From 4667b07cd2d6eb0295d6cd1f40163ef14ce538b0 Mon Sep 17 00:00:00 2001
From: Jacob Smith <3012099+JakobJingleheimer@users.noreply.github.com>
Date: Thu, 13 Apr 2023 09:35:17 +0200
Subject: [PATCH] esm: move hook execution to separate thread
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

PR-URL: https://github.com/nodejs/node/pull/44710
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Geoffrey Booth <webadmin@geoffreybooth.com>
Co-authored-by: Antoine du Hamel <duhamelantoine1995@gmail.com>
Co-authored-by: Geoffrey Booth <webadmin@geoffreybooth.com>
Co-authored-by: Michaël Zasso <targos@protonmail.com>
---
 doc/api/esm.md                                |  39 +-
 lib/internal/main/worker_thread.js            |  89 +++--
 lib/internal/modules/esm/hooks.js             | 349 ++++++++++++------
 .../modules/esm/initialize_import_meta.js     |  51 ++-
 lib/internal/modules/esm/loader.js            | 212 +++++++----
 lib/internal/modules/esm/module_job.js        |   7 +-
 lib/internal/modules/esm/resolve.js           |  23 +-
 lib/internal/modules/esm/shared_constants.js  |  25 ++
 lib/internal/modules/esm/utils.js             |  69 +++-
 lib/internal/modules/esm/worker.js            | 210 +++++++++++
 lib/internal/process/esm_loader.js            | 133 ++-----
 lib/internal/worker.js                        |  34 +-
 src/node_worker.cc                            |  12 +-
 .../test-esm-import-meta-resolve.mjs          |  56 ++-
 test/es-module/test-esm-loader-modulemap.js   |   4 +-
 test/es-module/test-esm-loader-search.js      |   4 +-
 .../test-esm-loader-with-syntax-error.mjs     |   2 +-
 test/es-module/test-esm-resolve-type.mjs      |  20 +-
 .../es-module-loaders/hooks-input.mjs         |  15 +-
 .../es-module-loaders/loader-edge-cases.mjs   |   6 +-
 .../loader-load-foo-or-42.mjs                 |   2 +-
 .../loader-load-incomplete.mjs                |   2 +-
 .../loader-load-passthru.mjs                  |   7 +-
 ...loader-load-receiving-modified-context.mjs |   5 +-
 .../es-module-loaders/loader-log-args.mjs     |  15 +-
 .../es-module-loaders/loader-resolve-42.mjs   |   9 +-
 .../es-module-loaders/loader-resolve-foo.mjs  |   7 +-
 .../loader-resolve-incomplete.mjs             |   2 +-
 .../loader-resolve-next-modified.mjs          |   2 +-
 .../loader-resolve-passthru.mjs               |   7 +-
 ...der-resolve-receiving-modified-context.mjs |   5 +-
 .../loader-resolve-shortcircuit.mjs           |   2 +-
 .../loader-resolve-strip-xxx.mjs              |   8 +-
 .../loader-resolve-strip-yyy.mjs              |   5 +-
 .../import.meta.never-resolve.mjs             |   2 +-
 .../es-modules/import-resolve-exports.mjs     |  10 +-
 test/fixtures/es-modules/runmain.mjs          |   4 +-
 37 files changed, 997 insertions(+), 457 deletions(-)
 create mode 100644 lib/internal/modules/esm/shared_constants.js
 create mode 100644 lib/internal/modules/esm/worker.js

diff --git a/doc/api/esm.md b/doc/api/esm.md
index 6293779131e4e0..884c3e83c9e684 100644
--- a/doc/api/esm.md
+++ b/doc/api/esm.md
@@ -7,6 +7,9 @@
 <!-- YAML
 added: v8.5.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/44710
+    description: Loader hooks are executed off the main thread.
   - version:
     - v18.6.0
     - v16.17.0
@@ -325,6 +328,9 @@ added:
   - v13.9.0
   - v12.16.2
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/44710
+    description: This API now returns a string synchronously instead of a Promise.
   - version:
       - v16.2.0
       - v14.18.0
@@ -340,29 +346,26 @@ command flag enabled.
 * `specifier` {string} The module specifier to resolve relative to `parent`.
 * `parent` {string|URL} The absolute parent module URL to resolve from. If none
   is specified, the value of `import.meta.url` is used as the default.
-* Returns: {Promise}
+* Returns: {string}
 
 Provides a module-relative resolution function scoped to each module, returning
-the URL string.
+the URL string. In alignment with browser behavior, this now returns
+synchronously.
 
-<!-- eslint-skip -->
+> **Caveat** This can result in synchronous file-system operations, which
+> can impact performance similarly to `require.resolve`.
 
 ```js
-const dependencyAsset = await import.meta.resolve('component-lib/asset.css');
+const dependencyAsset = import.meta.resolve('component-lib/asset.css');
 ```
 
 `import.meta.resolve` also accepts a second argument which is the parent module
-from which to resolve from:
-
-<!-- eslint-skip -->
+from which to resolve:
 
 ```js
-await import.meta.resolve('./dep', import.meta.url);
+import.meta.resolve('./dep', import.meta.url);
 ```
 
-This function is asynchronous because the ES module resolver in Node.js is
-allowed to be asynchronous.
-
 ## Interoperability with CommonJS
 
 ### `import` statements
@@ -730,6 +733,11 @@ A hook that returns without calling `next<hookName>()` _and_ without returning
 `shortCircuit: true` also triggers an exception. These errors are to help
 prevent unintentional breaks in the chain.
 
+Hooks are run in a separate thread, isolated from the main. That means it is a
+different [realm](https://tc39.es/ecma262/#realm). The hooks thread may be
+terminated by the main thread at any time, so do not depend on asynchronous
+operations to (like `console.log`) complete.
+
 #### `resolve(specifier, context, nextResolve)`
 
 <!-- YAML
@@ -762,7 +770,7 @@ changes:
   Node.js default `resolve` hook after the last user-supplied `resolve` hook
   * `specifier` {string}
   * `context` {Object}
-* Returns: {Object}
+* Returns: {Object|Promise}
   * `format` {string|null|undefined} A hint to the load hook (it might be
     ignored)
     `'builtin' | 'commonjs' | 'json' | 'module' | 'wasm'`
@@ -772,6 +780,9 @@ changes:
     terminate the chain of `resolve` hooks. **Default:** `false`
   * `url` {string} The absolute URL to which this input resolves
 
+> **Caveat** Despite support for returning promises and async functions, calls
+> to `resolve` may block the main thread which can impact performance.
+
 The `resolve` hook chain is responsible for telling Node.js where to find and
 how to cache a given `import` statement or expression. It can optionally return
 its format (such as `'module'`) as a hint to the `load` hook. If a format is
@@ -797,7 +808,7 @@ Node.js module specifier resolution behavior_ when calling `defaultResolve`, the
 `context.conditions` array originally passed into the `resolve` hook.
 
 ```js
-export async function resolve(specifier, context, nextResolve) {
+export function resolve(specifier, context, nextResolve) {
   const { parentURL = null } = context;
 
   if (Math.random() > 0.5) { // Some condition.
@@ -1100,7 +1111,7 @@ const baseURL = pathToFileURL(`${cwd()}/`).href;
 // CoffeeScript files end in .coffee, .litcoffee, or .coffee.md.
 const extensionsRegex = /\.coffee$|\.litcoffee$|\.coffee\.md$/;
 
-export async function resolve(specifier, context, nextResolve) {
+export function resolve(specifier, context, nextResolve) {
   if (extensionsRegex.test(specifier)) {
     const { parentURL = baseURL } = context;
 
diff --git a/lib/internal/main/worker_thread.js b/lib/internal/main/worker_thread.js
index 2ebfb849663eb6..4d8938e58bdf33 100644
--- a/lib/internal/main/worker_thread.js
+++ b/lib/internal/main/worker_thread.js
@@ -10,6 +10,7 @@ const {
   ObjectDefineProperty,
   PromisePrototypeThen,
   RegExpPrototypeExec,
+  SafeWeakMap,
   globalThis: {
     Atomics,
     SharedArrayBuffer,
@@ -89,23 +90,25 @@ port.on('message', (message) => {
     const {
       argv,
       cwdCounter,
-      filename,
       doEval,
-      workerData,
       environmentData,
-      publicPort,
+      filename,
+      hasStdin,
       manifestSrc,
       manifestURL,
-      hasStdin,
+      publicPort,
+      workerData,
     } = message;
 
-    if (argv !== undefined) {
-      ArrayPrototypePushApply(process.argv, argv);
-    }
+    if (doEval !== 'internal') {
+      if (argv !== undefined) {
+        ArrayPrototypePushApply(process.argv, argv);
+      }
 
-    const publicWorker = require('worker_threads');
-    publicWorker.parentPort = publicPort;
-    publicWorker.workerData = workerData;
+      const publicWorker = require('worker_threads');
+      publicWorker.parentPort = publicPort;
+      publicWorker.workerData = workerData;
+    }
 
     require('internal/worker').assignEnvironmentData(environmentData);
 
@@ -138,31 +141,47 @@ port.on('message', (message) => {
     debug(`[${threadId}] starts worker script ${filename} ` +
           `(eval = ${doEval}) at cwd = ${process.cwd()}`);
     port.postMessage({ type: UP_AND_RUNNING });
-    if (doEval === 'classic') {
-      const { evalScript } = require('internal/process/execution');
-      const name = '[worker eval]';
-      // This is necessary for CJS module compilation.
-      // TODO: pass this with something really internal.
-      ObjectDefineProperty(process, '_eval', {
-        __proto__: null,
-        configurable: true,
-        enumerable: true,
-        value: filename,
-      });
-      ArrayPrototypeSplice(process.argv, 1, 0, name);
-      evalScript(name, filename);
-    } else if (doEval === 'module') {
-      const { evalModule } = require('internal/process/execution');
-      PromisePrototypeThen(evalModule(filename), undefined, (e) => {
-        workerOnGlobalUncaughtException(e, true);
-      });
-    } else {
-      // script filename
-      // runMain here might be monkey-patched by users in --require.
-      // XXX: the monkey-patchability here should probably be deprecated.
-      ArrayPrototypeSplice(process.argv, 1, 0, filename);
-      const CJSLoader = require('internal/modules/cjs/loader');
-      CJSLoader.Module.runMain(filename);
+    switch (doEval) {
+      case 'internal': {
+        // Create this WeakMap in js-land because V8 has no C++ API for WeakMap.
+        internalBinding('module_wrap').callbackMap = new SafeWeakMap();
+        require(filename)(workerData, publicPort);
+        break;
+      }
+
+      case 'classic': {
+        const { evalScript } = require('internal/process/execution');
+        const name = '[worker eval]';
+        // This is necessary for CJS module compilation.
+        // TODO: pass this with something really internal.
+        ObjectDefineProperty(process, '_eval', {
+          __proto__: null,
+          configurable: true,
+          enumerable: true,
+          value: filename,
+        });
+        ArrayPrototypeSplice(process.argv, 1, 0, name);
+        evalScript(name, filename);
+        break;
+      }
+
+      case 'module': {
+        const { evalModule } = require('internal/process/execution');
+        PromisePrototypeThen(evalModule(filename), undefined, (e) => {
+          workerOnGlobalUncaughtException(e, true);
+        });
+        break;
+      }
+
+      default: {
+        // script filename
+        // runMain here might be monkey-patched by users in --require.
+        // XXX: the monkey-patchability here should probably be deprecated.
