeSlice,
   ArrayPrototypeSplice,
+  ArrayPrototypeUnshift,
   Boolean,
   Error,
   ErrorCaptureStackTrace,
@@ -42,6 +43,7 @@ const {
   Promise,
   PromiseReject,
   PromiseResolve,
+  ReflectApply,
   ReflectOwnKeys,
   String,
   StringPrototypeSplit,
@@ -59,6 +61,7 @@ const {
   kEnhanceStackBeforeInspector,
   codes: {
     ERR_INVALID_ARG_TYPE,
+    ERR_INVALID_THIS,
     ERR_OUT_OF_RANGE,
     ERR_UNHANDLED_ERROR
   },
@@ -68,6 +71,7 @@ const {
   validateAbortSignal,
   validateBoolean,
   validateFunction,
+  validateString,
 } = require('internal/validators');
 
 const kCapture = Symbol('kCapture');
@@ -76,6 +80,125 @@ const kMaxEventTargetListeners = Symbol('events.maxEventTargetListeners');
 const kMaxEventTargetListenersWarned =
   Symbol('events.maxEventTargetListenersWarned');
 
+let EventEmitterAsyncResource;
+// The EventEmitterAsyncResource has to be initialized lazily because event.js
+// is loaded so early in the bootstrap process, before async_hooks is available.
+//
+// This implementation was adapted straight from addaleax's
+// eventemitter-asyncresource MIT-licensed userland module.
+// https://github.com/addaleax/eventemitter-asyncresource
+function lazyEventEmitterAsyncResource() {
+  if (EventEmitterAsyncResource === undefined) {
+    const {
+      AsyncResource
+    } = require('async_hooks');
+
+    const kEventEmitter = Symbol('kEventEmitter');
+    const kAsyncResource = Symbol('kAsyncResource');
+    class EventEmitterReferencingAsyncResource extends AsyncResource {
+      /**
+       * @param {EventEmitter} ee
+       * @param {string} [type]
+       * @param {{
+       *   triggerAsyncId?: number,
+       *   requireManualDestroy?: boolean,
+       * }} [options]
+       */
+      constructor(ee, type, options) {
+        super(type, options);
+        this[kEventEmitter] = ee;
+      }
+
+      /**
+       * @type {EventEmitter}
+       */
+      get eventEmitter() {
+        if (this[kEventEmitter] === undefined)
+          throw new ERR_INVALID_THIS('EventEmitterReferencingAsyncResource');
+        return this[kEventEmitter];
+      }
+    }
+
+    EventEmitterAsyncResource =
+      class EventEmitterAsyncResource extends EventEmitter {
+        /**
+         * @param {{
+         *   name?: string,
+         *   triggerAsyncId?: number,
+         *   requireManualDestroy?: boolean,
+         * }} [options]
+         */
+        constructor(options = undefined) {
+          let name;
+          if (typeof options === 'string') {
+            name = options;
+            options = undefined;
+          } else {
+            if (new.target === EventEmitterAsyncResource) {
+              validateString(options?.name, 'options.name');
+            }
+            name = options?.name || new.target.name;
+          }
+          super(options);
+
+          this[kAsyncResource] =
+            new EventEmitterReferencingAsyncResource(this, name, options);
+        }
+
+        /**
+         * @param {symbol,string} event
+         * @param  {...any} args
+         * @returns {boolean}
+         */
+        emit(event, ...args) {
+          if (this[kAsyncResource] === undefined)
+            throw new ERR_INVALID_THIS('EventEmitterAsyncResource');
+          const { asyncResource } = this;
+          ArrayPrototypeUnshift(args, super.emit, this, event);
+          return ReflectApply(asyncResource.runInAsyncScope, asyncResource,
+                              args);
+        }
+
+        /**
+         * @returns {void}
+         */
+        emitDestroy() {
+          if (this[kAsyncResource] === undefined)
+            throw new ERR_INVALID_THIS('EventEmitterAsyncResource');
+          this.asyncResource.emitDestroy();
+        }
+
+        /**
+         * @type {number}
+         */
+        get asyncId() {
+          if (this[kAsyncResource] === undefined)
+            throw new ERR_INVALID_THIS('EventEmitterAsyncResource');
+          return this.asyncResource.asyncId();
+        }
+
+        /**
+         * @type {number}
+         */
+        get triggerAsyncId() {
+          if (this[kAsyncResource] === undefined)
+            throw new ERR_INVALID_THIS('EventEmitterAsyncResource');
+          return this.asyncResource.triggerAsyncId();
+        }
+
+        /**
+         * @type {EventEmitterReferencingAsyncResource}
+         */
+        get asyncResource() {
+          if (this[kAsyncResource] === undefined)
+            throw new ERR_INVALID_THIS('EventEmitterAsyncResource');
+          return this[kAsyncResource];
+        }
+      };
+  }
+  return EventEmitterAsyncResource;
+}
+
 /**
  * Creates a new `EventEmitter` instance.
  * @param {{ captureRejections?: boolean; }} [opts]
@@ -106,6 +229,13 @@ ObjectDefineProperty(EventEmitter, 'captureRejections', {
   enumerable: true
 });
 
+ObjectDefineProperty(EventEmitter, 'EventEmitterAsyncResource', {
+  enumerable: true,
+  get: lazyEventEmitterAsyncResource,
+  set: undefined,
+  configurable: true,
+});
+
 EventEmitter.errorMonitor = kErrorMonitor;
 
 // The default for captureRejections is false