vm: add experimental NodeRealm implementation

LICENSE

@@ -2186,3 +2186,28 @@ The externally maintained libraries used by Node.js are:
     NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
     SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   """
+
+- synchronous-worker, located at lib/internal/vm/localworker.js, is licensed as follows:
+  """
+    The MIT License (MIT)
+
+    Copyright (c) 2020 Anna Henningsen
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in all
+    copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+    SOFTWARE.
+  """

doc/api/cli.md

@@ -530,6 +530,22 @@ changes:
 Specify the `module` of a custom experimental [ECMAScript module loader][].
 `module` may be any string accepted as an [`import` specifier][].
 
+### `--experimental-localworker`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+Enable experimental support for `vm.LocalWorker`.
+
+### `--no-experimental-localworker`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+Disable experimental support for `vm.LocalWorker`.
+
 ### `--experimental-network-imports`
 
 <!-- YAML
@@ -2113,6 +2129,7 @@ Node.js options that are allowed are:
 * `--experimental-import-meta-resolve`
 * `--experimental-json-modules`
 * `--experimental-loader`
+* `--experimental-localworker`
 * `--experimental-modules`
 * `--experimental-network-imports`
 * `--experimental-permission`

doc/api/vm.md

@@ -1573,6 +1573,105 @@ inside a `vm.Context`, functions passed to them will be added to global queues,
 which are shared by all contexts. Therefore, callbacks passed to those functions
 are not controllable through the timeout either.
 
+## Local Worker
+
+> Stability: 1 - Experimental
+
+### Class: `LocalWorker`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* Extends: {EventEmitter}
+
+A `LocalWorker` is effectively a Node.js environment that runs within the
+same thread.
+
+```mjs
+import { LocalWorker } from 'vm';
+import { fileURLToPath } from 'url';
+const w = new LocalWorker();
+const myAsyncFunction = w.createRequire(fileURLToPath(import.meta.url))('my-module');
+console.log(await myAsyncFunction());
+```
+
+#### `new LocalWorker()`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+#### `localworker.runInWorkerScope(fn)`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* `fn` {Function}
+
+Wrap `fn` and run it as if it were run on the event loop of the inner Node.js
+instance. In particular, this ensures that Promises created by the function
+itself are resolved correctly. You should generally use this to run any code
+inside the inner Node.js instance that performs asynchronous activity and that
+is not already running in an asynchronous context (you can compare this to
+the code that runs synchronously from the main file of a Node.js application).
+
+#### `localworker.stop()`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+This will render the Node.js instance unusable
+and is generally comparable to running `process.exit()`.
+
+This method returns a `Promise` that will be resolved when all resources
+associated with this Node.js instance are released. This `Promise` resolves on
+the event loop of the _outer_ Node.js instance.
+
+#### `localworker.createRequire(filename)`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* `filename` {string}
+
+Create a `require()` function that can be used for loading CommonJS modules
+inside the inner Node.js instance.
+
+#### `localworker.createImport(filename)`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* `filename` {string}
+
+Create a dynamic `import()` function that can be used for loading EcmaScript
+modules inside the inner Node.js instance.
+
+#### `localworker.globalThis`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* Type: {Object}
+
+Returns a reference to the global object of the inner Node.js instance.
+
+#### `localworker.process`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* Type: {Object}
+
+Returns a reference to the `process` object of the inner Node.js instance.
+
 [Cyclic Module Record]: https://tc39.es/ecma262/#sec-cyclic-module-records
 [ECMAScript Module Loader]: esm.md#modules-ecmascript-modules
 [Evaluate() concrete method]: https://tc39.es/ecma262/#sec-moduleevaluation

lib/internal/process/pre_execution.js

@@ -67,6 +67,7 @@ function prepareExecution(options) {
   setupInspectorHooks();
   setupWarningHandler();
   setupFetch();
+  setupLocalWorker();
   setupWebCrypto();
   setupCustomEvent();
   setupCodeCoverage();
@@ -267,6 +268,16 @@ function setupFetch() {
   });
 }
 
