Channel Synchronization in Scheme

(import (rnrs) (rnrs control) (rnrs io simple))

;; This is the function we'll run in a separate thread. The
;; done-channel will be used to notify another thread that
;; this function's work is done.
(define (worker done-channel)
  (display "working...")
  (sleep 1)
  (display "done\n")
  ;; Send a value to notify that we're done.
  (channel-put! done-channel #t))

(define (main)
  ;; Start a worker thread, giving it the channel to
  ;; notify on.
  (let ((done-channel (make-channel)))
    (fork-thread (lambda () (worker done-channel)))
    
    ;; Block until we receive a notification from the
    ;; worker on the channel.
    (channel-get! done-channel)))

;; Run the main function
(main)

This Scheme code demonstrates channel synchronization, which is similar to the concept in the original example. Here’s a breakdown of the code:

1. We import necessary libraries for I/O operations and thread control.

2. The worker function simulates some work by displaying “working…”, sleeping for a second, and then displaying “done”. After completing its work, it sends a value through the done-channel to signal completion.

3. In the main function, we create a channel using make-channel.

4. We start a new thread using fork-thread and pass it an anonymous function that calls worker with the done-channel.

5. The main thread then waits for a value on the done-channel using channel-get!. This blocks until the worker thread sends a value, effectively synchronizing the two threads.

6. Finally, we call the main function to run our program.

To run this program, save it to a file (e.g., channel-synchronization.scm) and execute it with a Scheme interpreter that supports threads and channels (like Chez Scheme):

$ scheme --script channel-synchronization.scm
working...done

If you removed the (channel-get! done-channel) line from this program, the main thread would exit before the worker thread even started, potentially ending the program prematurely.

Note that the exact syntax and available functions may vary depending on the Scheme implementation you’re using. This example assumes an implementation with support for threads and channels.