Junk Drawer
For all those little papers scattered across your desk
Junk DrawerFor all those little papers scattered across your desk
I stand for the Constitution, for due process, and for community that takes care of each other.
Yes, Racket will collect as garbage a thread that is blocked on a channel that can have no writers (according to Matthew Flatt).
Matthew also suggested a nice refinement of my program below that demonstrates the effect. I’ll show his first:
#lang racket
;; store a weak reference to the thread, but make sure the channel has no
;; writers
(define t
(make-weak-box
(let ()
(define c (make-channel))
(thread (thunk (sync c))))))
;; The (sync (system-idle-evt)) will not return until the thread has run as far
;; as it can, at which point it's GC-able. (The system-idle-evt constructor
;; exists essentially only for this kind of test/example.)
(sync (system-idle-evt))
(collect-garbage)
(weak-box-value t) ;=> #f
My original version was:
#lang racket
;; store a weak reference to the thread, but make sure the channel has no
;; writers
(define t
(make-weak-box
(let ()
(define c (make-channel))
(thread (thunk (sync c))))))
;; wait for the GC to collect…
(let loop ()
(match (weak-box-value t)
[(? thread?)
;; …by forcing it (but not too aggressively)
(collect-garbage)
(loop)]
[#f (displayln "thread was GC'd")]))
It reliably prints and exits within a second or 2 on my machine.