esm: propagate process.exit from the loader thread to the main thread

lib/internal/modules/esm/hooks.js

@@ -503,6 +503,7 @@ class HooksProxy {
       },
     });
     this.#worker.unref(); // ! Allows the process to eventually exit.
+    this.#worker.on('exit', process.exit);
   }
 
   #waitForWorker() {
@@ -512,6 +513,7 @@ class HooksProxy {
         debug('wait for signal from worker');
         AtomicsWait(this.#lock, WORKER_TO_MAIN_THREAD_NOTIFICATION, 0);
         const response = this.#worker.receiveMessageSync();
+        if (response.message.status === 'exit') { return; }
         const { preloadScripts } = this.#unwrapMessage(response);
         this.#executePreloadScripts(preloadScripts);
       }
@@ -592,6 +594,8 @@ class HooksProxy {
     debug('got sync response from worker', { method, args });
     if (response.message.status === 'never-settle') {
       process.exit(kUnfinishedTopLevelAwait);
+    } else if (response.message.status === 'exit') {
+      process.exit(response.message.body);
     }
     return this.#unwrapMessage(response);
   }

lib/internal/modules/esm/worker.js

@@ -66,6 +66,19 @@ async function customizedModuleWorker(lock, syncCommPort, errorHandler) {
   let hooks, preloadScripts, initializationError;
   let hasInitializationError = false;
 
+  {
+    // If a custom hook is calling `process.exit`, we should wake up the main thread
+    // so it can detect the exit event.
+    const { exit } = process;
+    process.exit = function(code) {
+      syncCommPort.postMessage(wrapMessage('exit', code ?? process.exitCode));
+      AtomicsAdd(lock, WORKER_TO_MAIN_THREAD_NOTIFICATION, 1);
+      AtomicsNotify(lock, WORKER_TO_MAIN_THREAD_NOTIFICATION);
+      return ReflectApply(exit, this, arguments);
+    };
+  }
+
+
   try {
     initializeESM();
     const initResult = await initializeHooks();

test/es-module/test-esm-loader-hooks.mjs

@@ -195,4 +195,52 @@ describe('Loader hooks', { concurrency: true }, () => {
     assert.strictEqual(code, 0);
     assert.strictEqual(signal, null);
   });
+
+  it('should be fine to call `process.exit` from a custom async hook', async () => {
+    const { code, signal, stdout, stderr } = await spawnPromisified(execPath, [
+      '--no-warnings',
+      '--experimental-import-meta-resolve',
+      '--experimental-loader',
+      'data:text/javascript,export function load(a,b,next){if(a==="data:exit")process.exit(42);return next(a,b)}',
+      '--input-type=module',
+      '--eval',
+      'import "data:exit"',
+    ]);
+
+    assert.strictEqual(stderr, '');
+    assert.strictEqual(stdout, '');
+    assert.strictEqual(code, 42);
+    assert.strictEqual(signal, null);
+  });
+
+  it('should be fine to call `process.exit` from a custom sync hook', async () => {
+    const { code, signal, stdout, stderr } = await spawnPromisified(execPath, [
+      '--no-warnings',
+      '--experimental-import-meta-resolve',
+      '--experimental-loader',
+      'data:text/javascript,export function resolve(a,b,next){if(a==="exit:")process.exit(42);return next(a,b)}',
+      '--input-type=module',
+      '--eval',
+      'import "data:text/javascript,import.meta.resolve(%22exit:%22)"',
+    ]);
+
+    assert.strictEqual(stderr, '');
+    assert.strictEqual(stdout, '');
+    assert.strictEqual(code, 42);
+    assert.strictEqual(signal, null);
+  });
+
+  it('should be fine to call `process.exit` from the loader thread top-level', async () => {
+    const { code, signal, stdout, stderr } = await spawnPromisified(execPath, [
+      '--no-warnings',
+      '--experimental-loader',
+      'data:text/javascript,process.exit(42)',
+      fixtures.path('empty.js'),
+    ]);
+
+    assert.strictEqual(stderr, '');
+    assert.strictEqual(stdout, '');
+    assert.strictEqual(code, 42);
+    assert.strictEqual(signal, null);
+  });
 });