+        ArrayPrototypeSplice(process.argv, 1, 0, filename);
+        const CJSLoader = require('internal/modules/cjs/loader');
+        CJSLoader.Module.runMain(filename);
+        break;
+      }
     }
   } else if (message.type === STDIO_PAYLOAD) {
     const { stream, chunks } = message;
diff --git a/lib/internal/modules/esm/hooks.js b/lib/internal/modules/esm/hooks.js
index 513204bb9d7e48..7df6672582c50d 100644
--- a/lib/internal/modules/esm/hooks.js
+++ b/lib/internal/modules/esm/hooks.js
@@ -4,9 +4,11 @@ const {
   ArrayPrototypeJoin,
   ArrayPrototypePush,
   FunctionPrototypeCall,
+  Int32Array,
   ObjectAssign,
   ObjectDefineProperty,
   ObjectSetPrototypeOf,
+  Promise,
   SafeSet,
   StringPrototypeSlice,
   StringPrototypeToUpperCase,
@@ -14,14 +16,26 @@ const {
 } = primordials;
 
 const {
-  ERR_LOADER_CHAIN_INCOMPLETE,
+  Atomics: {
+    load: AtomicsLoad,
+    wait: AtomicsWait,
+    waitAsync: AtomicsWaitAsync,
+  },
+  SharedArrayBuffer,
+} = globalThis;
+
+const {
   ERR_INTERNAL_ASSERTION,
   ERR_INVALID_ARG_TYPE,
   ERR_INVALID_ARG_VALUE,
   ERR_INVALID_RETURN_PROPERTY_VALUE,
   ERR_INVALID_RETURN_VALUE,
+  ERR_LOADER_CHAIN_INCOMPLETE,
+  ERR_WORKER_UNSERIALIZABLE_ERROR,
 } = require('internal/errors').codes;
-const { isURL, URL } = require('internal/url');
+const { exitCodes: { kUnfinishedTopLevelAwait } } = internalBinding('errors');
+const { URL } = require('internal/url');
+const { receiveMessageOnPort } = require('worker_threads');
 const {
   isAnyArrayBuffer,
   isArrayBufferView,
@@ -33,10 +47,19 @@ const {
 
 const {
   defaultResolve,
+  throwIfInvalidParentURL,
 } = require('internal/modules/esm/resolve');
 const {
   getDefaultConditions,
 } = require('internal/modules/esm/utils');
+const { deserializeError } = require('internal/error_serdes');
+const {
+  SHARED_MEMORY_BYTE_LENGTH,
+  WORKER_TO_MAIN_THREAD_NOTIFICATION,
+} = require('internal/modules/esm/shared_constants');
+let debug = require('internal/util/debuglog').debuglog('esm', (fn) => {
+  debug = fn;
+});
 
 
 /**
@@ -49,7 +72,7 @@ const {
 
 
 class Hooks {
-  #hooks = {
+  #chains = {
     /**
      * Prior to ESM loading. These are called once before any modules are started.
      * @private
@@ -83,27 +106,20 @@ class Hooks {
     ],
   };
 
-  // Enable an optimization in ESMLoader.getModuleJob
-  hasCustomResolveOrLoadHooks = false;
-
   // Cache URLs we've already validated to avoid repeated validation
   #validatedUrls = new SafeSet();
 
-  #importMetaInitializer = require('internal/modules/esm/initialize_import_meta').initializeImportMeta;
-
   constructor(userLoaders) {
-    this.#addCustomLoaders(userLoaders);
+    this.addCustomLoaders(userLoaders);
   }
 
   /**
    * Collect custom/user-defined module loader hook(s).
    * After all hooks have been collected, the global preload hook(s) must be initialized.
    * @param {import('./loader.js).KeyedExports} customLoaders Exports from user-defined loaders
-   *  (as returned by `ESMLoader.import()`).
+   *  (as returned by `ModuleLoader.import()`).
    */
-  #addCustomLoaders(
-    customLoaders = [],
-  ) {
+  addCustomLoaders(customLoaders = []) {
     for (let i = 0; i < customLoaders.length; i++) {
       const {
         exports,
@@ -116,33 +132,13 @@ class Hooks {
       } = pluckHooks(exports);
 
       if (globalPreload) {
-        ArrayPrototypePush(
-          this.#hooks.globalPreload,
-          {
-            fn: globalPreload,
-            url,
-          },
-        );
+        ArrayPrototypePush(this.#chains.globalPreload, { fn: globalPreload, url });
       }
       if (resolve) {
-        this.hasCustomResolveOrLoadHooks = true;
-        ArrayPrototypePush(
-          this.#hooks.resolve,
-          {
-            fn: resolve,
-            url,
-          },
-        );
+        ArrayPrototypePush(this.#chains.resolve, { fn: resolve, url });
       }
       if (load) {
-        this.hasCustomResolveOrLoadHooks = true;
-        ArrayPrototypePush(
-          this.#hooks.load,
-          {
-            fn: load,
-            url,
-          },
-        );
+        ArrayPrototypePush(this.#chains.load, { fn: load, url });
       }
     }
   }
@@ -150,8 +146,9 @@ class Hooks {
   /**
    * Initialize `globalPreload` hooks.
    */
-  preload() {
-    for (let i = this.#hooks.globalPreload.length - 1; i >= 0; i--) {
+  initializeGlobalPreload() {
+    const preloadScripts = [];
+    for (let i = this.#chains.globalPreload.length - 1; i >= 0; i--) {
       const { MessageChannel } = require('internal/worker/io');
       const channel = new MessageChannel();
       const {
@@ -165,7 +162,7 @@ class Hooks {
       const {
         fn: preload,
         url: specifier,
-      } = this.#hooks.globalPreload[i];
+      } = this.#chains.globalPreload[i];
 
       const preloaded = preload({
         port: insideLoader,
@@ -173,69 +170,20 @@ class Hooks {
 
       if (preloaded == null) { return; }
 
-      const hookErrIdentifier = `${specifier} globalPreload`;
-
       if (typeof preloaded !== 'string') { // [2]
         throw new ERR_INVALID_RETURN_VALUE(
           'a string',
-          hookErrIdentifier,
+          `${specifier} globalPreload`,
           preload,
         );
       }
-      const { compileFunction } = require('vm');
-      const preloadInit = compileFunction(
-        preloaded,
-        ['getBuiltin', 'port', 'setImportMetaCallback'],
-        {
-          filename: '<preload>',
-        },
-      );
-      const { BuiltinModule } = require('internal/bootstrap/realm');
-      // We only allow replacing the importMetaInitializer during preload;
-      // after preload is finished, we disable the ability to replace it.
-      //
-      // This exposes accidentally setting the initializer too late by throwing an error.
-      let finished = false;
-      let replacedImportMetaInitializer = false;
-      let next = this.#importMetaInitializer;
-      try {
-        // Calls the compiled preload source text gotten from the hook
-        // Since the parameters are named we use positional parameters
-        // see compileFunction above to cross reference the names
-        FunctionPrototypeCall(
-          preloadInit,
-          globalThis,
-          // Param getBuiltin
-          (builtinName) => {
-            if (BuiltinModule.canBeRequiredWithoutScheme(builtinName)) {
-              return require(builtinName);
-            }
-            throw new ERR_INVALID_ARG_VALUE('builtinName', builtinName);
-          },
-          // Param port
-          insidePreload,
-          // Param setImportMetaCallback
-          (fn) => {
-            if (finished || typeof fn !== 'function') {
-              throw new ERR_INVALID_ARG_TYPE('fn', fn);
-            }
-            replacedImportMetaInitializer = true;
-            const parent = next;
-            next = (meta, context) => {
-              return fn(meta, context, parent);
-            };
-          });
-      } finally {
-        finished = true;
-        if (replacedImportMetaInitializer) {
-          this.#importMetaInitializer = next;
-        }
-      }
-    }
-  }
 
-  importMetaInitialize(meta, context) {
-    this.#importMetaInitializer(meta, context);
+      ArrayPrototypePush(preloadScripts, {
+        code: preloaded,
+        port: insidePreload,
+      });
+    }
+    return preloadScripts;
   }
 
   /**
@@ -257,20 +205,9 @@ class Hooks {
     parentURL,
     importAssertions = { __proto__: null },
   ) {
-    const isMain = parentURL === undefined;
+    throwIfInvalidParentURL(parentURL);
 
-    if (
-      !isMain &&
-      typeof parentURL !== 'string' &&
-      !isURL(parentURL)
-    ) {
-      throw new ERR_INVALID_ARG_TYPE(
-        'parentURL',
-        ['string', 'URL'],
-        parentURL,
-      );
-    }
-    const chain = this.#hooks.resolve;
+    const chain = this.#chains.resolve;
     const context = {
       conditions: getDefaultConditions(),
       importAssertions,
@@ -392,7 +329,7 @@ class Hooks {
    * @returns {Promise<{ format: ModuleFormat, source: ModuleSource }>}
    */
   async load(url, context = {}) {
-    const chain = this.#hooks.load;
+    const chain = this.#chains.load;
     const meta = {
       chainFinished: null,
       context,
@@ -515,9 +452,200 @@ class Hooks {
     };
   }
 }
-
 ObjectSetPrototypeOf(Hooks.prototype, null);
 
+/**
+ * There may be multiple instances of Hooks/HooksProxy, but there is only 1 Internal worker, so
+ * there is only 1 MessageChannel.
+ */
+let MessageChannel;
+class HooksProxy {
+  /**
+   * Shared memory. Always use Atomics method to read or write to it.
+   * @type {Int32Array}
+   */
+  #lock;
+  /**
+   * The InternalWorker instance, which lets us communicate with the loader thread.
+   */
+  #worker;
+
+  /**
+   * The last notification ID received from the worker. This is used to detect
+   * if the worker has already sent a notification before putting the main
+   * thread to sleep, to avoid a race condition.
+   * @type {number}
+   */
+  #workerNotificationLastId = 0;
+
+  /**
+   * Track how many async responses the main thread should expect.
+   * @type {number}
+   */
+  #numberOfPendingAsyncResponses = 0;
+
+  #isReady = false;
+
+  constructor() {
+    const { InternalWorker } = require('internal/worker');
+    MessageChannel ??= require('internal/worker/io').MessageChannel;
+
+    const lock = new SharedArrayBuffer(SHARED_MEMORY_BYTE_LENGTH);
+    this.#lock = new Int32Array(lock);
+
+    this.#worker = new InternalWorker('internal/modules/esm/worker', {
+      stderr: false,
+      stdin: false,
+      stdout: false,
+      trackUnmanagedFds: false,
+      workerData: {
+        lock,
+      },
+    });
+    this.#worker.unref(); // ! Allows the process to eventually exit.
+  }
+
+  #waitForWorker() {
+    if (!this.#isReady) {
+      const { kIsOnline } = require('internal/worker');
+      if (!this.#worker[kIsOnline]) {
+        debug('wait for signal from worker');
+        AtomicsWait(this.#lock, WORKER_TO_MAIN_THREAD_NOTIFICATION, 0);
+        const response = this.#worker.receiveMessageSync();
+        const { preloadScripts } = this.#unwrapMessage(response);
+        this.#executePreloadScripts(preloadScripts);
+      }
+
+      this.#isReady = true;
+    }
+  }
+
+  #beforeExitHandler = () => {
+    debug('beforeExit main thread', this.#lock, this.#numberOfPendingAsyncResponses);
+    if (this.#numberOfPendingAsyncResponses !== 0) {
+      // The worker still has some work to do, let's wait for it before terminating the process.
+      this.#worker.ref();
+    }
+  };
+
+  async makeAsyncRequest(method, ...args) {
+    this.#waitForWorker();
+
+    MessageChannel ??= require('internal/worker/io').MessageChannel;
+    const asyncCommChannel = new MessageChannel();
+
+    // Pass work to the worker.
+    debug('post async message to worker', { method, args });
+    this.#worker.postMessage({ method, args, port: asyncCommChannel.port2 }, [asyncCommChannel.port2]);
+
+    if (this.#numberOfPendingAsyncResponses++ === 0) {
+      // On the next lines, the main thread will await a response from the worker thread that might
+      // come AFTER the last task in the event loop has run its course and there would be nothing
+      // left keeping the thread alive (and once the main thread dies, the whole process stops).
+      // However we want to keep the process alive until the worker thread responds (or until the
+      // event loop of the worker thread is also empty). So we add the beforeExit handler whose
+      // mission is to lock the main thread until we hear back from the worker thread. The `if`
+      // condition is there so we only add the event handler once (if there are already pending
+      // async responses, the previous calls have added the event listener).
