sea: only assert snapshot main function for main threads

src/node.cc

@@ -320,7 +320,8 @@ MaybeLocal<Value> StartExecution(Environment* env, StartExecutionCallback cb) {
   CHECK(!env->isolate_data()->is_building_snapshot());
 
 #ifndef DISABLE_SINGLE_EXECUTABLE_APPLICATION
-  if (sea::IsSingleExecutable()) {
+  // Snapshot in SEA is only loaded for the main thread.
+  if (sea::IsSingleExecutable() && env->is_main_thread()) {
     sea::SeaResource sea = sea::FindSingleExecutableResource();
     // The SEA preparation blob building process should already enforce this,
     // this check is just here to guard against the unlikely case where
@@ -342,6 +343,9 @@ MaybeLocal<Value> StartExecution(Environment* env, StartExecutionCallback cb) {
   // move the pre-execution part into a different file that can be
   // reused when dealing with user-defined main functions.
   if (!env->snapshot_deserialize_main().IsEmpty()) {
+    // Custom worker snapshot is not supported yet,
+    // so workers can't have deserialize main functions.
+    CHECK(env->is_main_thread());
     return env->RunSnapshotDeserializeMain();
   }
 

test/sequential/test-single-executable-application-snapshot-worker.js

@@ -0,0 +1,80 @@
+'use strict';
+
+require('../common');
+
+const {
+  generateSEA,
+  skipIfSingleExecutableIsNotSupported,
+} = require('../common/sea');
+
+skipIfSingleExecutableIsNotSupported();
+
+// This tests the snapshot support in single executable applications.
+
+const tmpdir = require('../common/tmpdir');
+const { writeFileSync, existsSync } = require('fs');
+const {
+  spawnSyncAndAssert, spawnSyncAndExitWithoutError,
+} = require('../common/child_process');
+const assert = require('assert');
+
+const configFile = tmpdir.resolve('sea-config.json');
+const seaPrepBlob = tmpdir.resolve('sea-prep.blob');
+const outputFile = tmpdir.resolve(process.platform === 'win32' ? 'sea.exe' : 'sea');
+
+{
+  tmpdir.refresh();
+
+  // FIXME(joyeecheung): currently `worker_threads` cannot be loaded during the
+  // snapshot building process because internal/worker.js is accessing isMainThread at
+  // the top level (and there are maybe more code that access these at the top-level),
+  // and have to be loaded in the deserialized snapshot main function.
+  // Change these states to be accessed on-demand.
+  const code = `
+  const {
+    setDeserializeMainFunction,
+  } = require('v8').startupSnapshot;
+  setDeserializeMainFunction(() => {
+    const { Worker } = require('worker_threads');
+    new Worker("console.log('Hello from Worker')", { eval: true });
+  });
+  `;
+
+  writeFileSync(tmpdir.resolve('snapshot.js'), code, 'utf-8');
+  writeFileSync(configFile, `
+  {
+    "main": "snapshot.js",
+    "output": "sea-prep.blob",
+    "useSnapshot": true
+  }
+  `);
+
+  spawnSyncAndExitWithoutError(
+    process.execPath,
+    ['--experimental-sea-config', 'sea-config.json'],
+    {
+      cwd: tmpdir.path,
+      env: {
+        NODE_DEBUG_NATIVE: 'SEA',
+        ...process.env,
+      },
+    });
+
+  assert(existsSync(seaPrepBlob));
+
+  generateSEA(outputFile, process.execPath, seaPrepBlob);
+
+  spawnSyncAndAssert(
+    outputFile,
+    {
+      env: {
+        NODE_DEBUG_NATIVE: 'SEA',
+        ...process.env,
+      }
+    },
+    {
+      trim: true,
+      stdout: 'Hello from Worker'
+    }
+  );
+}