worker: add postMessageToWorker

doc/api/errors.md

@@ -3085,6 +3085,16 @@ The `Worker` initialization failed.
 The `execArgv` option passed to the `Worker` constructor contains
 invalid flags.
 
+<a id="ERR_WORKER_INVALID_ID"></a>
+
+### `ERR_WORKER_INVALID_ID`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+The thread ID requested in [`postMessageToWorker()`][] is invalid or has no `workerMessage` listener.
+
 <a id="ERR_WORKER_NOT_RUNNING"></a>
 
 ### `ERR_WORKER_NOT_RUNNING`
@@ -3104,6 +3114,16 @@ The `Worker` instance terminated because it reached its memory limit.
 The path for the main script of a worker is neither an absolute path
 nor a relative path starting with `./` or `../`.
 
+<a id="ERR_WORKER_SAME_THREAD"></a>
+
+### `ERR_WORKER_SAME_THREAD`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+The thread id requested in [`postMessageToWorker()`][] is the current thread id.
+
 <a id="ERR_WORKER_UNSERIALIZABLE_ERROR"></a>
 
 ### `ERR_WORKER_UNSERIALIZABLE_ERROR`
@@ -4027,6 +4047,7 @@ An error occurred trying to allocate memory. This should never happen.
 [`new URLSearchParams(iterable)`]: url.md#new-urlsearchparamsiterable
 [`package.json`]: packages.md#nodejs-packagejson-field-definitions
 [`postMessage()`]: worker_threads.md#portpostmessagevalue-transferlist
+[`postMessageToWorker()`]: worker_threads.md#workerpostmessagetoworkerdestination-value-transferlist-timeout
 [`process.on('exit')`]: process.md#event-exit
 [`process.send()`]: process.md#processsendmessage-sendhandle-options-callback
 [`process.setUncaughtExceptionCaptureCallback()`]: process.md#processsetuncaughtexceptioncapturecallbackfn

doc/api/process.md

@@ -327,6 +327,18 @@ possible to record such errors in an error log, either periodically (which is
 likely best for long-running application) or upon process exit (which is likely
 most convenient for scripts).
 
+### Event: `'workerMessage'`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* `value` {any} A value transmitted using [`postMessageToWorker()`][].
+* `source` {number} The transmitting worker thread ID or `0` for the main thread.
+
+The `'workerMessage'` event is emitted for any incoming message send by the other
+party by using [`postMessageToWorker()`][].
+
 ### Event: `'uncaughtException'`
 
 <!-- YAML
@@ -4073,6 +4085,7 @@ cases:
 [`net.Server`]: net.md#class-netserver
 [`net.Socket`]: net.md#class-netsocket
 [`os.constants.dlopen`]: os.md#dlopen-constants
+[`postMessageToWorker()`]: worker_threads.md#workerpostmessagetoworkerdestination-value-transferlist-timeout
 [`process.argv`]: #processargv
 [`process.config`]: #processconfig
 [`process.execPath`]: #processexecpath

