Channel Synchronization in Racket

Our example demonstrates how to synchronize execution across different threads in Racket. We’ll use channels to wait for a thread to finish its work. When waiting for multiple threads to finish, you might prefer to use a semaphore or a condition variable.

#lang racket

(require racket/async-channel)

; 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)
  (displayln "done")
  ; Send a value to notify that we're done.
  (async-channel-put done-channel #t))

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

(main)

To run the program:

$ racket channel-synchronization.rkt
working...done

If you removed the (async-channel-get done) line from this program, the program would exit before the worker even started.

In this Racket version:

1. We use racket/async-channel to create asynchronous channels, which are similar to Go’s channels.
2. The worker function is defined to perform some work and then send a notification on the channel.
3. In the main function, we create an asynchronous channel, start a new thread running the worker function, and then wait for the notification from the worker.
4. We use thread to start a new thread, which is analogous to Go’s goroutines.
5. async-channel-put is used to send a value on the channel, and async-channel-get is used to receive a value, blocking until one is available.

This example demonstrates how Racket can be used for concurrent programming, using threads and channels for synchronization between them.