src: discard tasks posted to platform TaskRunner during shutdown

Discard tasks silently that are posted when the Isolate is being disposed. It is not possible to avoid a race condition window between unregistering the Isolate with the platform and disposing it in which background tasks and the Isolate deinit steps themselves may lead to new tasks being posted. The only sensible action in that case is discarding the tasks. Fixes: #31752 Fixes: https://bugs.chromium.org/p/v8/issues/detail?id=10104 Refs: https://chromium-review.googlesource.com/c/v8/v8/+/2061548 Refs: #31795 Refs: #30909 PR-URL: #31853 Reviewed-By: Joyee Cheung <[email protected]>

Author: addaleax

src/node_platform.cc

@@ -239,14 +239,22 @@ void PerIsolatePlatformData::PostIdleTask(std::unique_ptr<v8::IdleTask> task){
 }
 
 voidPerIsolatePlatformData::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_);
 }
 
 voidPerIsolatePlatformData::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(newDelayedTask());
  delayed->task = std::move(task);
  delayed->platform_data = shared_from_this();