nodejs
diff --git a/‎doc/api/errors.md‎
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diff --git a/‎doc/api/process.md‎
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diff --git a/‎doc/api/worker_threads.md‎
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diff --git a/‎lib/internal/errors.js‎
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diff --git a/‎lib/internal/main/worker_thread.js‎
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diff --git a/‎lib/internal/worker.js‎
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@@ -3213,6 +3213,54 @@ 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_MESSAGING_ERRORED"></a>
+
+### `ERR_WORKER_MESSAGING_ERRORED`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1.1 - Active development
+
+The destination thread threw an error while processing a message sent via [`postMessageToThread()`][].
+
+<a id="ERR_WORKER_MESSAGING_FAILED"></a>
+
+### `ERR_WORKER_MESSAGING_FAILED`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1.1 - Active development
+
+The thread requested in [`postMessageToThread()`][] is invalid or has no `workerMessage` listener.
+
+<a id="ERR_WORKER_MESSAGING_SAME_THREAD"></a>
+
+### `ERR_WORKER_MESSAGING_SAME_THREAD`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1.1 - Active development
+
+The thread id requested in [`postMessageToThread()`][] is the current thread id.
+
+<a id="ERR_WORKER_MESSAGING_TIMEOUT"></a>
+
+### `ERR_WORKER_MESSAGING_TIMEOUT`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1.1 - Active development
+
+Sending a message via [`postMessageToThread()`][] timed out.
+
 <a id="ERR_WORKER_UNSERIALIZABLE_ERROR"></a>
 
 ### `ERR_WORKER_UNSERIALIZABLE_ERROR`
@@ -3954,6 +4002,7 @@ 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
+[`postMessageToThread()`]: worker_threads.md#workerpostmessagetothreadthreadid-value-transferlist-timeout
 [`process.on('exit')`]: process.md#event-exit
 [`process.send()`]: process.md#processsendmessage-sendhandle-options-callback
 [`process.setUncaughtExceptionCaptureCallback()`]: process.md#processsetuncaughtexceptioncapturecallbackfn
 
@@ -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 [`postMessageToThread()`][].
+* `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 [`postMessageToThread()`][].
+
 ### Event: `'uncaughtException'`
 
 <!-- YAML
@@ -4173,6 +4185,7 @@ cases:
 [`net.Server`]: net.md#class-netserver
 [`net.Socket`]: net.md#class-netsocket
 [`os.constants.dlopen`]: os.md#dlopen-constants
+[`postMessageToThread()`]: worker_threads.md#workerpostmessagetothreadthreadid-value-transferlist-timeout
 [`process.argv`]: #processargv
 [`process.config`]: #processconfig
 [`process.execPath`]: #processexecpath
 
