worker: implement Web Locks API

doc/api/worker_threads.md

@@ -274,6 +274,109 @@ if (isMainThread) {
 }
 ```
 
+## `worker.locks`
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+* {LockManager}
+
+An instance of a [`LockManager`][].
+
+### Class: `Lock`
+<!-- YAML
+added: REPLACEME
+-->
+
+The Lock interface provides the name and mode of a previously requested lock,
+which is received in the callback to [`locks.request()`][].
+
+#### `lock.name`
+<!-- YAML
+added: REPLACEME
+-->
+
+* {string}
+
+The name of this lock.
+
+#### `lock.mode`
+<!-- YAML
+added: REPLACEME
+-->
+
+* {string}
+
+The mode of this lock. Either `shared` or `exclusive`.
+
+### Class: `LockManager`
+<!-- YAML
+added: REPLACEME
+-->
+
+The `LockManager` interface provides methods for requesting a new [`Lock`][]
+object and querying for an existing `Lock` object. To get an instance of
+`LockManager`, call `worker_threads.locks`.
+
+This implementation matches the [browser `LockManager`][] API.
+
+#### `locks.request(name[, options], callback)`
+<!-- YAML
+added: REPLACEME
+-->
+
+* `name` {string}
+* `options` {Object}
+  * `mode` {string} Either `'exclusive'` or `'shared'`. **Default:**
+    `'exclusive'`.
+  * `ifAvailable` {boolean} If `true`, the lock request will only be
+    granted if it is not already held. If it cannot be granted, the
+    callback will be invoked with `null` instead of a `Lock` instance.
+    **Default:** `false`.
+  * `steal` {boolean} If `true`, then any held locks with the same name will be
+    released, and the request will be granted, preempting any queued requests
+    for it. **Default:** `false`.
+  * `signal` {AbortSignal} A signal that can be used to abort pending, not-yet
+    acquired lock requests.
+* `callback` {Function} The function to be invoked while the lock is acquired.
+  The lock will be released when the function ends, or if the function returns
+  a promise, when that promise settles.
+* Returns: {Promise}
+
+Requests a [`Lock`][] object with parameters specifying its name and
+characteristics.
+
+```js
+worker_threads.locks.request('my_resource', async (lock) => {
+  // The lock was granted.
+}).then(() => {
+  // The lock is released here.
+});
+```
+
+#### `locks.query()`
+<!-- YAML
+added: REPLACEME
+-->
+
+* Returns: {Promise}
+
+Returns a Promise that resolves with a [`LockManagerSnapshot`][] which contains
+information about held and pending locks.
+
+```js
+worker_threads.locks.query().then((state) => {
+  state.held.forEach((lock) => {
+    console.log(`held lock: name ${lock.name}, mode ${lock.mode}`);
+  });
+  state.pending.forEach((request) => {
+    console.log(`requested lock: name ${request.name}, mode ${request.mode}`);
+  });
+});
+```
+
 ## Class: `BroadcastChannel extends EventTarget`
 <!-- YAML
 added: v15.4.0
@@ -1086,6 +1189,9 @@ active handle in the event system. If the worker is already `unref()`ed calling
 [`EventTarget`]: https://developer.mozilla.org/en-US/docs/Web/API/EventTarget
 [`FileHandle`]: fs.md#fs_class_filehandle
 [`KeyObject`]: crypto.md#crypto_class_keyobject
+[`Lock`]: #worker_threads_class_lock
+[`LockManager`]: #worker_threads_class_lockmanager
+[`LockManagerSnapshot`]: https://developer.mozilla.org/en-US/docs/Web/API/LockManagerSnapshot
 [`MessagePort`]: #worker_threads_class_messageport
 [`SharedArrayBuffer`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer
 [`Uint8Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array
@@ -1095,6 +1201,7 @@ active handle in the event system. If the worker is already `unref()`ed calling
 [`data:` URL]: https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs
 [`fs.close()`]: fs.md#fs_fs_close_fd_callback
 [`fs.open()`]: fs.md#fs_fs_open_path_flags_mode_callback
+[`locks.request()`]: #worker_threads_locks_request_name_options_callback
 [`markAsUntransferable()`]: #worker_threads_worker_markasuntransferable_object
 [`perf_hooks.performance`]: perf_hooks.md#perf_hooks_perf_hooks_performance
 [`perf_hooks` `eventLoopUtilization()`]: perf_hooks.md#perf_hooks_performance_eventlooputilization_utilization1_utilization2
@@ -1126,6 +1233,7 @@ active handle in the event system. If the worker is already `unref()`ed calling
 [`worker.terminate()`]: #worker_threads_worker_terminate
 [`worker.threadId`]: #worker_threads_worker_threadid_1
 [async-resource-worker-pool]: async_hooks.md#async-resource-worker-pool
+[browser `LockManager`]: https://developer.mozilla.org/en-US/docs/Web/API/LockManager
 [browser `MessagePort`]: https://developer.mozilla.org/en-US/docs/Web/API/MessagePort
 [child processes]: child_process.md
 [contextified]: vm.md#vm_what_does_it_mean_to_contextify_an_object

lib/internal/worker.js

@@ -85,6 +85,7 @@ let debug = require('internal/util/debuglog').debuglog('worker', (fn) => {
 });
 
 let cwdCounter;
+let locksInitialized = false;
 
 if (isMainThread) {
   cwdCounter = new Uint32Array(new SharedArrayBuffer(4));
@@ -166,6 +167,13 @@ class Worker extends EventEmitter {
         options.env);
     }
 
+    if (isMainThread && !locksInitialized) {
+      locksInitialized = true;
+      // Make sure that locks are initialized before active
+      // multithreading starts.
+      require('worker_threads').locks.query();
+    }
+
     // Set up the C++ handle for the worker, as well as some internal wiring.
     this[kHandle] = new WorkerImpl(url,
                                    env === process.env ? null : env,

lib/internal/worker/io.js

@@ -348,7 +348,7 @@ class BroadcastChannel extends EventTarget {
       throw new ERR_MISSING_ARGS('name');
     super();
     this[kName] = `${name}`;
-    this[kHandle] = broadcastChannel(this[kName]);
+    this[kHandle] = broadcastChannel(`userland:${this[kName]}`);
     this[kOnMessage] = FunctionPrototypeBind(onMessageEvent, this, 'message');
     this[kOnMessageError] =
       FunctionPrototypeBind(onMessageEvent, this, 'messageerror');
@@ -412,6 +412,7 @@ defineEventHandler(BroadcastChannel.prototype, 'messageerror');
 module.exports = {
   drainMessagePort,
   messageTypes,
+  kHandle,
   kPort,
   kIncrementsPortRef,
   kWaitingStreams,