The Threading library Starting in Emacs 26 some very ambitious changes were added. Basic thread support was enabled, laying the groundwork for a future concurrent emacs. The docs layout this possibility: Emacs Lisp provides a limited form of concurrency, called threads. All the threads in a given instance of Emacs share the same memory. Concurrency in Emacs Lisp is “mostly cooperative”, meaning that Emacs will only switch execution between threads at well-defined times.