@@ -220,6 +220,118 @@ if (isMainThread) {
 }
 ```
 
+## `worker.postMessageToThread(threadId, value[, transferList][, timeout])`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1.1 - Active development
+
+* `destination` {number} The target thread ID. If the thread ID is invalid, a
+  [`ERR_WORKER_MESSAGING_FAILED`][] error will be thrown. If the target thread ID is the current thread ID,
+  a [`ERR_WORKER_MESSAGING_SAME_THREAD`][] error will be thrown.
+* `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. If the operation times out,
+  a [`ERR_WORKER_MESSAGING_TIMEOUT`][] error is thrown.
+* Returns: {Promise} A promise which is fulfilled if the message was successfully processed by destination thread.
+
+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
+a [`ERR_WORKER_MESSAGING_FAILED`][] error.
+
+If the target thread threw an error while processing the `workerMessage` event, then the operation will throw
+a [`ERR_WORKER_MESSAGING_ERRORED`][] 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 `postMessageToThread`: 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,
+  postMessageToThread,
+  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} -> ${threadId}:`, value);
+    postMessageToThread(source, { message: 'pong' });
+  });
+} else if (level === 10) {
+  process.on('workerMessage', (value, source) => {
+    console.log(`${source} -> ${threadId}:`, value);
+    channel.postMessage('done');
+    channel.close();
+  });
+
+  await postMessageToThread(0, { message: 'ping' });
+}
+
+channel.onmessage = channel.close;
+```
+
+```cjs
+const { once } = require('node:events');
+const {
+  isMainThread,
+  postMessageToThread,
+  threadId,
+  workerData,
+  Worker,
+} = require('node:worker_threads');
+
+const channel = new BroadcastChannel('sync');
+const level = workerData?.level ?? 0;
+
+if (level < 10) {
+  const worker = new Worker(__filename, {
+    workerData: { level: level + 1 },
+  });
+}
+
+if (level === 0) {
+  process.on('workerMessage', (value, source) => {
+    console.log(`${source} -> ${threadId}:`, value);
+    postMessageToThread(source, { message: 'pong' });
+  });
+} else if (level === 10) {
+  process.on('workerMessage', (value, source) => {
+    console.log(`${source} -> ${threadId}:`, value);
+    channel.postMessage('done');
+    channel.close();
+  });
+
+  postMessageToThread(0, { message: 'ping' });
+}
+
+channel.onmessage = channel.close;
+```
+
 ## `worker.receiveMessageOnPort(port)`
 
 <!-- YAML
@@ -1361,6 +1473,10 @@ thread spawned will spawn another until the application crashes.
 [`Buffer.allocUnsafe()`]: buffer.md#static-method-bufferallocunsafesize
 [`Buffer`]: buffer.md
 [`ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST`]: errors.md#err_missing_message_port_in_transfer_list
+[`ERR_WORKER_MESSAGING_ERRORED`]: errors.md#err_worker_messaging_errored
+[`ERR_WORKER_MESSAGING_FAILED`]: errors.md#err_worker_messaging_failed
+[`ERR_WORKER_MESSAGING_SAME_THREAD`]: errors.md#err_worker_messaging_same_thread
+[`ERR_WORKER_MESSAGING_TIMEOUT`]: errors.md#err_worker_messaging_timeout
 [`ERR_WORKER_NOT_RUNNING`]: errors.md#err_worker_not_running
 [`EventTarget`]: https://developer.mozilla.org/en-US/docs/Web/API/EventTarget
 [`FileHandle`]: fs.md#class-filehandle
 
@@ -1911,6 +1911,10 @@ 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_MESSAGING_ERRORED', 'The destination thread threw an error while processing the message', Error);
+E('ERR_WORKER_MESSAGING_FAILED', 'Cannot find the destination thread or listener', Error);
+E('ERR_WORKER_MESSAGING_SAME_THREAD', 'Cannot sent a message to the same thread', Error);
+E('ERR_WORKER_MESSAGING_TIMEOUT', 'Sending a message to another thread timed out', 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);
 
@@ -44,6 +44,8 @@ const {
   kStdioWantsMoreDataCallback,
 } = workerIo;
 
+const { setupMainThreadPort } = require('internal/worker/messaging');
+
 const {
   onGlobalUncaughtException,
 } = require('internal/process/execution');
@@ -99,6 +101,7 @@ port.on('message', (message) => {
       manifestURL,
       publicPort,
       workerData,
+      mainThreadPort,
     } = message;
 
     if (doEval !== 'internal') {
@@ -112,6 +115,7 @@ port.on('message', (message) => {
     }
 
     require('internal/worker').assignEnvironmentData(environmentData);
+    setupMainThreadPort(mainThreadPort);
 
     if (SharedArrayBuffer !== undefined && Atomics !== undefined) {
       // The counter is only passed to the workers created by the main thread,
 
@@ -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');
@@ -251,14 +252,18 @@ 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));
     });
@@ -272,14 +277,15 @@ class Worker extends EventEmitter {
       cwdCounter: cwdCounter || workerIo.sharedCwdCounter,
       workerData: options.workerData,
       environmentData,
-      publicPort: port2,
       manifestURL: getOptionValue('--experimental-policy') ?
         require('internal/process/policy').url :
         null,
       manifestSrc: getOptionValue('--experimental-policy') ?
         require('internal/process/policy').src :
         null,
       hasStdin: !!options.stdin,
+      publicPort: publicPortToWorker,
+      mainThreadPort: mainThreadPortToWorker,
     }, transferList);
     // Use this to cache the Worker's loopStart value once available.
     this[kLoopStartTime] = -1;
@@ -302,6 +308,7 @@ 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();