+      process.on('beforeExit', this.#beforeExitHandler);
+    }
+
+    let response;
+    do {
+      debug('wait for async response from worker', { method, args });
+      await AtomicsWaitAsync(this.#lock, WORKER_TO_MAIN_THREAD_NOTIFICATION, this.#workerNotificationLastId).value;
+      this.#workerNotificationLastId = AtomicsLoad(this.#lock, WORKER_TO_MAIN_THREAD_NOTIFICATION);
+
+      // In case the beforeExit handler was called during the await, we revert its actions.
+      this.#worker.unref();
+
+      response = receiveMessageOnPort(asyncCommChannel.port1);
+    } while (response == null);
+    debug('got async response from worker', { method, args }, this.#lock);
+
+    if (--this.#numberOfPendingAsyncResponses === 0) {
+      // We got all the responses from the worker, its job is done (until next time).
+      process.off('beforeExit', this.#beforeExitHandler);
+    }
+
+    const body = this.#unwrapMessage(response);
+    asyncCommChannel.port1.close();
+    return body;
+  }
+
+  makeSyncRequest(method, ...args) {
+    this.#waitForWorker();
+
+    // Pass work to the worker.
+    debug('post sync message to worker', { method, args });
+    this.#worker.postMessage({ method, args });
+
+    let response;
+    do {
+      debug('wait for sync response from worker', { method, args });
+      // Sleep until worker responds.
+      AtomicsWait(this.#lock, WORKER_TO_MAIN_THREAD_NOTIFICATION, this.#workerNotificationLastId);
+      this.#workerNotificationLastId = AtomicsLoad(this.#lock, WORKER_TO_MAIN_THREAD_NOTIFICATION);
+
+      response = this.#worker.receiveMessageSync();
+    } while (response == null);
+    debug('got sync response from worker', { method, args });
+    if (response.message.status === 'never-settle') {
+      process.exit(kUnfinishedTopLevelAwait);
+    }
+    return this.#unwrapMessage(response);
+  }
+
+  #unwrapMessage(response) {
+    if (response.message.status === 'never-settle') {
+      return new Promise(() => {});
+    }
+    if (response.message.status === 'error') {
+      if (response.message.body == null) throw response.message.body;
+      if (response.message.body.serializationFailed || response.message.body.serialized == null) {
+        throw ERR_WORKER_UNSERIALIZABLE_ERROR();
+      }
+
+      // eslint-disable-next-line no-restricted-syntax
+      throw deserializeError(response.message.body.serialized);
+    } else {
+      return response.message.body;
+    }
+  }
+
+  #executePreloadScripts(preloadScripts) {
+    for (let i = 0; i < preloadScripts.length; i++) {
+      const { code, port } = preloadScripts[i];
+      const { compileFunction } = require('vm');
+      const preloadInit = compileFunction(
+        code,
+        ['getBuiltin', 'port'],
+        {
+          filename: '<preload>',
+        },
+      );
+      const { BuiltinModule } = require('internal/bootstrap/realm');
+      // Calls the compiled preload source text gotten from the hook
+      // Since the parameters are named we use positional parameters
+      // see compileFunction above to cross reference the names
+      FunctionPrototypeCall(
+        preloadInit,
+        globalThis,
+        // Param getBuiltin
+        (builtinName) => {
+          if (BuiltinModule.canBeRequiredByUsers(builtinName) &&
+              BuiltinModule.canBeRequiredWithoutScheme(builtinName)) {
+            return require(builtinName);
+          }
+          throw new ERR_INVALID_ARG_VALUE('builtinName', builtinName);
+        },
+        // Param port
+        port,
+      );
+    }
+  }
+}
+ObjectSetPrototypeOf(HooksProxy.prototype, null);
 
 /**
  * A utility function to pluck the hooks from a user-defined loader.
@@ -665,3 +793,4 @@ function nextHookFactory(chain, meta, { validateArgs, validateOutput }) {
 
 
 exports.Hooks = Hooks;
+exports.HooksProxy = HooksProxy;
diff --git a/lib/internal/modules/esm/initialize_import_meta.js b/lib/internal/modules/esm/initialize_import_meta.js
index fe5ba4a3cc1248..c548f71bef837a 100644
--- a/lib/internal/modules/esm/initialize_import_meta.js
+++ b/lib/internal/modules/esm/initialize_import_meta.js
@@ -1,39 +1,50 @@
 'use strict';
 
 const { getOptionValue } = require('internal/options');
-const experimentalImportMetaResolve =
-  getOptionValue('--experimental-import-meta-resolve');
-const {
-  PromisePrototypeThen,
-  PromiseReject,
-} = primordials;
-const asyncESM = require('internal/process/esm_loader');
-
-function createImportMetaResolve(defaultParentUrl) {
-  return async function resolve(specifier, parentUrl = defaultParentUrl) {
-    return PromisePrototypeThen(
-      asyncESM.esmLoader.resolve(specifier, parentUrl),
-      ({ url }) => url,
-      (error) => (
-        error.code === 'ERR_UNSUPPORTED_DIR_IMPORT' ?
-          error.url : PromiseReject(error)),
-    );
+const experimentalImportMetaResolve = getOptionValue('--experimental-import-meta-resolve');
+
+/**
+ * Generate a function to be used as import.meta.resolve for a particular module.
+ * @param {string} defaultParentUrl The default base to use for resolution
+ * @param {typeof import('./loader.js').ModuleLoader} loader Reference to the current module loader
+ * @returns {(specifier: string, parentUrl?: string) => string} Function to assign to import.meta.resolve
+ */
+function createImportMetaResolve(defaultParentUrl, loader) {
+  return function resolve(specifier, parentUrl = defaultParentUrl) {
+    let url;
+
+    try {
+      ({ url } = loader.resolve(specifier, parentUrl));
+    } catch (error) {
+      if (error?.code === 'ERR_UNSUPPORTED_DIR_IMPORT') {
+        ({ url } = error);
+      } else {
+        throw error;
+      }
+    }
+
+    return url;
   };
 }
 
 /**
+ * Create the `import.meta` object for a module.
  * @param {object} meta
  * @param {{url: string}} context
+ * @param {typeof import('./loader.js').ModuleLoader} loader Reference to the current module loader
+ * @returns {{url: string, resolve?: Function}}
  */
-function initializeImportMeta(meta, context) {
+function initializeImportMeta(meta, context, loader) {
   const { url } = context;
 
   // Alphabetical
-  if (experimentalImportMetaResolve) {
-    meta.resolve = createImportMetaResolve(url);
+  if (experimentalImportMetaResolve && loader.loaderType !== 'internal') {
+    meta.resolve = createImportMetaResolve(url, loader);
   }
 
   meta.url = url;
+
+  return meta;
 }
 
 module.exports = {
diff --git a/lib/internal/modules/esm/loader.js b/lib/internal/modules/esm/loader.js
index 1fc25512b2c69c..a42319dba892c8 100644
--- a/lib/internal/modules/esm/loader.js
+++ b/lib/internal/modules/esm/loader.js
@@ -8,6 +8,7 @@ const {
   ArrayIsArray,
   FunctionPrototypeCall,
   ObjectSetPrototypeOf,
+  PromisePrototypeThen,
   SafePromiseAllReturnArrayLike,
   SafeWeakMap,
 } = primordials;
@@ -18,10 +19,10 @@ const {
 const { getOptionValue } = require('internal/options');
 const { pathToFileURL } = require('internal/url');
 const { emitExperimentalWarning } = require('internal/util');
-
 const {
   getDefaultConditions,
 } = require('internal/modules/esm/utils');
+let defaultResolve, defaultLoad, importMetaInitializer;
 
 function newModuleMap() {
   const ModuleMap = require('internal/modules/esm/module_map');
@@ -33,6 +34,14 @@ function getTranslators() {
   return translators;
 }
 
+/**
+ * @type {HooksProxy}
+ * Multiple loader instances exist for various, specific reasons (see code comments at site).
+ * In order to maintain consistency, we use a single worker (sandbox), which must sit apart of an
+ * individual loader instance.
+ */
+let hooksProxy;
+
 /**
  * @typedef {object} ExportedHooks
  * @property {Function} globalPreload Global preload hook.
@@ -60,17 +69,10 @@ function getTranslators() {
 
 
 /**
- * An ESMLoader instance is used as the main entry point for loading ES modules.
- * Currently, this is a singleton -- there is only one used for loading
- * the main module and everything in its dependency graph.
+ * This class covers the default case of an module loader instance where no custom user loaders are used.
+ * The below CustomizedModuleLoader class extends this one to support custom user loader hooks.
  */
-
-class ESMLoader {
-  #hooks;
-  #defaultResolve;
-  #defaultLoad;
-  #importMetaInitializer;
-
+class DefaultModuleLoader {
   /**
    * The conditions for resolving packages if `--conditions` is not used.
    */
@@ -96,24 +98,18 @@ class ESMLoader {
    */
   translators = getTranslators();
 
+  /**
+   * Type of loader.
+   * @type {'default' | 'internal'}
+   */
+  loaderType = 'default';
+
   constructor() {
-    if (getOptionValue('--experimental-loader').length > 0) {
-      emitExperimentalWarning('Custom ESM Loaders');
-    }
     if (getOptionValue('--experimental-network-imports')) {
       emitExperimentalWarning('Network Imports');
     }
   }
 
-  addCustomLoaders(userLoaders) {
-    const { Hooks } = require('internal/modules/esm/hooks');
-    this.#hooks = new Hooks(userLoaders);
-  }
-
-  preload() {
-    this.#hooks?.preload();
-  }
-
   async eval(
     source,
     url = pathToFileURL(`${process.cwd()}/[eval${++this.evalIndex}]`).href,
@@ -153,23 +149,14 @@ class ESMLoader {
    *                                     point.
    * @param {Record<string, string>} importAssertions Validations for the
    *                                                  module import.
-   * @returns {Promise<ModuleJob>} The (possibly pending) module job
+   * @returns {ModuleJob} The (possibly pending) module job
    */
-  async getModuleJob(specifier, parentURL, importAssertions) {
-    let importAssertionsForResolve;
-
-    // We can skip cloning if there are no user-provided loaders because
-    // the Node.js default resolve hook does not use import assertions.
-    if (this.#hooks?.hasCustomResolveOrLoadHooks) {
-      // This method of cloning only works so long as import assertions cannot contain objects as values,
-      // which they currently cannot per spec.
-      importAssertionsForResolve = {
-        __proto__: null,
-        ...importAssertions,
-      };
-    }
+  getModuleJob(specifier, parentURL, importAssertions) {
+    const resolveResult = this.resolve(specifier, parentURL, importAssertions);
+    return this.getJobFromResolveResult(resolveResult, parentURL, importAssertions);
+  }
 
-    const resolveResult = await this.resolve(specifier, parentURL, importAssertionsForResolve);
+  getJobFromResolveResult(resolveResult, parentURL, importAssertions) {
     const { url, format } = resolveResult;
     const resolvedImportAssertions = resolveResult.importAssertions ?? importAssertions;
 
@@ -273,9 +260,12 @@ class ESMLoader {
     const jobs = new Array(count);
 
     for (let i = 0; i < count; i++) {
-      jobs[i] = this.getModuleJob(specifiers[i], parentURL, importAssertions)
-        .then((job) => job.run())
-        .then(({ module }) => module.getNamespace());
+      jobs[i] = PromisePrototypeThen(
+        this
+          .getModuleJob(specifiers[i], parentURL, importAssertions)
+          .run(),
+        ({ module }) => module.getNamespace(),
+      );
     }
 
     const namespaces = await SafePromiseAllReturnArrayLike(jobs);
@@ -300,24 +290,20 @@ class ESMLoader {
    *                                   be resolved.
    * @param {string} [parentURL] The URL path of the module's parent.
    * @param {ImportAssertions} importAssertions Assertions from the import
-   *                                              statement or expression.
-   * @returns {Promise<{ format: string, url: URL['href'] }>}
+   *                                            statement or expression.