+function setupLocalWorker() {
+  // Patch the vm module when --experimental-localworker is on.
+  // Please update the comments in vm.js when this block changes.
+  if (getOptionValue('--experimental-localworker')) {
+    const LocalWorker = require('internal/vm/localworker');
+    const vm = require('vm');
+    vm.LocalWorker = LocalWorker;
+  }
+}
+
 // TODO(aduh95): move this to internal/bootstrap/web/* when the CLI flag is
 //               removed.
 function setupWebCrypto() {

lib/internal/vm/localworker.js

@@ -0,0 +1,141 @@
+'use strict';
+
+// LocalWorker was originally a separate module developed by
+// Anna Henningsen and published separately on npm as the
+// synchronous-worker module under the MIT license. It has been
+// incorporated into Node.js with Anna's permission.
+// See the LICENSE file for LICENSE and copyright attribution.
+
+const {
+  Promise,
+} = primordials;
+
+const {
+  LocalWorker: LocalWorkerImpl,
+} = internalBinding('contextify');
+
+const EventEmitter = require('events');
+const { setTimeout } = require('timers');
+const { dirname, join } = require('path');
+
+let debug = require('internal/util/debuglog').debuglog('localworker', (fn) => {
+  debug = fn;
+});
+
+class LocalWorker extends EventEmitter {
+  #handle = undefined;
+  #process = undefined;
+  #global = undefined;
+  #module = undefined;
+  #stoppedPromise = undefined;
+  /**
+   */
+  constructor() {
+    super();
+    this.#handle = new LocalWorkerImpl();
+    this.#handle.onexit = (code) => {
+      this.stop();
+      this.emit('exit', code);
+    };
+    try {
+      this.#handle.start();
+      this.#handle.load((process, nativeRequire, globalThis) => {
+        this.#process = process;
+        this.#module = nativeRequire('module');
+        this.#global = globalThis;
+        process.on('uncaughtException', (err) => {
+          if (process.listenerCount('uncaughtException') === 1) {
+            this.emit('error', err);
+            process.exit(1);
+          }
+        });
+      });
+    } catch (err) {
+      this.#handle.stop();
+      throw err;
+    }
+  }
+
+  /**
+   * @returns {Promise<void>}
+   */
+  async stop() {
+    // TODO(@mcollina): add support for AbortController, we want to abort this,
+    // or add a timeout.
+    return this.#stoppedPromise ??= new Promise((resolve) => {
+      const onExit = () => {
+        debug('stopping localworker');
+        this.#handle.stop();
+        resolve();
+      };
+
+      const tryClosing = () => {
+        const closed = this.#handle.tryCloseAllHandles();
+        debug('closed %d handles', closed);
+        if (closed > 0) {
+          // This is an active wait for the handles to close.
+          // We might want to change this in the future to use a callback,
+          // but at this point it seems like a premature optimization.
+          // TODO(@mcollina): refactor to use a close callback
+          setTimeout(tryClosing, 100);
+        } else {
+          this.#handle.signalStop();
+
+          setTimeout(onExit, 100);
+        }
+      };
+
+      // We use setTimeout instead of setImmediate because it runs in a different
+      // phase of the event loop. This is important because the immediate queue
+      // would crash if the environment it refers to has been already closed.
+      setTimeout(tryClosing, 100);
+    });
+  }
+
+  get process() {
+    return this.#process;
+  }
+
+  get globalThis() {
+    return this.#global;
+  }
+
+  createRequire(...args) {
+    return this.#module.createRequire(...args);
+  }
+
+  /**
+   * @param {() => any} method
+   */
+  runInWorkerScope(method) {
+    return this.#handle.runInCallbackScope(method);
+  }
+
+  /**
+   * @param {string} filename
+   */
+  async createImport(filename) {
+    // This is a hack to get around creating a dynamic import function
+    // from code. We create a temporary file that exports the import
+    // function, and then delete it.
+    // TODO(@mcollina): figure out how to do this using internal APIs.
+
+    const req = this.createRequire(filename);
+    const fs = req('fs/promises');
+
+    const sourceText = `
+      module.exports = (file) => import(file);
+    `;
+
+    const dest = join(dirname(filename), `_import_jump_${process.pid}.js`);
+    await fs.writeFile(dest, sourceText);
+
+    const ownImport = req(dest);
+
+    await fs.unlink(dest);
+
+    return ownImport;
+  }
+}
+
+module.exports = LocalWorker;

lib/vm.js

@@ -343,3 +343,5 @@ module.exports = {
 // The vm module is patched to include vm.Module, vm.SourceTextModule
 // and vm.SyntheticModule in the pre-execution phase when
 // --experimental-vm-modules is on.
+// The vm module is also patched to include vm.LocalWorker in the
+// pre-execution phase when --experimental-localworker is on.

src/env_properties.h

@@ -366,6 +366,7 @@
   V(socketaddress_constructor_template, v8::FunctionTemplate)                  \
   V(streambaseentry_ctor_template, v8::FunctionTemplate)                       \
   V(streambaseoutputstream_constructor_template, v8::ObjectTemplate)           \
+  V(localworker_constructor_template, v8::FunctionTemplate)                    \
   V(streamentry_ctor_template, v8::FunctionTemplate)                           \
   V(streamentry_opaque_ctor_template, v8::FunctionTemplate)                    \
   V(qlogoutputstream_constructor_template, v8::ObjectTemplate)                 \