worker: add experimental BroadcastChannel

Signed-off-by: James M Snell <jasnell@gmail.com>

PR-URL: #36271
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

doc/api/worker_threads.md

@@ -274,6 +274,98 @@ if (isMainThread) {
 }
 ```
 
+## Class: `BroadcastChannel extends EventTarget`
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+Instances of `BroadcastChannel` allow asynchronous one-to-many communication
+with all other `BroadcastChannel` instances bound to the same channel name.
+
+```js
+'use strict';
+
+const {
+  isMainThread,
+  BroadcastChannel,
+  Worker
+} = require('worker_threads');
+
+const bc = new BroadcastChannel('hello');
+
+if (isMainThread) {
+  let c = 0;
+  bc.onmessage = (event) => {
+    console.log(event.data);
+    if (++c === 10) bc.close();
+  };
+  for (let n = 0; n < 10; n++)
+    new Worker(__filename);
+} else {
+  bc.postMessage('hello from every worker');
+  bc.close();
+}
+```
+
+### `new BroadcastChannel(name)`
+<!-- YAML
+added: REPLACEME
+-->
+
+* `name` {any} The name of the channel to connect to. Any JavaScript value
+  that can be converted to a string using ``${name}`` is permitted.
+
+### `broadcastChannel.close()`
+<!-- YAML
+added: REPLACEME
+-->
+
+Closes the `BroadcastChannel` connection.
+
+### `broadcastChannel.onmessage`
+<!-- YAML
+added: REPLACEME
+-->
+
+* Type: {Function} Invoked with a single `MessageEvent` argument
+  when a message is received.
+
+### `broadcastChannel.onmessageerror`
+<!-- YAML
+added: REPLACEME
+-->
+
+* Type: {Function} Invoked with a received message cannot be
+  deserialized.
+
+### `broadcastChannel.postMessage(message)`
+<!-- YAML
+added: REPLACEME
+-->
+
+* `message` {any} Any cloneable JavaScript value.
+
+### `broadcastChannel.ref()`
+<!-- YAML
+added: REPLACEME
+-->
+
+Opposite of `unref()`. Calling `ref()` on a previously `unref()`ed
+BroadcastChannel will *not* let the program exit if it's the only active handle
+left (the default behavior). If the port is `ref()`ed, calling `ref()` again
+will have no effect.
+
+### `broadcastChannel.unref()`
+<!-- YAML
+added: REPLACEME
+-->
+
+Calling `unref()` on a BroadcastChannel will allow the thread to exit if this
+is the only active handle in the event system. If the BroadcastChannel is
+already `unref()`ed calling `unref()` again will have no effect.
+
 ## Class: `MessageChannel`
 <!-- YAML
 added: v10.5.0

lib/internal/worker/io.js

@@ -19,11 +19,13 @@ const {
 const {
   MessagePort,
   MessageChannel,
+  broadcastChannel,
   drainMessagePort,
   moveMessagePortToContext,
   receiveMessageOnPort: receiveMessageOnPort_,
   stopMessagePort,
-  checkMessagePort
+  checkMessagePort,
+  DOMException,
 } = internalBinding('messaging');
 const {
   getEnvMessagePort
@@ -41,14 +43,20 @@ const {
 } = require('internal/event_target');
 const { inspect } = require('internal/util/inspect');
 const {
-  ERR_INVALID_ARG_TYPE
-} = require('internal/errors').codes;
+  codes: {
+    ERR_INVALID_ARG_TYPE,
+    ERR_MISSING_ARGS,
+  }
+} = require('internal/errors');
 
 const kData = Symbol('kData');
+const kHandle = Symbol('kHandle');
 const kIncrementsPortRef = Symbol('kIncrementsPortRef');
 const kLastEventId = Symbol('kLastEventId');
 const kName = Symbol('kName');
 const kOrigin = Symbol('kOrigin');
+const kOnMessage = Symbol('kOnMessage');
+const kOnMessageError = Symbol('kOnMessageError');
 const kPort = Symbol('kPort');
 const kPorts = Symbol('kPorts');
 const kWaitingStreams = Symbol('kWaitingStreams');
@@ -324,6 +332,76 @@ function receiveMessageOnPort(port) {
   return { message };
 }
 
+function onMessageEvent(type, data) {
+  this.dispatchEvent(new MessageEvent(type, { data }));
+}
+
+class BroadcastChannel extends EventTarget {
+  constructor(name) {
+    if (arguments.length === 0)
+      throw new ERR_MISSING_ARGS('name');
+    super();
+    this[kName] = `${name}`;
+    this[kHandle] = broadcastChannel(this[kName]);
+    this[kOnMessage] = onMessageEvent.bind(this, 'message');
+    this[kOnMessageError] = onMessageEvent.bind(this, 'messageerror');
+    this[kHandle].on('message', this[kOnMessage]);
+    this[kHandle].on('messageerror', this[kOnMessageError]);
+  }
+
+  [inspect.custom](depth, options) {
+    if (depth < 0)
+      return 'BroadcastChannel';
+
+    const opts = {
+      ...options,
+      depth: options.depth == null ? null : options.depth - 1
+    };
+
+    return `BroadcastChannel ${inspect({
+      name: this[kName],
+      active: this[kHandle] !== undefined,
+    }, opts)}`;
+  }
+
+  get name() { return this[kName]; }
+
+  close() {
+    if (this[kHandle] === undefined)
+      return;
+    this[kHandle].off('message', this[kOnMessage]);
+    this[kHandle].off('messageerror', this[kOnMessageError]);
+    this[kOnMessage] = undefined;
+    this[kOnMessageError] = undefined;
+    this[kHandle].close();
+    this[kHandle] = undefined;
+  }
+
+  postMessage(message) {
+    if (arguments.length === 0)
+      throw new ERR_MISSING_ARGS('message');
+    if (this[kHandle] === undefined)
+      throw new DOMException('BroadcastChannel is closed.');
+    if (this[kHandle].postMessage(message) === undefined)
+      throw new DOMException('Message could not be posted.');
+  }
+
+  ref() {
+    if (this[kHandle])
+      this[kHandle].ref();
+    return this;
+  }
+
+  unref() {
+    if (this[kHandle])
+      this[kHandle].unref();
+    return this;
+  }
+}
+
+defineEventHandler(BroadcastChannel.prototype, 'message');
+defineEventHandler(BroadcastChannel.prototype, 'messageerror');
+
 module.exports = {
   drainMessagePort,
   messageTypes,
@@ -339,5 +417,6 @@ module.exports = {
   setupPortReferencing,
   ReadableWorkerStdio,
   WritableWorkerStdio,
-  createWorkerStdio
+  createWorkerStdio,
+  BroadcastChannel,
 };

lib/worker_threads.js

@@ -13,6 +13,7 @@ const {
   MessageChannel,
   moveMessagePortToContext,
   receiveMessageOnPort,
+  BroadcastChannel,
 } = require('internal/worker/io');
 
 const {
@@ -32,4 +33,5 @@ module.exports = {
   Worker,
   parentPort: null,
   workerData: null,
+  BroadcastChannel,
 };