+   * @returns {{ format: string, url: URL['href'] }}
    */
-  async resolve(originalSpecifier, parentURL, importAssertions) {
-    if (this.#hooks) {
-      return this.#hooks.resolve(originalSpecifier, parentURL, importAssertions);
-    }
-    if (!this.#defaultResolve) {
-      this.#defaultResolve = require('internal/modules/esm/resolve').defaultResolve;
-    }
+  resolve(originalSpecifier, parentURL, importAssertions) {
+    defaultResolve ??= require('internal/modules/esm/resolve').defaultResolve;
+
     const context = {
       __proto__: null,
       conditions: this.#defaultConditions,
       importAssertions,
       parentURL,
     };
-    return this.#defaultResolve(originalSpecifier, context);
 
+    return defaultResolve(originalSpecifier, context);
   }
 
   /**
@@ -328,36 +314,118 @@ class ESMLoader {
    * @returns {Promise<{ format: ModuleFormat, source: ModuleSource }>}
    */
   async load(url, context) {
-    let loadResult;
-    if (this.#hooks) {
-      loadResult = await this.#hooks.load(url, context);
-    } else {
-      if (!this.#defaultLoad) {
-        this.#defaultLoad = require('internal/modules/esm/load').defaultLoad;
-      }
-      loadResult = await this.#defaultLoad(url, context);
-    }
+    defaultLoad ??= require('internal/modules/esm/load').defaultLoad;
+
+    const result = await defaultLoad(url, context);
+    this.validateLoadResult(url, result?.format);
+    return result;
+  }
 
-    const { format } = loadResult;
+  validateLoadResult(url, format) {
     if (format == null) {
       require('internal/modules/esm/load').throwUnknownModuleFormat(url, format);
     }
-
-    return loadResult;
   }
 
   importMetaInitialize(meta, context) {
-    if (this.#hooks) {
-      this.#hooks.importMetaInitialize(meta, context);
-    } else {
-      if (!this.#importMetaInitializer) {
-        this.#importMetaInitializer = require('internal/modules/esm/initialize_import_meta').initializeImportMeta;
-      }
-      this.#importMetaInitializer(meta, context);
+    importMetaInitializer ??= require('internal/modules/esm/initialize_import_meta').initializeImportMeta;
+    meta = importMetaInitializer(meta, context, this);
+    return meta;
+  }
+}
+ObjectSetPrototypeOf(DefaultModuleLoader.prototype, null);
+
+
+class CustomizedModuleLoader extends DefaultModuleLoader {
+  /**
+   * Instantiate a module loader that uses user-provided custom loader hooks.
+   */
+  constructor() {
+    super();
+
+    if (hooksProxy) {
+      // The worker proxy is shared across all instances, so don't recreate it if it already exists.
+      return;
     }
+    const { HooksProxy } = require('internal/modules/esm/hooks');
+    hooksProxy = new HooksProxy(); // The user's custom hooks are loaded within the worker as part of its startup.
+  }
+
+  /**
+   * Resolve the location of the module.
+   *
+   * @param {string} originalSpecifier The specified URL path of the module to
+   *                                   be resolved.
+   * @param {string} [parentURL] The URL path of the module's parent.
+   * @param {ImportAssertions} importAssertions Assertions from the import
+   *                                            statement or expression.
+   * @returns {{ format: string, url: URL['href'] }}
+   */
+  resolve(originalSpecifier, parentURL, importAssertions) {
+    return hooksProxy.makeSyncRequest('resolve', originalSpecifier, parentURL, importAssertions);
+  }
+
+  async #getModuleJob(specifier, parentURL, importAssertions) {
+    const resolveResult = await hooksProxy.makeAsyncRequest('resolve', specifier, parentURL, importAssertions);
+
+    return this.getJobFromResolveResult(resolveResult, parentURL, importAssertions);
+  }
+  getModuleJob(specifier, parentURL, importAssertions) {
+    const jobPromise = this.#getModuleJob(specifier, parentURL, importAssertions);
+
+    return {
+      run() {
+        return PromisePrototypeThen(jobPromise, (job) => job.run());
+      },
+      get modulePromise() {
+        return PromisePrototypeThen(jobPromise, (job) => job.modulePromise);
+      },
+      get linked() {
+        return PromisePrototypeThen(jobPromise, (job) => job.linked);
+      },
+    };
+  }
+
+  /**
+   * Provide source that is understood by one of Node's translators.
+   *
+   * @param {URL['href']} url The URL/path of the module to be loaded
+   * @param {object} [context] Metadata about the module
+   * @returns {Promise<{ format: ModuleFormat, source: ModuleSource }>}
+   */
+  async load(url, context) {
+    const result = await hooksProxy.makeAsyncRequest('load', url, context);
+    this.validateLoadResult(url, result?.format);
+
+    return result;
   }
 }
 
-ObjectSetPrototypeOf(ESMLoader.prototype, null);
 
-exports.ESMLoader = ESMLoader;
+let emittedExperimentalWarning = false;
+/**
+ * A loader instance is used as the main entry point for loading ES modules. Currently, this is a singleton; there is
+ * only one used for loading the main module and everything in its dependency graph, though separate instances of this
+ * class might be instantiated as part of bootstrap for other purposes.
+ * @param {boolean} useCustomLoadersIfPresent If the user has provided loaders via the --loader flag, use them.
+ * @returns {DefaultModuleLoader | CustomizedModuleLoader}
+ */
+function createModuleLoader(useCustomLoadersIfPresent = true) {
+  if (useCustomLoadersIfPresent) {
+    const userLoaderPaths = getOptionValue('--experimental-loader');
+    if (userLoaderPaths.length > 0) {
+      if (!emittedExperimentalWarning) {
+        emitExperimentalWarning('Custom ESM Loaders');
+        emittedExperimentalWarning = true;
+      }
+      return new CustomizedModuleLoader();
+    }
+  }
+
+  return new DefaultModuleLoader();
+}
+
+module.exports = {
+  DefaultModuleLoader,
+  createModuleLoader,
+};
diff --git a/lib/internal/modules/esm/module_job.js b/lib/internal/modules/esm/module_job.js
index 2a0208dfc5cf8f..2cf2813a6dcf7f 100644
--- a/lib/internal/modules/esm/module_job.js
+++ b/lib/internal/modules/esm/module_job.js
@@ -72,10 +72,9 @@ class ModuleJob {
       // so that circular dependencies can't cause a deadlock by two of
       // these `link` callbacks depending on each other.
       const dependencyJobs = [];
-      const promises = this.module.link(async (specifier, assertions) => {
-        const jobPromise = this.loader.getModuleJob(specifier, url, assertions);
-        ArrayPrototypePush(dependencyJobs, jobPromise);
-        const job = await jobPromise;
+      const promises = this.module.link((specifier, assertions) => {
+        const job = this.loader.getModuleJob(specifier, url, assertions);
+        ArrayPrototypePush(dependencyJobs, job);
         return job.modulePromise;
       });
 
diff --git a/lib/internal/modules/esm/resolve.js b/lib/internal/modules/esm/resolve.js
index 5212e2ce17758d..0dc7a9ae1d6690 100644
--- a/lib/internal/modules/esm/resolve.js
+++ b/lib/internal/modules/esm/resolve.js
@@ -41,9 +41,10 @@ const preserveSymlinksMain = getOptionValue('--preserve-symlinks-main');
 const experimentalNetworkImports =
   getOptionValue('--experimental-network-imports');
 const typeFlag = getOptionValue('--input-type');
-const { URL, pathToFileURL, fileURLToPath } = require('internal/url');
+const { URL, pathToFileURL, fileURLToPath, isURL } = require('internal/url');
 const {
   ERR_INPUT_TYPE_NOT_ALLOWED,
+  ERR_INVALID_ARG_TYPE,
   ERR_INVALID_MODULE_SPECIFIER,
   ERR_INVALID_PACKAGE_CONFIG,
   ERR_INVALID_PACKAGE_TARGET,
@@ -935,6 +936,18 @@ function checkIfDisallowedImport(specifier, parsed, parsedParentURL) {
   }
 }
 
+/**
+ * Validate user-input in `context` supplied by a custom loader.
+ */
+function throwIfInvalidParentURL(parentURL) {
+  if (parentURL === undefined) {
+    return; // Main entry point, so no parent
+  }
+  if (typeof parentURL !== 'string' && !isURL(parentURL)) {
+    throw new ERR_INVALID_ARG_TYPE('parentURL', ['string', 'URL'], parentURL);
+  }
+}
+
 function throwIfUnsupportedURLProtocol(url) {
   if (url.protocol !== 'file:' && url.protocol !== 'data:' &&
       url.protocol !== 'node:') {
@@ -963,8 +976,9 @@ function throwIfUnsupportedURLScheme(parsed, experimentalNetworkImports) {
   }
 }
 
-async function defaultResolve(specifier, context = {}) {
+function defaultResolve(specifier, context = {}) {
   let { parentURL, conditions } = context;
+  throwIfInvalidParentURL(parentURL);
   if (parentURL && policy?.manifest) {
     const redirects = policy.manifest.getDependencyMapper(parentURL);
     if (redirects) {
@@ -1100,6 +1114,7 @@ module.exports = {
   getPackageType,
   packageExportsResolve,
   packageImportsResolve,
+  throwIfInvalidParentURL,
 };
 
 // cycle
@@ -1109,11 +1124,11 @@ const {
 
 if (policy) {
   const $defaultResolve = defaultResolve;
-  module.exports.defaultResolve = async function defaultResolve(
+  module.exports.defaultResolve = function defaultResolve(
     specifier,
     context,
   ) {
-    const ret = await $defaultResolve(specifier, context);
+    const ret = $defaultResolve(specifier, context);
     // This is a preflight check to avoid data exfiltration by query params etc.
     policy.manifest.mightAllow(ret.url, () =>
       new ERR_MANIFEST_DEPENDENCY_MISSING(
diff --git a/lib/internal/modules/esm/shared_constants.js b/lib/internal/modules/esm/shared_constants.js
new file mode 100644
index 00000000000000..4200bc87367d14
--- /dev/null
+++ b/lib/internal/modules/esm/shared_constants.js
@@ -0,0 +1,25 @@
+// This file contains the definition for the constant values that must be
+// available to both the main thread and the loader thread.
+
+'use strict';
+
+/*
+The shared memory area is divided in 1 32-bit long section. It has to be 32-bit long as
+`Atomics.notify` only works with `Int32Array` objects.
+
+--32-bits--
+    ^
+    |
+    |
+WORKER_TO_MAIN_THREAD_NOTIFICATION
+
+WORKER_TO_MAIN_THREAD_NOTIFICATION is only used to send notifications, its value is going to
+increase every time the worker sends a notification to the main thread.
+
+*/
+
+module.exports = {
+  WORKER_TO_MAIN_THREAD_NOTIFICATION: 0,
+
+  SHARED_MEMORY_BYTE_LENGTH: 1 * 4,
+};
diff --git a/lib/internal/modules/esm/utils.js b/lib/internal/modules/esm/utils.js
index bf3edc86518b4c..1c01dd13b3ab21 100644
--- a/lib/internal/modules/esm/utils.js
+++ b/lib/internal/modules/esm/utils.js
@@ -1,6 +1,8 @@
 'use strict';
+
 const {
   ArrayIsArray,
+  PromisePrototypeThen,
   SafeSet,
   SafeWeakMap,
   ObjectFreeze,
@@ -10,9 +12,9 @@ const {
   ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING,
   ERR_INVALID_ARG_VALUE,
 } = require('internal/errors').codes;
-
 const { getOptionValue } = require('internal/options');
-
+const { pathToFileURL } = require('internal/url');
+const { kEmptyObject } = require('internal/util');
 const {
   setImportModuleDynamicallyCallback,
   setInitializeImportMetaObjectCallback,
@@ -73,7 +75,7 @@ function initializeImportMetaObject(wrap, meta) {
   if (callbackMap.has(wrap)) {
     const { initializeImportMeta } = callbackMap.get(wrap);
     if (initializeImportMeta !== undefined) {
-      initializeImportMeta(meta, getModuleFromWrap(wrap) || wrap);
+      meta = initializeImportMeta(meta, getModuleFromWrap(wrap) || wrap);
     }
   }
 }
@@ -97,9 +99,70 @@ function initializeESM() {
   setImportModuleDynamicallyCallback(importModuleDynamicallyCallback);
 }
 
+async function initializeHooks() {
+  const customLoaderPaths = getOptionValue('--experimental-loader');
+
+  let cwd;
+  try {
+    // `process.cwd()` can fail if the parent directory is deleted while the process runs.
