Please re-read the comment, thank you. In addition, there are single-threaded and thread-per-core executors with different future bounds. It is that Tokio puts

Please re-read the comment, thank you. In addition, there are single-threaded and thread-per-core executors with different future bounds. It is that Tokio puts more requirements on Send and Sync because it is a proper implementation with worker-per-core (configurable to be otherwise) + work stealing.