Emacs 26 - Threads and conditional variables example

elisp26-condvars.el

;; Unset var1
(setq var1 nil)

;; Create a mutex and an associated conditional variable
(setq mut1 (make-mutex "mut1"))
(setq cond-var1 (make-condition-variable mut1 "cond-var1"))

;; Read and set functions used by r1 and s1 threads
(defun read-global-var1 ()
  (with-mutex mut1
    (while (not var1)
      (message "var1 still not been set ... looping")
      ;; condition-wait is a blocking function. The thread will block here.
      (condition-wait cond-var1))
    (concat (message "var1 has been set ... exiting") var1)))

(defun set-global-var1 ()
  (with-mutex mut1
    (progn
      (sleep-for 5)
      (setq var1 "1")
      (condition-notify cond-var1))))

;; Create and start r1 thread
(make-thread 'read-global-var1 "r1")
(all-threads)

;; Create and start s1
(make-thread 'set-global-var1  "s1")
(all-threads)