doc/api/worker_threads.md

@@ -252,6 +252,111 @@ if (isMainThread) {
 }
 ```
 
+## `worker.postMessageToWorker(destination, value[, transferList][, timeout])`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1.1 - Active development
+
+* `destination` {number} The target thread ID.
+* `value` {any} The value to send.
+* `transferList` {Object\[]} If one or more `MessagePort`-like objects are passed in `value`,
+  a `transferList` is required for those items or [`ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST`][] is thrown.
+  See [`port.postMessage()`][] for more information.
+* `timeout` {number} Time to wait for the message to be delivered in milliseconds.
+  By default it's `undefined`, which means wait forever.
+* Returns: {Promise} A promise which is fulfilled if the message was successfully sent.
+
+Sends a value to another worker, identified by its thread ID.
+
+If the target thread has no listener for the `workerMessage` event, then the operation will throw an error.
+
+This method should be used when the target thread is not the direct
+parent or child of the current thread.
+If the two threads are parent-children, use the [`require('node:worker_threads').parentPort.postMessage()`][]
+and the [`worker.postMessage()`][] to let the threads communicate.
+
+The example below shows the use of of `postMessageToWorker`: it creates 10 nested threads,
+the last one will try to communicate with the main thread.
+
+```mjs
+import { fileURLToPath } from 'node:url';
+import { once } from 'node:events';
+import process from 'node:process';
+import {
+  isMainThread,
+  postMessageToWorker,
+  threadId,
+  workerData,
+  Worker,
+} from 'node:worker_threads';
+
+const channel = new BroadcastChannel('sync');
+const level = workerData?.level ?? 0;
+
+if (level < 10) {
+  const worker = new Worker(fileURLToPath(import.meta.url), {
+    workerData: { level: level + 1 },
+  });
+}
+
+if (level === 0) {
+  process.on('workerMessage', (value, source) => {
+    console.log(`${source} -> ${threadId}:`, value);
+    postMessageToWorker(source, { message: 'pong' });
+  });
+} else if (level === 10) {
+  process.on('workerMessage', (value, source) => {
+    console.log(`${source} -> ${threadId}:`, value);
+    channel.postMessage('done');
+    channel.close();
+  });
+
+  await postMessageToWorker(0, { message: 'ping' });
+}
+
+channel.onmessage = channel.close;
+```
+
+```cjs
+const { once } = require('node:events');
+const {
+  isMainThread,
+  postMessageToWorker,
+  threadId,
+  workerData,
+  Worker,
+} = require('node:worker_threads');
+
+const channel = new BroadcastChannel('sync');
+const level = workerData?.level ?? 0;
+
+if (level < 10) {
+  const worker = new Worker(__filename, {
+    workerData: { level: level + 1 },
+  });
+}
+
+if (level === 0) {
+  process.on('workerMessage', (value, source) => {
+    console.log(`${source} -> ${threadId}:`, value);
+    postMessageToWorker(source, { message: 'pong' });
+  });
+} else if (level === 10) {
+  process.on('workerMessage', (value, source) => {
+    console.log(`${source} -> ${threadId}:`, value);
+    channel.postMessage('done');
+    channel.close();
+  });
+
+  postMessageToWorker(0, { message: 'ping' });
+}
+
+channel.onmessage = channel.close;
+```
+
 ## `worker.receiveMessageOnPort(port)`
 
 <!-- YAML

lib/internal/errors.js

@@ -1862,6 +1862,7 @@ E('ERR_WORKER_INIT_FAILED', 'Worker initialization failure: %s', Error);
 E('ERR_WORKER_INVALID_EXEC_ARGV', (errors, msg = 'invalid execArgv flags') =>
   `Initiated Worker with ${msg}: ${ArrayPrototypeJoin(errors, ', ')}`,
   Error);
+E('ERR_WORKER_INVALID_ID', 'Invalid worker id %d', Error);
 E('ERR_WORKER_NOT_RUNNING', 'Worker instance not running', Error);
 E('ERR_WORKER_OUT_OF_MEMORY',
   'Worker terminated due to reaching memory limit: %s', Error);
@@ -1876,6 +1877,7 @@ E('ERR_WORKER_PATH', (filename) =>
   ) +
   ` Received "${filename}"`,
   TypeError);
+E('ERR_WORKER_SAME_THREAD', 'Cannot connect to the same thread', Error);
 E('ERR_WORKER_UNSERIALIZABLE_ERROR',
   'Serializing an uncaught exception failed', Error);
 E('ERR_WORKER_UNSUPPORTED_OPERATION',

lib/internal/main/worker_thread.js

@@ -44,6 +44,8 @@ const {
   kStdioWantsMoreDataCallback,
 } = workerIo;
 
+const { setupMainThreadPort } = require('internal/worker/messaging');
+
 const {
   onGlobalUncaughtException,
 } = require('internal/process/execution');
@@ -96,6 +98,7 @@ port.on('message', (message) => {
       hasStdin,
       publicPort,
       workerData,
+      mainThreadPort,
     } = message;
 
     if (doEval !== 'internal') {
@@ -109,6 +112,7 @@ port.on('message', (message) => {
     }
 
     require('internal/worker').assignEnvironmentData(environmentData);
+    setupMainThreadPort(mainThreadPort);
 
     if (SharedArrayBuffer !== undefined) {
       // The counter is only passed to the workers created by the main thread,

lib/internal/worker.js

@@ -56,6 +56,7 @@ const {
   ReadableWorkerStdio,
   WritableWorkerStdio,
 } = workerIo;
+const { createMainThreadPort, destroyMainThreadPort } = require('internal/worker/messaging');
 const { deserializeError } = require('internal/error_serdes');
 const { fileURLToPath, isURL, pathToFileURL } = require('internal/url');
 const { kEmptyObject } = require('internal/util');
@@ -250,14 +251,18 @@ class Worker extends EventEmitter {
 
     this[kParentSideStdio] = { stdin, stdout, stderr };
 
-    const { port1, port2 } = new MessageChannel();
-    const transferList = [port2];
+    const mainThreadPortToWorker = createMainThreadPort(this.threadId);
+    const {
+      port1: publicPortToParent,
+      port2: publicPortToWorker,
+    } = new MessageChannel();
+    const transferList = [mainThreadPortToWorker, publicPortToWorker];
     // If transferList is provided.
     if (options.transferList)
       ArrayPrototypePush(transferList,
                          ...new SafeArrayIterator(options.transferList));
 
-    this[kPublicPort] = port1;
+    this[kPublicPort] = publicPortToParent;
     ArrayPrototypeForEach(['message', 'messageerror'], (event) => {
       this[kPublicPort].on(event, (message) => this.emit(event, message));
     });
@@ -271,8 +276,9 @@ class Worker extends EventEmitter {
       cwdCounter: cwdCounter || workerIo.sharedCwdCounter,
       workerData: options.workerData,
       environmentData,
-      publicPort: port2,
       hasStdin: !!options.stdin,
+      publicPort: publicPortToWorker,
+      mainThreadPort: mainThreadPortToWorker,
     }, transferList);
     // Use this to cache the Worker's loopStart value once available.
     this[kLoopStartTime] = -1;
@@ -295,6 +301,7 @@ class Worker extends EventEmitter {
     debug(`[${threadId}] hears end event for Worker ${this.threadId}`);
     drainMessagePort(this[kPublicPort]);
     drainMessagePort(this[kPort]);
+    destroyMainThreadPort(this.threadId);
     this.removeAllListeners('message');
     this.removeAllListeners('messageerrors');
     this[kPublicPort].unref();