+    cwd = process.cwd() + '/';
+  } catch {
+    cwd = '/';
+  }
+
+
+  const { Hooks } = require('internal/modules/esm/hooks');
+  const hooks = new Hooks();
+
+  const { DefaultModuleLoader } = require('internal/modules/esm/loader');
+  class ModuleLoader extends DefaultModuleLoader {
+    loaderType = 'internal';
+    async #getModuleJob(specifier, parentURL, importAssertions) {
+      const resolveResult = await hooks.resolve(specifier, parentURL, importAssertions);
+      return this.getJobFromResolveResult(resolveResult, parentURL, importAssertions);
+    }
+    getModuleJob(specifier, parentURL, importAssertions) {
+      const jobPromise = this.#getModuleJob(specifier, parentURL, importAssertions);
+      return {
+        run() {
+          return PromisePrototypeThen(jobPromise, (job) => job.run());
+        },
+        get modulePromise() {
+          return PromisePrototypeThen(jobPromise, (job) => job.modulePromise);
+        },
+        get linked() {
+          return PromisePrototypeThen(jobPromise, (job) => job.linked);
+        },
+      };
+    }
+    load(url, context) { return hooks.load(url, context); }
+  }
+  const privateModuleLoader = new ModuleLoader();
+
+  const parentURL = pathToFileURL(cwd).href;
+
+  for (let i = 0; i < customLoaderPaths.length; i++) {
+    const customLoaderPath = customLoaderPaths[i];
+
+    // Importation must be handled by internal loader to avoid polluting user-land
+    const keyedExportsSublist = await privateModuleLoader.import(
+      [customLoaderPath], // Import can handle multiple paths, but custom loaders must be sequential
+      parentURL,
+      kEmptyObject,
+    );
+
+    hooks.addCustomLoaders(keyedExportsSublist);
+  }
+
+  const preloadScripts = hooks.initializeGlobalPreload();
+
+  return { __proto__: null, hooks, preloadScripts };
+}
+
 module.exports = {
   setCallbackForWrap,
   initializeESM,
+  initializeHooks,
   getDefaultConditions,
   getConditionsSet,
 };
diff --git a/lib/internal/modules/esm/worker.js b/lib/internal/modules/esm/worker.js
new file mode 100644
index 00000000000000..8a1ef9add7060f
--- /dev/null
+++ b/lib/internal/modules/esm/worker.js
@@ -0,0 +1,210 @@
+'use strict';
+
+const {
+  DataViewPrototypeGetBuffer,
+  Int32Array,
+  PromisePrototypeThen,
+  ReflectApply,
+  SafeSet,
+  TypedArrayPrototypeGetBuffer,
+  globalThis: {
+    Atomics: {
+      add: AtomicsAdd,
+      notify: AtomicsNotify,
+    },
+  },
+} = primordials;
+const assert = require('internal/assert');
+const { clearImmediate, setImmediate } = require('timers');
+const {
+  hasUncaughtExceptionCaptureCallback,
+} = require('internal/process/execution');
+const {
+  isArrayBuffer,
+  isDataView,
+  isTypedArray,
+} = require('util/types');
+
+const { receiveMessageOnPort } = require('internal/worker/io');
+const {
+  WORKER_TO_MAIN_THREAD_NOTIFICATION,
+} = require('internal/modules/esm/shared_constants');
+const { initializeESM, initializeHooks } = require('internal/modules/esm/utils');
+
+
+function transferArrayBuffer(hasError, source) {
+  if (hasError || source == null) return;
+  if (isArrayBuffer(source)) return [source];
+  if (isTypedArray(source)) return [TypedArrayPrototypeGetBuffer(source)];
+  if (isDataView(source)) return [DataViewPrototypeGetBuffer(source)];
+}
+
+function wrapMessage(status, body) {
+  if (status === 'success' || body === null || typeof body !== 'object') {
+    return { status, body };
+  }
+
+  let serialized;
+  let serializationFailed;
+  try {
+    const { serializeError } = require('internal/error_serdes');
+    serialized = serializeError(body);
+  } catch {
+    serializationFailed = true;
+  }
+
+  return {
+    status,
+    body: {
+      serialized,
+      serializationFailed,
+    },
+  };
+}
+
+async function customizedModuleWorker(lock, syncCommPort, errorHandler) {
+  let hooks, preloadScripts, initializationError;
+  let hasInitializationError = false;
+
+  try {
+    initializeESM();
+    const initResult = await initializeHooks();
+    hooks = initResult.hooks;
+    preloadScripts = initResult.preloadScripts;
+  } catch (exception) {
+    // If there was an error while parsing and executing a user loader, for example if because a
+    // loader contained a syntax error, then we need to send the error to the main thread so it can
+    // be thrown and printed.
+    hasInitializationError = true;
+    initializationError = exception;
+  }
+
+  syncCommPort.on('message', handleMessage);
+
+  if (hasInitializationError) {
+    syncCommPort.postMessage(wrapMessage('error', initializationError));
+  } else {
+    syncCommPort.postMessage(wrapMessage('success', { preloadScripts }), preloadScripts.map(({ port }) => port));
+  }
+
+  // We're ready, so unlock the main thread.
+  AtomicsAdd(lock, WORKER_TO_MAIN_THREAD_NOTIFICATION, 1);
+  AtomicsNotify(lock, WORKER_TO_MAIN_THREAD_NOTIFICATION);
+
+  let immediate;
+  function checkForMessages() {
+    immediate = setImmediate(checkForMessages).unref();
+    // We need to let the event loop tick a few times to give the main thread a chance to send
+    // follow-up messages.
+    const response = receiveMessageOnPort(syncCommPort);
+
+    if (response !== undefined) {
+      PromisePrototypeThen(handleMessage(response.message), undefined, errorHandler);
+    }
+  }
+
+  const unsettledResponsePorts = new SafeSet();
+
+  process.on('beforeExit', () => {
+    for (const port of unsettledResponsePorts) {
+      port.postMessage(wrapMessage('never-settle'));
+    }
+    unsettledResponsePorts.clear();
+
+    AtomicsAdd(lock, WORKER_TO_MAIN_THREAD_NOTIFICATION, 1);
+    AtomicsNotify(lock, WORKER_TO_MAIN_THREAD_NOTIFICATION);
+
+    // Attach back the event handler.
+    syncCommPort.on('message', handleMessage);
+    // Also check synchronously for a message, in case it's already there.
+    clearImmediate(immediate);
+    checkForMessages();
+    // We don't need the sync check after this tick, as we already have added the event handler.
+    clearImmediate(immediate);
+    // Add some work for next tick so the worker cannot exit.
+    setImmediate(() => {});
+  });
+
+  async function handleMessage({ method, args, port }) {
+    // Each potential exception needs to be caught individually so that the correct error is sent to
+    // the main thread.
+    let hasError = false;
+    let shouldRemoveGlobalErrorHandler = false;
+    assert(typeof hooks[method] === 'function');
+    if (port == null && !hasUncaughtExceptionCaptureCallback()) {
+      // When receiving sync messages, we want to unlock the main thread when there's an exception.
+      process.on('uncaughtException', errorHandler);
+      shouldRemoveGlobalErrorHandler = true;
+    }
+
+    // We are about to yield the execution with `await ReflectApply` below. In case the code
+    // following the `await` never runs, we remove the message handler so the `beforeExit` event
+    // can be triggered.
+    syncCommPort.off('message', handleMessage);
+
+    // We keep checking for new messages to not miss any.
+    clearImmediate(immediate);
+    immediate = setImmediate(checkForMessages).unref();
+
+    unsettledResponsePorts.add(port ?? syncCommPort);
+
+    let response;
+    try {
+      response = await ReflectApply(hooks[method], hooks, args);
+    } catch (exception) {
+      hasError = true;
+      response = exception;
+    }
+
+    unsettledResponsePorts.delete(port ?? syncCommPort);
+
+    // Send the method response (or exception) to the main thread.
+    try {
+      (port ?? syncCommPort).postMessage(
+        wrapMessage(hasError ? 'error' : 'success', response),
+        transferArrayBuffer(hasError, response?.source),
+      );
+    } catch (exception) {
+      // Or send the exception thrown when trying to send the response.
+      (port ?? syncCommPort).postMessage(wrapMessage('error', exception));
+    }
+
+    AtomicsAdd(lock, WORKER_TO_MAIN_THREAD_NOTIFICATION, 1);
+    AtomicsNotify(lock, WORKER_TO_MAIN_THREAD_NOTIFICATION);
+    if (shouldRemoveGlobalErrorHandler) {
+      process.off('uncaughtException', errorHandler);
+    }
+
+    syncCommPort.off('message', handleMessage);
+    // We keep checking for new messages to not miss any.
+    clearImmediate(immediate);
+    immediate = setImmediate(checkForMessages).unref();
+  }
+}
+
+/**
+ * ! Run everything possible within this function so errors get reported.
+ */
+module.exports = function setupModuleWorker(workerData, syncCommPort) {
+  const lock = new Int32Array(workerData.lock);
+
+  function errorHandler(err, origin = 'unhandledRejection') {
+    AtomicsAdd(lock, WORKER_TO_MAIN_THREAD_NOTIFICATION, 1);
+    AtomicsNotify(lock, WORKER_TO_MAIN_THREAD_NOTIFICATION);
+    process.off('uncaughtException', errorHandler);
+    if (hasUncaughtExceptionCaptureCallback()) {
+      process._fatalException(err);
+      return;
+    }
+    internalBinding('errors').triggerUncaughtException(
+      err,
+      origin === 'unhandledRejection',
+    );
+  }
+
+  return PromisePrototypeThen(
+    customizedModuleWorker(lock, syncCommPort, errorHandler),
+    undefined,
+    errorHandler,
+  );
+};
diff --git a/lib/internal/process/esm_loader.js b/lib/internal/process/esm_loader.js
index 9a04e094e001c4..e7d70ebbca1ca4 100644
--- a/lib/internal/process/esm_loader.js
+++ b/lib/internal/process/esm_loader.js
@@ -1,105 +1,48 @@
 'use strict';
 
-const {
-  ArrayIsArray,
-  ArrayPrototypePushApply,
-} = primordials;
-
-const { ESMLoader } = require('internal/modules/esm/loader');
+const { createModuleLoader } = require('internal/modules/esm/loader');
+const { getOptionValue } = require('internal/options');
 const {
   hasUncaughtExceptionCaptureCallback,
 } = require('internal/process/execution');
 const { pathToFileURL } = require('internal/url');
 const { kEmptyObject } = require('internal/util');
 
-const esmLoader = new ESMLoader();
-exports.esmLoader = esmLoader;
-
-// Module.runMain() causes loadESM() to re-run (which it should do); however, this should NOT cause
-// ESM to be re-initialized; doing so causes duplicate custom loaders to be added to the public
-// esmLoader.
-let isESMInitialized = false;
-
-/**
- * Causes side-effects: user-defined loader hooks are added to esmLoader.
