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‎doc/api/worker_threads.md‎
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‎lib/internal/worker/io.js‎
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‎lib/worker_threads.js‎
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‎test/parallel/test-worker-message-mark-as-uncloneable.js‎
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‎test/parallel/test-worker-message-mark-as-uncloneable.js‎
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@@ -194,6 +194,38 @@ isMarkedAsUntransferable(pooledBuffer);  // Returns true.
 
 There is no equivalent to this API in browsers.
 
+## `worker.markAsUncloneable(object)`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* `object` {any} Any arbitrary JavaScript value.
+
+Mark an object as not cloneable. If `object` is used as [`message`](#event-message) in
+a [`port.postMessage()`][] call, an error is thrown. This is a no-op if `object` is a
+primitive value.
+
+This has no effect on `ArrayBuffer`, or any `Buffer` like objects.
+
+This operation cannot be undone.
+
+```js
+const { markAsUncloneable } = require('node:worker_threads');
+
+const anyObject = { foo: 'bar' };
+markAsUncloneable(anyObject);
+const { port1 } = new MessageChannel();
+try {
+  // This will throw an error, because anyObject is not cloneable.
+  port1.postMessage(anyObject)
+} catch (error) {
+  // error.name === 'DataCloneError'
+}
+```
+
+There is no equivalent to this API in browsers.
+
 ## `worker.moveMessagePortToContext(port, contextifiedSandbox)`
 
 <!-- YAML
 
@@ -29,6 +29,14 @@ const {
   oninit: onInitSymbol,
   no_message_symbol: noMessageSymbol,
 } = internalBinding('symbols');
+const {
+  privateSymbols: {
+    transfer_mode_private_symbol,
+  },
+  constants: {
+    kCloneable,
+  },
+} = internalBinding('util');
 const {
   MessagePort,
   MessageChannel,
@@ -447,13 +455,21 @@ ObjectDefineProperties(BroadcastChannel.prototype, {
 defineEventHandler(BroadcastChannel.prototype, 'message');
 defineEventHandler(BroadcastChannel.prototype, 'messageerror');
 
+function markAsUncloneable(obj) {
+  if ((typeof obj !== 'object' && typeof obj !== 'function') || obj === null) {
+    return;
+  }
+  obj[transfer_mode_private_symbol] &= ~kCloneable;
+}
+
 module.exports = {
   drainMessagePort,
   messageTypes,
   kPort,
   kIncrementsPortRef,
   kWaitingStreams,
   kStdioWantsMoreDataCallback,
+  markAsUncloneable,
   moveMessagePortToContext,
   MessagePort,
   MessageChannel,
 
@@ -13,6 +13,7 @@ const {
 const {
   MessagePort,
   MessageChannel,
+  markAsUncloneable,
   moveMessagePortToContext,
   receiveMessageOnPort,
   BroadcastChannel,
@@ -31,6 +32,7 @@ module.exports = {
   isMainThread,
   MessagePort,
   MessageChannel,
+  markAsUncloneable,
   markAsUntransferable,
   isMarkedAsUntransferable,
   moveMessagePortToContext,
 
@@ -0,0 +1,70 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const { markAsUncloneable } = require('node:worker_threads');
+const { mustCall } = require('../common');
+
+const expectedErrorName = 'DataCloneError';
+
+// Uncloneables cannot be cloned during message posting
+{
+  const anyObject = { foo: 'bar' };
+  markAsUncloneable(anyObject);
+  const { port1 } = new MessageChannel();
+  assert.throws(() => port1.postMessage(anyObject), {
+    constructor: DOMException,
+    name: expectedErrorName,
+    code: 25,
+  }, `Should throw ${expectedErrorName} when posting uncloneables`);
+}
+
+// Uncloneables cannot be cloned during structured cloning
+{
+  class MockResponse extends Response {
+    constructor() {
+      super();
+      markAsUncloneable(this);
+    }
+  }
+  structuredClone(MockResponse.prototype);
+
+  markAsUncloneable(MockResponse.prototype);
+  const r = new MockResponse();
+  assert.throws(() => structuredClone(r), {
+    constructor: DOMException,
+    name: expectedErrorName,
+    code: 25,
+  }, `Should throw ${expectedErrorName} when cloning uncloneables`);
+}
+
+// markAsUncloneable cannot affect ArrayBuffer
+{
+  const pooledBuffer = new ArrayBuffer(8);
+  const { port1, port2 } = new MessageChannel();
+  markAsUncloneable(pooledBuffer);
+  port1.postMessage(pooledBuffer);
+  port2.on('message', mustCall((value) => {
+    assert.deepStrictEqual(value, pooledBuffer);
+    port2.close(mustCall());
+  }));
+}
+
+// markAsUncloneable can affect Node.js built-in object like Blob
+{
+  const cloneableBlob = new Blob();
+  const { port1, port2 } = new MessageChannel();
+  port1.postMessage(cloneableBlob);
+  port2.on('message', mustCall((value) => {
+    assert.deepStrictEqual(value, cloneableBlob);
+    port2.close(mustCall());
+  }));
+
+  const uncloneableBlob = new Blob();
+  markAsUncloneable(uncloneableBlob);
+  assert.throws(() => port1.postMessage(uncloneableBlob), {
+    constructor: DOMException,
+    name: expectedErrorName,
+    code: 25,
+  }, `Should throw ${expectedErrorName} when cloning uncloneables`);
+}