Some CPU heavy operations like crypto are not put in a threadpool. While it may be running C code, it will block the main thread while executing. See https://gi

Some CPU heavy operations like crypto are not put in a threadpool. While it may be running C code, it will block the main thread while executing. See https://github.com/nodejs/node/issues/678 https://github.com/nodejs/node/issues/678 Perhaps the new worker threads may alleviate this, but I'm not sure (it's still an experimental API).