- * @returns {void}
- */
-async function initializeLoader() {
-  if (isESMInitialized) { return; }
-
-  const { getOptionValue } = require('internal/options');
-  const customLoaders = getOptionValue('--experimental-loader');
-  const preloadModules = getOptionValue('--import');
-
-  let cwd;
-  try {
-    cwd = process.cwd() + '/';
-  } catch {
-    cwd = '/';
-  }
-
-  const internalEsmLoader = new ESMLoader();
-  const allLoaders = [];
-
-  const parentURL = pathToFileURL(cwd).href;
-
-  for (let i = 0; i < customLoaders.length; i++) {
-    const customLoader = customLoaders[i];
-
-    // Importation must be handled by internal loader to avoid polluting user-land
-    const keyedExportsSublist = await internalEsmLoader.import(
-      [customLoader],
-      parentURL,
-      kEmptyObject,
-    );
-
-    internalEsmLoader.addCustomLoaders(keyedExportsSublist);
-    ArrayPrototypePushApply(allLoaders, keyedExportsSublist);
-  }
-
-  // Hooks must then be added to external/public loader
-  // (so they're triggered in userland)
-  esmLoader.addCustomLoaders(allLoaders);
-  esmLoader.preload();
-
-  // Preload after loaders are added so they can be used
-  if (preloadModules?.length) {
-    await loadModulesInIsolation(parentURL, preloadModules, allLoaders);
-  }
-
-  isESMInitialized = true;
-}
-
-function loadModulesInIsolation(parentURL, specifiers, loaders = []) {
-  if (!ArrayIsArray(specifiers) || specifiers.length === 0) { return; }
-
-  // A separate loader instance is necessary to avoid cross-contamination
-  // between internal Node.js and userland. For example, a module with internal
-  // state (such as a counter) should be independent.
-  const internalEsmLoader = new ESMLoader();
-  internalEsmLoader.addCustomLoaders(loaders);
-  internalEsmLoader.preload();
-
-  // Importation must be handled by internal loader to avoid polluting userland
-  return internalEsmLoader.import(
-    specifiers,
-    parentURL,
-    kEmptyObject,
-  );
-}
-
-exports.loadESM = async function loadESM(callback) {
-  try {
-    await initializeLoader();
-    await callback(esmLoader);
-  } catch (err) {
-    if (hasUncaughtExceptionCaptureCallback()) {
-      process._fatalException(err);
-      return;
+let esmLoader;
+
+module.exports = {
+  get esmLoader() {
+    return esmLoader ??= createModuleLoader(true);
+  },
+  async loadESM(callback) {
+    esmLoader ??= createModuleLoader(true);
+    try {
+      const userImports = getOptionValue('--import');
+      if (userImports.length > 0) {
+        let cwd;
+        try {
+          // `process.cwd()` can fail if the parent directory is deleted while the process runs.
+          cwd = process.cwd() + '/';
+        } catch {
+          cwd = '/';
+        }
+        const parentURL = pathToFileURL(cwd).href;
+        await esmLoader.import(
+          userImports,
+          parentURL,
+          kEmptyObject,
+        );
+      }
+      await callback(esmLoader);
+    } catch (err) {
+      if (hasUncaughtExceptionCaptureCallback()) {
+        process._fatalException(err);
+        return;
+      }
+      internalBinding('errors').triggerUncaughtException(
+        err,
+        true, /* fromPromise */
+      );
     }
-    internalBinding('errors').triggerUncaughtException(
-      err,
-      true, /* fromPromise */
-    );
-  }
+  },
 };
diff --git a/lib/internal/worker.js b/lib/internal/worker.js
index 3b4b2f6ffaf0dc..eda9dbcdeb5c04 100644
--- a/lib/internal/worker.js
+++ b/lib/internal/worker.js
@@ -45,6 +45,7 @@ const { getOptionValue } = require('internal/options');
 const workerIo = require('internal/worker/io');
 const {
   drainMessagePort,
+  receiveMessageOnPort,
   MessageChannel,
   messageTypes,
   kPort,
@@ -82,6 +83,7 @@ const kOnCouldNotSerializeErr = Symbol('kOnCouldNotSerializeErr');
 const kOnErrorMessage = Symbol('kOnErrorMessage');
 const kParentSideStdio = Symbol('kParentSideStdio');
 const kLoopStartTime = Symbol('kLoopStartTime');
+const kIsInternal = Symbol('kIsInternal');
 const kIsOnline = Symbol('kIsOnline');
 
 const SHARE_ENV = SymbolFor('nodejs.worker_threads.SHARE_ENV');
@@ -128,7 +130,13 @@ function assignEnvironmentData(data) {
 class Worker extends EventEmitter {
   constructor(filename, options = kEmptyObject) {
     super();
-    debug(`[${threadId}] create new worker`, filename, options);
+    const isInternal = arguments[2] === kIsInternal;
+    debug(
+      `[${threadId}] create new worker`,
+      filename,
+      options,
+      `isInternal: ${isInternal}`,
+    );
     if (options.execArgv)
       validateArray(options.execArgv, 'options.execArgv');
 
@@ -139,7 +147,10 @@ class Worker extends EventEmitter {
     }
 
     let url, doEval;
-    if (options.eval) {
+    if (isInternal) {
+      doEval = 'internal';
+      url = `node:${filename}`;
+    } else if (options.eval) {
       if (typeof filename !== 'string') {
         throw new ERR_INVALID_ARG_VALUE(
           'options.eval',
@@ -195,12 +206,14 @@ class Worker extends EventEmitter {
       name = StringPrototypeTrim(options.name);
     }
 
+    debug('instantiating Worker.', `url: ${url}`, `doEval: ${doEval}`);
     // Set up the C++ handle for the worker, as well as some internal wiring.
     this[kHandle] = new WorkerImpl(url,
                                    env === process.env ? null : env,
                                    options.execArgv,
                                    parseResourceLimits(options.resourceLimits),
                                    !!(options.trackUnmanagedFds ?? true),
+                                   isInternal,
                                    name);
     if (this[kHandle].invalidExecArgv) {
       throw new ERR_WORKER_INVALID_EXEC_ARGV(this[kHandle].invalidExecArgv);
@@ -252,6 +265,7 @@ class Worker extends EventEmitter {
       type: messageTypes.LOAD_SCRIPT,
       filename,
       doEval,
+      isInternal,
       cwdCounter: cwdCounter || workerIo.sharedCwdCounter,
       workerData: options.workerData,
       environmentData,
@@ -441,6 +455,20 @@ class Worker extends EventEmitter {
   }
 }
 
+/**
+ * A worker which has an internal module for entry point (e.g. internal/module/esm/worker).
+ * Internal workers bypass the permission model.
+ */
+class InternalWorker extends Worker {
+  constructor(filename, options) {
+    super(filename, options, kIsInternal);
+  }
+
+  receiveMessageSync() {
+    return receiveMessageOnPort(this[kPublicPort]);
+  }
+}
+
 function pipeWithoutWarning(source, dest) {
   const sourceMaxListeners = source._maxListeners;
   const destMaxListeners = dest._maxListeners;
@@ -505,6 +533,7 @@ function eventLoopUtilization(util1, util2) {
 
 module.exports = {
   ownsProcessState,
+  kIsOnline,
   isMainThread,
   SHARE_ENV,
   resourceLimits:
@@ -513,5 +542,6 @@ module.exports = {
   getEnvironmentData,
   assignEnvironmentData,
   threadId,
+  InternalWorker,
   Worker,
 };
diff --git a/src/node_worker.cc b/src/node_worker.cc
index 5aa8a06b9cfbea..7be78dcdb93d1d 100644
--- a/src/node_worker.cc
+++ b/src/node_worker.cc
@@ -459,8 +459,12 @@ Worker::~Worker() {
 
 void Worker::New(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
-  THROW_IF_INSUFFICIENT_PERMISSIONS(
-      env, permission::PermissionScope::kWorkerThreads, "");
+  auto is_internal = args[5];
+  CHECK(is_internal->IsBoolean());
+  if (is_internal->IsFalse()) {
+    THROW_IF_INSUFFICIENT_PERMISSIONS(
+        env, permission::PermissionScope::kWorkerThreads, "");
+  }
   Isolate* isolate = args.GetIsolate();
 
   CHECK(args.IsConstructCall());
@@ -484,9 +488,9 @@ void Worker::New(const FunctionCallbackInfo<Value>& args) {
     url.append(value.out(), value.length());
   }
 
-  if (!args[5]->IsNullOrUndefined()) {
+  if (!args[6]->IsNullOrUndefined()) {
     Utf8Value value(
-        isolate, args[5]->ToString(env->context()).FromMaybe(Local<String>()));
+        isolate, args[6]->ToString(env->context()).FromMaybe(Local<String>()));
     name.append(value.out(), value.length());
   }
 
diff --git a/test/es-module/test-esm-import-meta-resolve.mjs b/test/es-module/test-esm-import-meta-resolve.mjs
index dc45610b460280..843ca6d747140a 100644
--- a/test/es-module/test-esm-import-meta-resolve.mjs
+++ b/test/es-module/test-esm-import-meta-resolve.mjs
@@ -1,36 +1,32 @@
 // Flags: --experimental-import-meta-resolve
-import { mustCall } from '../common/index.mjs';
+import '../common/index.mjs';
 import assert from 'assert';
 
 const dirname = import.meta.url.slice(0, import.meta.url.lastIndexOf('/') + 1);
 const fixtures = dirname.slice(0, dirname.lastIndexOf('/', dirname.length - 2) + 1) + 'fixtures/';
 
-(async () => {
-  assert.strictEqual(await import.meta.resolve('./test-esm-import-meta.mjs'),
-                     dirname + 'test-esm-import-meta.mjs');
-  try {
-    await import.meta.resolve('./notfound.mjs');
-    assert.fail();
-  } catch (e) {
-    assert.strictEqual(e.code, 'ERR_MODULE_NOT_FOUND');
-  }
-  assert.strictEqual(
-    await import.meta.resolve('../fixtures/empty-with-bom.txt'),
-    fixtures + 'empty-with-bom.txt');
-  assert.strictEqual(await import.meta.resolve('../fixtures/'), fixtures);
-  assert.strictEqual(
-    await import.meta.resolve('../fixtures/', import.meta.url),
-    fixtures);
-  assert.strictEqual(
-    await import.meta.resolve('../fixtures/', new URL(import.meta.url)),
-    fixtures);
-  await Promise.all(
-    [[], {}, Symbol(), 0, 1, 1n, 1.1, () => {}, true, false].map((arg) =>
-      assert.rejects(import.meta.resolve('../fixtures/', arg), {
-        code: 'ERR_INVALID_ARG_TYPE',
-      })
-    )
-  );
-  assert.strictEqual(await import.meta.resolve('baz/', fixtures),
-                     fixtures + 'node_modules/baz/');
-})().then(mustCall());
+assert.strictEqual(import.meta.resolve('./test-esm-import-meta.mjs'),
+                   dirname + 'test-esm-import-meta.mjs');
+try {
+  import.meta.resolve('./notfound.mjs');
+  assert.fail();
+} catch (e) {
+  assert.strictEqual(e.code, 'ERR_MODULE_NOT_FOUND');
+}
+assert.strictEqual(
+  import.meta.resolve('../fixtures/empty-with-bom.txt'),
+  fixtures + 'empty-with-bom.txt');
+assert.strictEqual(import.meta.resolve('../fixtures/'), fixtures);
+assert.strictEqual(
+  import.meta.resolve('../fixtures/', import.meta.url),
+  fixtures);
+assert.strictEqual(
+  import.meta.resolve('../fixtures/', new URL(import.meta.url)),
+  fixtures);
+[[], {}, Symbol(), 0, 1, 1n, 1.1, () => {}, true, false].map((arg) =>
+  assert.throws(() => import.meta.resolve('../fixtures/', arg), {
+    code: 'ERR_INVALID_ARG_TYPE',
+  })
+);
+assert.strictEqual(import.meta.resolve('baz/', fixtures),
+                   fixtures + 'node_modules/baz/');
diff --git a/test/es-module/test-esm-loader-modulemap.js b/test/es-module/test-esm-loader-modulemap.js
index 190676ec725cd2..093a4f6b3ef162 100644
--- a/test/es-module/test-esm-loader-modulemap.js
+++ b/test/es-module/test-esm-loader-modulemap.js
@@ -4,7 +4,7 @@
 require('../common');
 
 const { strictEqual, throws } = require('assert');
-const { ESMLoader } = require('internal/modules/esm/loader');
+const { createModuleLoader } = require('internal/modules/esm/loader');
 const ModuleMap = require('internal/modules/esm/module_map');
 const ModuleJob = require('internal/modules/esm/module_job');
 const createDynamicModule = require(
@@ -16,7 +16,7 @@ const jsonModuleDataUrl = 'data:application/json,""';
 const stubJsModule = createDynamicModule([], ['default'], jsModuleDataUrl);
 const stubJsonModule = createDynamicModule([], ['default'], jsonModuleDataUrl);
 
-const loader = new ESMLoader();
+const loader = createModuleLoader(false);
 const jsModuleJob = new ModuleJob(loader, stubJsModule.module, undefined,
                                   () => new Promise(() => {}));
 const jsonModuleJob = new ModuleJob(loader, stubJsonModule.module,
diff --git a/test/es-module/test-esm-loader-search.js b/test/es-module/test-esm-loader-search.js
index 0440d3d7775cff..3c451409b356db 100644
--- a/test/es-module/test-esm-loader-search.js
+++ b/test/es-module/test-esm-loader-search.js
@@ -10,8 +10,8 @@ const {
   defaultResolve: resolve
 } = require('internal/modules/esm/resolve');
 
-assert.rejects(
-  resolve('target'),
+assert.throws(
+  () => resolve('target'),
   {
     code: 'ERR_MODULE_NOT_FOUND',
     name: 'Error',
diff --git a/test/es-module/test-esm-loader-with-syntax-error.mjs b/test/es-module/test-esm-loader-with-syntax-error.mjs
index 0ed995ad510ee7..02a96b5b9470a8 100644
--- a/test/es-module/test-esm-loader-with-syntax-error.mjs
+++ b/test/es-module/test-esm-loader-with-syntax-error.mjs
@@ -13,7 +13,7 @@ describe('ESM: loader with syntax error', { concurrency: true }, () => {
       path('print-error-message.js'),
     ]);
 
-    match(stderr, /SyntaxError:/);
+    match(stderr, /SyntaxError \[Error\]:/);
     ok(!stderr.includes('Bad command or file name'));
     notStrictEqual(code, 0);
   });
diff --git a/test/es-module/test-esm-resolve-type.mjs b/test/es-module/test-esm-resolve-type.mjs
index f594e56cf18510..7a0527ff59e554 100644
--- a/test/es-module/test-esm-resolve-type.mjs
+++ b/test/es-module/test-esm-resolve-type.mjs
@@ -37,16 +37,16 @@ try {
    * ensure that resolving by full path does not return the format
    * with the defaultResolver
    */
-  await Promise.all([
+  [
     [ '/es-modules/package-type-module/index.js', 'module' ],
     [ '/es-modules/package-type-commonjs/index.js', 'commonjs' ],
     [ '/es-modules/package-without-type/index.js', 'commonjs' ],
     [ '/es-modules/package-without-pjson/index.js', 'commonjs' ],
-  ].map(async ([ testScript, expectedType ]) => {
+  ].forEach(([ testScript, expectedType ]) => {
     const resolvedPath = path.resolve(fixtures.path(testScript));
-    const resolveResult = await resolve(url.pathToFileURL(resolvedPath));
+    const resolveResult = resolve(url.pathToFileURL(resolvedPath));
     assert.strictEqual(resolveResult.format, expectedType);
-  }));
+  });
 
   /**
    * create a test module and try to resolve it by module name.
