Racket custodians and namespaces for rebootable racket programs

README.md

Demonstrates the use of Racket's custodians and namespaces to create enough isolation to "reboot" programs without restarting the whole of Racket, including possibly recompiling and reloading code.

To experiment with this:

$ racket ~/src/racket-experiments$ racket
Welcome to Racket v5.3.1.4.
-> (require "reloader.rkt")
-> (load-and-foo)
Starting worker...
test-mod: "foo"
other-mod: "foo"
other-mod: "foo"
other-mod: "foo"
other-mod: "foo"
Terminating worker...
-> 

Subsequent runs of (load-and-foo) will reload the code from scratch. If you've edited one of test-mod.rkt or other-mod.rkt in the meantime, the changes will show up.

Note that other-mod.rkt runs a loop "forever", but that reloader.rkt terminates all threads in the nested custodian.

other-mod.rkt

#lang racket/base

(require "test-mod.rkt")

(let loop ()
  (printf "other-mod: ~v\n" (foo))
  (sleep 1)
  (loop))

reloader.rkt

#lang racket/base

(define (load-and-foo)
  (define sub-custodian (make-custodian))
  (printf "Starting worker...\n")
  (parameterize ((current-custodian sub-custodian))
    (thread (lambda ()
        (parameterize ((current-namespace (make-base-namespace)))
		(dynamic-require "other-mod.rkt" #f)))))
  (sleep 3.5)
  (printf "Terminating worker...\n")
  (custodian-shutdown-all sub-custodian))

(provide load-and-foo)

test-mod.rkt

#lang racket/base

(provide foo)

(define (foo) "foo")

(printf "test-mod: ~v\n" (foo))

Following up... the "correct" way instead of a named anchor is to use make-gui-namespace instead of make-namespace... I'm gonna sprinkle this around since there are so few hits when searching for this problem.