src: discard tasks posted to platform TaskRunner during shutdown

src/node_main_instance.cc

@@ -102,12 +102,8 @@ NodeMainInstance::~NodeMainInstance() {
   if (!owns_isolate_) {
     return;
   }
-  // TODO(addaleax): Reverse the order of these calls. The fact that we first
-  // dispose the Isolate is a temporary workaround for
-  // https://github.com/nodejs/node/issues/31752 -- V8 should not be posting
-  // platform tasks during Dispose(), but it does in some WASM edge cases.
-  isolate_->Dispose();
   platform_->UnregisterIsolate(isolate_);
+  isolate_->Dispose();
 }
 
 int NodeMainInstance::Run() {

src/node_platform.cc

@@ -244,14 +244,22 @@ void PerIsolatePlatformData::PostIdleTask(std::unique_ptr<v8::IdleTask> task) {
 }
 
 void PerIsolatePlatformData::PostTask(std::unique_ptr<Task> task) {
-  CHECK_NOT_NULL(flush_tasks_);
+  if (flush_tasks_ == nullptr) {
+    // V8 may post tasks during Isolate disposal. In that case, the only
+    // sensible path forward is to discard the task.
+    return;
+  }
   foreground_tasks_.Push(std::move(task));
   uv_async_send(flush_tasks_);
 }
 
 void PerIsolatePlatformData::PostDelayedTask(
     std::unique_ptr<Task> task, double delay_in_seconds) {
-  CHECK_NOT_NULL(flush_tasks_);
+  if (flush_tasks_ == nullptr) {
+    // V8 may post tasks during Isolate disposal. In that case, the only
+    // sensible path forward is to discard the task.
+    return;
+  }
   std::unique_ptr<DelayedTask> delayed(new DelayedTask());
   delayed->task = std::move(task);
   delayed->platform_data = shared_from_this();