@@ -85,7 +85,7 @@ try {
     fs.writeFileSync(script,
                      'export function esm-resolve-tester() {return 42}');
 
-    const resolveResult = await resolve(`${moduleName}`);
+    const resolveResult = resolve(`${moduleName}`);
     assert.strictEqual(resolveResult.format, expectedResolvedType);
 
     fs.rmSync(nmDir, { recursive: true, force: true });
@@ -168,14 +168,14 @@ try {
     );
 
     // test the resolve
-    const resolveResult = await resolve(`${moduleName}`);
+    const resolveResult = resolve(`${moduleName}`);
     assert.strictEqual(resolveResult.format, 'module');
     assert.ok(resolveResult.url.includes('my-dual-package/es/index.js'));
   }
 
   // TestParameters are ModuleName, mainRequireScript, mainImportScript,
   // mainPackageType, subdirPkgJsonType, expectedResolvedFormat, mainSuffix
-  await Promise.all([
+  [
     [ 'mjs-mod-mod', 'index.js', 'index.mjs', 'module', 'module', 'module'],
     [ 'mjs-com-com', 'idx.js', 'idx.mjs', 'commonjs', 'commonjs', 'module'],
     [ 'mjs-mod-com', 'index.js', 'imp.mjs', 'module', 'commonjs', 'module'],
@@ -186,7 +186,7 @@ try {
     [ 'hmod', 'index.js', 'imp.js', 'commonjs', 'module', 'module', '#Key'],
     [ 'qhmod', 'index.js', 'imp.js', 'commonjs', 'module', 'module', '?k=v#h'],
     [ 'ts-mod-com', 'index.js', 'imp.ts', 'module', 'commonjs', undefined],
-  ].map(async (testVariant) => {
+  ].forEach((testVariant) => {
     const [
       moduleName,
       mainRequireScript,
@@ -234,10 +234,10 @@ try {
     );
 
     // test the resolve
-    const resolveResult = await resolve(`${moduleName}`);
+    const resolveResult = resolve(`${moduleName}`);
     assert.strictEqual(resolveResult.format, expectedResolvedFormat);
     assert.ok(resolveResult.url.endsWith(`${moduleName}/subdir/${mainImportScript}${mainSuffix}`));
-  }));
+  });
 
 } finally {
   process.chdir(previousCwd);
diff --git a/test/fixtures/es-module-loaders/hooks-input.mjs b/test/fixtures/es-module-loaders/hooks-input.mjs
index 6859cfc07d9b6a..5f61f679515040 100644
--- a/test/fixtures/es-module-loaders/hooks-input.mjs
+++ b/test/fixtures/es-module-loaders/hooks-input.mjs
@@ -2,6 +2,7 @@
 // node --loader ./test/fixtures/es-module-loaders/hooks-input.mjs ./test/fixtures/es-modules/json-modules.mjs
 
 import assert from 'assert';
+import { writeSync } from 'fs';
 import { readFile } from 'fs/promises';
 import { fileURLToPath } from 'url';
 
@@ -17,15 +18,12 @@ export async function resolve(specifier, context, next) {
     url = new URL(specifier).href;
     assert.match(specifier, /json-modules\.mjs$/);
     assert.strictEqual(context.parentURL, undefined);
-    assert.deepStrictEqual(context.importAssertions, {
-      __proto__: null,
-    });
+    assert.deepStrictEqual(context.importAssertions, {});
   } else if (resolveCalls === 2) {
     url = new URL(specifier, context.parentURL).href;
     assert.match(specifier, /experimental\.json$/);
     assert.match(context.parentURL, /json-modules\.mjs$/);
     assert.deepStrictEqual(context.importAssertions, {
-      __proto__: null,
       type: 'json',
     });
   }
@@ -45,7 +43,7 @@ export async function resolve(specifier, context, next) {
     shortCircuit: true,
   }
 
-  console.log(JSON.stringify(returnValue)); // For the test to validate when it parses stdout
+  writeSync(1, JSON.stringify(returnValue) + '\n'); // For the test to validate when it parses stdout
 
   return returnValue;
 }
@@ -57,14 +55,11 @@ export async function load(url, context, next) {
 
   if (loadCalls === 1) {
     assert.match(url, /json-modules\.mjs$/);
-    assert.deepStrictEqual(context.importAssertions, {
-      __proto__: null,
-    });
+    assert.deepStrictEqual(context.importAssertions, {});
     format = 'module';
   } else if (loadCalls === 2) {
     assert.match(url, /experimental\.json$/);
     assert.deepStrictEqual(context.importAssertions, {
-      __proto__: null,
       type: 'json',
     });
     format = 'json';
@@ -85,7 +80,7 @@ export async function load(url, context, next) {
     shortCircuit: true,
   };
 
-  console.log(JSON.stringify(returnValue)); // For the test to validate when it parses stdout
+  writeSync(1, JSON.stringify(returnValue) + '\n'); // For the test to validate when it parses stdout
 
   return returnValue;
 }
diff --git a/test/fixtures/es-module-loaders/loader-edge-cases.mjs b/test/fixtures/es-module-loaders/loader-edge-cases.mjs
index f50df0988194e4..19af0e2bc078c0 100644
--- a/test/fixtures/es-module-loaders/loader-edge-cases.mjs
+++ b/test/fixtures/es-module-loaders/loader-edge-cases.mjs
@@ -1,15 +1,13 @@
 import { strictEqual } from "node:assert";
 import { isMainThread, workerData, parentPort } from "node:worker_threads";
 
-// TODO(aduh95): switch this to `false` when loader hooks are run on a separate thread.
-strictEqual(isMainThread, true);
+strictEqual(isMainThread, false);
 
 // We want to make sure that internals are not leaked on the public module:
 strictEqual(workerData, null);
 strictEqual(parentPort, null);
 
-// TODO(aduh95): switch to `"undefined"` when loader hooks are run on a separate thread.
 // We don't want `import.meta.resolve` being available from loaders
 // as the sync implementation is not compatible with calling async
 // functions on the same thread.
-strictEqual(typeof import.meta.resolve, 'function');
+strictEqual(typeof import.meta.resolve, 'undefined');
diff --git a/test/fixtures/es-module-loaders/loader-load-foo-or-42.mjs b/test/fixtures/es-module-loaders/loader-load-foo-or-42.mjs
index 8f850e82bef54b..285b81a910ef5d 100644
--- a/test/fixtures/es-module-loaders/loader-load-foo-or-42.mjs
+++ b/test/fixtures/es-module-loaders/loader-load-foo-or-42.mjs
@@ -3,7 +3,7 @@ export async function load(url, context, next) {
   // resolution from follow-up loaders. It wouldn't be a problem
   // in real life because loaders aren't supposed to break the
   // resolution, but the ones used in our tests do, for convenience.
-  if (url.includes('loader')) {
+  if (url === 'node:fs' || url.includes('loader')) {
     return next(url);
   }
 
diff --git a/test/fixtures/es-module-loaders/loader-load-incomplete.mjs b/test/fixtures/es-module-loaders/loader-load-incomplete.mjs
index a4bf3531f3d225..bf6d5ea254dcc6 100644
--- a/test/fixtures/es-module-loaders/loader-load-incomplete.mjs
+++ b/test/fixtures/es-module-loaders/loader-load-incomplete.mjs
@@ -3,7 +3,7 @@ export async function load(url, context, next) {
   // resolution from follow-up loaders. It wouldn't be a problem
   // in real life because loaders aren't supposed to break the
   // resolution, but the ones used in our tests do, for convenience.
-  if (url.includes('loader')) {
+  if (url === 'node:fs' || url.includes('loader')) {
     return next(url);
   }
 
diff --git a/test/fixtures/es-module-loaders/loader-load-passthru.mjs b/test/fixtures/es-module-loaders/loader-load-passthru.mjs
index 1c2f2ea4487cdf..22fd7b0413aac8 100644
--- a/test/fixtures/es-module-loaders/loader-load-passthru.mjs
+++ b/test/fixtures/es-module-loaders/loader-load-passthru.mjs
@@ -1,12 +1,15 @@
+import { writeSync } from 'node:fs';
+
+
 export async function load(url, context, next) {
   // This check is needed to make sure that we don't prevent the
   // resolution from follow-up loaders. It wouldn't be a problem
   // in real life because loaders aren't supposed to break the
   // resolution, but the ones used in our tests do, for convenience.
