src: avoid draining platform tasks at FreeEnvironment

At the point of `FreeEnvironment` and onwards, no JavaScript execution
associated with the Environment should be triggered.

Avoid draining platform tasks that can trigger JavaScript execution in
`FreeEnvironment`. The holder of `node::Environment` should immediately
call `node::MultiIsolatePlatform::UnregisterIsolate` and
`v8::Isolate::Dispose` to cancel pending foreground tasks and join
concurrent tasks after the environment was freed.

`NodePlatform` can properly handle the case in `RunForegroundTask` when
an Isolate out-lives its associated `node::Environment`.

src/api/environment.cc

@@ -512,13 +512,6 @@ void FreeEnvironment(Environment* env) {
     RunAtExit(env);
   }
 
-  // This call needs to be made while the `Environment` is still alive
-  // because we assume that it is available for async tracking in the
-  // NodePlatform implementation.
-  MultiIsolatePlatform* platform = env->isolate_data()->platform();
-  if (platform != nullptr)
-    platform->DrainTasks(isolate);
-
   delete env;
 }
 

src/node_main_instance.cc

@@ -65,6 +65,13 @@ NodeMainInstance::~NodeMainInstance() {
   if (isolate_params_ == nullptr) {
     return;
   }
+
+#ifdef DEBUG
+  // node::Environment has been disposed and no JavaScript Execution is allowed
+  // at this point.
+  Isolate::DisallowJavascriptExecutionScope disallow_js(
+      isolate_, Isolate::DisallowJavascriptExecutionScope::CRASH_ON_FAILURE);
+#endif
   // This should only be done on a main instance that owns its isolate.
   // IsolateData must be freed before UnregisterIsolate() is called.
   isolate_data_.reset();

src/node_platform.cc

@@ -424,6 +424,11 @@ void PerIsolatePlatformData::RunForegroundTask(std::unique_ptr<Task> task) {
                                    InternalCallbackScope::kNoFlags);
     task->Run();
   } else {
+    // When the Environment was freed, the tasks of the Isolate should also be
+    // canceled by `NodePlatform::UnregisterIsolate`. However, if the embedder
+    // request to run the foreground task after the Environment was freed, run
+    // the task without InternalCallbackScope.
+
     // The task is moved out of InternalCallbackScope if env is not available.
     // This is a required else block, and should not be removed.
     // See comment: https://github.com/nodejs/node/pull/34688#pullrequestreview-463867489

test/parallel/test-finalization-registry-shutdown.js

@@ -0,0 +1,23 @@
+// Flags: --expose-gc
+'use strict';
+const common = require('../common');
+
+// This test verifies that when a V8 FinalizationRegistryCleanupTask is queue
+// at the last moment when JavaScript can be executed, the callback of a
+// FinalizationRegistry will not be invoked and the process should exit
+// normally.
+
+const reg = new FinalizationRegistry(
+  common.mustNotCall('This FinalizationRegistry callback should never be called'));
+
+function register() {
+  // Create a temporary object in a new function scope to allow it to be GC-ed.
+  reg.register({});
+}
+
+process.on('exit', () => {
+  // This is the final chance to execute JavaScript.
+  register();
+  // Queue a FinalizationRegistryCleanupTask by a testing gc request.
+  global.gc();
+});