-  if (url.includes('loader')) {
+  if (url === 'node:fs' || url.includes('loader')) {
     return next(url);
   }
 
-  console.log('load passthru'); // This log is deliberate
+  writeSync(1, 'load passthru' + '\n'); // Signal that this specific hook ran
   return next(url);
 }
diff --git a/test/fixtures/es-module-loaders/loader-load-receiving-modified-context.mjs b/test/fixtures/es-module-loaders/loader-load-receiving-modified-context.mjs
index 2d7bc350bd8775..6e5a1ee7193652 100644
--- a/test/fixtures/es-module-loaders/loader-load-receiving-modified-context.mjs
+++ b/test/fixtures/es-module-loaders/loader-load-receiving-modified-context.mjs
@@ -1,4 +1,7 @@
+import { writeSync } from 'node:fs';
+
+
 export async function load(url, context, next) {
-  console.log(context.foo); // This log is deliberate
+  writeSync(1, context.foo + '\n'); // Expose actual value the hook was called with
   return next(url, context);
 }
diff --git a/test/fixtures/es-module-loaders/loader-log-args.mjs b/test/fixtures/es-module-loaders/loader-log-args.mjs
index 84ed373d6b4de4..b56fddbce5854d 100644
--- a/test/fixtures/es-module-loaders/loader-log-args.mjs
+++ b/test/fixtures/es-module-loaders/loader-log-args.mjs
@@ -1,10 +1,13 @@
+import { writeSync } from 'node:fs';
+import { inspect } from 'node:util'
+
 export async function resolve(...args) {
-  console.log(`resolve arg count: ${args.length}`);
-  console.log({
+  writeSync(1, `resolve arg count: ${args.length}\n`);
+  writeSync(1, inspect({
     specifier: args[0],
     context: args[1],
     next: args[2],
-  });
+  }) + '\n');
 
   return {
     shortCircuit: true,
@@ -13,12 +16,12 @@ export async function resolve(...args) {
 }
 
 export async function load(...args) {
-  console.log(`load arg count: ${args.length}`);
-  console.log({
+  writeSync(1, `load arg count: ${args.length}\n`);
+  writeSync(1, inspect({
     url: args[0],
     context: args[1],
     next: args[2],
-  });
+  }) + '\n');
 
   return {
     format: 'module',
diff --git a/test/fixtures/es-module-loaders/loader-resolve-42.mjs b/test/fixtures/es-module-loaders/loader-resolve-42.mjs
index 05ef2f68390bd1..b571a27a9787e9 100644
--- a/test/fixtures/es-module-loaders/loader-resolve-42.mjs
+++ b/test/fixtures/es-module-loaders/loader-resolve-42.mjs
@@ -1,14 +1,17 @@
+import { writeSync } from 'node:fs';
+
+
 export async function resolve(specifier, context, next) {
   // This check is needed to make sure that we don't prevent the
   // resolution from follow-up loaders. It wouldn't be a problem
   // in real life because loaders aren't supposed to break the
   // resolution, but the ones used in our tests do, for convenience.
-  if (specifier.includes('loader')) {
+  if (specifier === 'node:fs' || specifier.includes('loader')) {
     return next(specifier);
   }
 
-  console.log('resolve 42'); // This log is deliberate
-  console.log('next<HookName>:', next.name); // This log is deliberate
+  writeSync(1, 'resolve 42' + '\n'); // Signal that this specific hook ran
+  writeSync(1, `next<HookName>: ${next.name}\n`); // Expose actual value the hook was called with
 
   return next('file:///42.mjs');
 }
diff --git a/test/fixtures/es-module-loaders/loader-resolve-foo.mjs b/test/fixtures/es-module-loaders/loader-resolve-foo.mjs
index 09d30e952a2a92..b5e5a419b99d45 100644
--- a/test/fixtures/es-module-loaders/loader-resolve-foo.mjs
+++ b/test/fixtures/es-module-loaders/loader-resolve-foo.mjs
@@ -1,12 +1,15 @@
+import { writeSync } from 'node:fs';
+
+
 export async function resolve(specifier, context, next) {
   // This check is needed to make sure that we don't prevent the
   // resolution from follow-up loaders. It wouldn't be a problem
   // in real life because loaders aren't supposed to break the
   // resolution, but the ones used in our tests do, for convenience.
-  if (specifier.includes('loader')) {
+  if (specifier === 'node:fs' || specifier.includes('loader')) {
     return next(specifier);
   }
 
-  console.log('resolve foo'); // This log is deliberate
+  writeSync(1, 'resolve foo' + '\n'); // Signal that this specific hook ran
   return next('file:///foo.mjs');
 }
diff --git a/test/fixtures/es-module-loaders/loader-resolve-incomplete.mjs b/test/fixtures/es-module-loaders/loader-resolve-incomplete.mjs
index d00b8fc50134e1..cb37a43527186c 100644
--- a/test/fixtures/es-module-loaders/loader-resolve-incomplete.mjs
+++ b/test/fixtures/es-module-loaders/loader-resolve-incomplete.mjs
@@ -3,7 +3,7 @@ export async function resolve(specifier, context, next) {
   // resolution from follow-up loaders. It wouldn't be a problem
   // in real life because loaders aren't supposed to break the
   // resolution, but the ones used in our tests do, for convenience.
-  if (specifier.includes('loader')) {
+  if (specifier === 'node:fs' || specifier.includes('loader')) {
     return next(specifier);
   }
 
diff --git a/test/fixtures/es-module-loaders/loader-resolve-next-modified.mjs b/test/fixtures/es-module-loaders/loader-resolve-next-modified.mjs
index ac5ad5b1fe020d..a6b8e85455d31c 100644
--- a/test/fixtures/es-module-loaders/loader-resolve-next-modified.mjs
+++ b/test/fixtures/es-module-loaders/loader-resolve-next-modified.mjs
@@ -3,7 +3,7 @@ export async function resolve(url, context, next) {
   // resolution from follow-up loaders. It wouldn't be a problem
   // in real life because loaders aren't supposed to break the
   // resolution, but the ones used in our tests do, for convenience.
-  if (url.includes('loader')) {
+  if (url === 'node:fs' || url.includes('loader')) {
     return next(url);
   }
 
diff --git a/test/fixtures/es-module-loaders/loader-resolve-passthru.mjs b/test/fixtures/es-module-loaders/loader-resolve-passthru.mjs
index d4845acc9f5f71..3a313611eb3e83 100644
--- a/test/fixtures/es-module-loaders/loader-resolve-passthru.mjs
+++ b/test/fixtures/es-module-loaders/loader-resolve-passthru.mjs
@@ -1,12 +1,15 @@
+import { writeSync } from 'node:fs';
+
+
 export async function resolve(specifier, context, next) {
   // This check is needed to make sure that we don't prevent the
   // resolution from follow-up loaders. It wouldn't be a problem
   // in real life because loaders aren't supposed to break the
   // resolution, but the ones used in our tests do, for convenience.
-  if (specifier.includes('loader')) {
+  if (specifier === 'node:fs' || specifier.includes('loader')) {
     return next(specifier);
   }
 
-  console.log('resolve passthru'); // This log is deliberate
+  writeSync(1, 'resolve passthru' + '\n'); // Signal that this specific hook ran
   return next(specifier);
 }
diff --git a/test/fixtures/es-module-loaders/loader-resolve-receiving-modified-context.mjs b/test/fixtures/es-module-loaders/loader-resolve-receiving-modified-context.mjs
index 83aa83104e96e4..f6a8fdad53ece3 100644
--- a/test/fixtures/es-module-loaders/loader-resolve-receiving-modified-context.mjs
+++ b/test/fixtures/es-module-loaders/loader-resolve-receiving-modified-context.mjs
@@ -1,4 +1,7 @@
+import { writeSync } from 'node:fs';
+
+
 export async function resolve(specifier, context, next) {
-  console.log(context.foo); // This log is deliberate
+  writeSync(1, context.foo + '\n'); // Expose actual value the hook was called with
   return next(specifier, context);
 }
diff --git a/test/fixtures/es-module-loaders/loader-resolve-shortcircuit.mjs b/test/fixtures/es-module-loaders/loader-resolve-shortcircuit.mjs
index e1a357b4ab48f9..00c18e75e2c7c5 100644
--- a/test/fixtures/es-module-loaders/loader-resolve-shortcircuit.mjs
+++ b/test/fixtures/es-module-loaders/loader-resolve-shortcircuit.mjs
@@ -3,7 +3,7 @@ export async function resolve(specifier, context, next) {
   // resolution from follow-up loaders. It wouldn't be a problem
   // in real life because loaders aren't supposed to break the
   // resolution, but the ones used in our tests do, for convenience.
-  if (specifier.includes('loader')) {
+  if (specifier === 'node:fs' || specifier.includes('loader')) {
     return next(specifier);
   }
 
diff --git a/test/fixtures/es-module-loaders/loader-resolve-strip-xxx.mjs b/test/fixtures/es-module-loaders/loader-resolve-strip-xxx.mjs
index 58d7a1107994fe..996dfd041c0df6 100644
--- a/test/fixtures/es-module-loaders/loader-resolve-strip-xxx.mjs
+++ b/test/fixtures/es-module-loaders/loader-resolve-strip-xxx.mjs
@@ -1,4 +1,10 @@
+import { writeSync } from 'node:fs';
+import { inspect } from 'node:util';
+
 export async function resolve(specifier, context, nextResolve) {
-  console.log(`loader-a`, {specifier});
+  if (specifier.startsWith('node:')) {
+    return nextResolve(specifier);
+  }
+  writeSync(1, `loader-a ${inspect({specifier})}\n`);
   return nextResolve(specifier.replace(/^xxx\//, `./`));
 }
diff --git a/test/fixtures/es-module-loaders/loader-resolve-strip-yyy.mjs b/test/fixtures/es-module-loaders/loader-resolve-strip-yyy.mjs
index 3615926143c4c7..7746469bf817eb 100644
--- a/test/fixtures/es-module-loaders/loader-resolve-strip-yyy.mjs
+++ b/test/fixtures/es-module-loaders/loader-resolve-strip-yyy.mjs
@@ -1,4 +1,7 @@
+import { writeSync } from 'node:fs';
+import { inspect } from 'node:util';
+
 export async function resolve(specifier, context, nextResolve) {
-  console.log(`loader-b`, {specifier});
+  writeSync(1, `loader-b ${inspect({specifier})}\n`);
   return nextResolve(specifier.replace(/^yyy\//, `./`));
 }
diff --git a/test/fixtures/es-module-loaders/never-settling-resolve-step/import.meta.never-resolve.mjs b/test/fixtures/es-module-loaders/never-settling-resolve-step/import.meta.never-resolve.mjs
index 51205a9475889c..fc3a077abe6ddc 100644
--- a/test/fixtures/es-module-loaders/never-settling-resolve-step/import.meta.never-resolve.mjs
+++ b/test/fixtures/es-module-loaders/never-settling-resolve-step/import.meta.never-resolve.mjs
@@ -1,5 +1,5 @@
 console.log('should be output');
 
-await import.meta.resolve('never-settle-resolve');
+import.meta.resolve('never-settle-resolve');
 
 console.log('should not be output');
diff --git a/test/fixtures/es-modules/import-resolve-exports.mjs b/test/fixtures/es-modules/import-resolve-exports.mjs
index 0bbce4fbc5efc0..e6a840ec996d96 100644
--- a/test/fixtures/es-modules/import-resolve-exports.mjs
+++ b/test/fixtures/es-modules/import-resolve-exports.mjs
@@ -1,10 +1,4 @@
 import { strictEqual } from 'assert';
 
-(async () => {
-  const resolved = await import.meta.resolve('pkgexports-sugar');
-  strictEqual(typeof resolved, 'string');
-})()
-.catch((e) => {
-  console.error(e);
-  process.exit(1);
-});
+const resolved = import.meta.resolve('pkgexports-sugar');
+strictEqual(typeof resolved, 'string');
diff --git a/test/fixtures/es-modules/runmain.mjs b/test/fixtures/es-modules/runmain.mjs
index 5ceb86b66c76ce..ee71ff42a81368 100644
--- a/test/fixtures/es-modules/runmain.mjs
+++ b/test/fixtures/es-modules/runmain.mjs
@@ -1,7 +1,7 @@
 import { runMain } from 'node:module';
 
-try { await import.meta.resolve('doesnt-matter.mjs') } catch {}
+try { import.meta.resolve('doesnt-matter.mjs') } catch {}
 
 runMain();
 
-try { await import.meta.resolve('doesnt-matter.mjs') } catch {}
+try { import.meta.resolve('doesnt-matter.mjs') } catch {}