for the first problem, you've found a bug in the Racket CS thread
scheduler (i.e., Racket BC behaves correctly in this case). Suspending
a thread that is sleeping didn't prevent the thread from being woken up
on its previous schedule. I've pushed a repair as commit 7a12b4ac93.
After fixing that bug and using `thread/suspend-to-kill`, the second
part works as expected. But if `t1` is created with `thread`, the
behavior you describe sounds right: `t2` cannot resume a thread that
was created with `thread` and then terminated by a custodian.
Thanks for the report!
Matthew
At Sat, 7 Nov 2020 15:26:17 -0800 (PST), Greg Rosenblatt wrote:
> I'm experimenting with using custodians to manage threads (on Racket 7.8
> [cs]) and encountering behavior I don't understand.
>
> I start a looping thread `t1` under a new custodian `c1`.
>
> I then shutdown `c1` and expect `t1` to stop looping. If I started `t1`
> with `thread` then this expectation is met. However, if I start it with
> `thread/suspend-to-kill`, it continues looping even after `c1` is shut
> down. Is this the correct behavior?
>
> Additionally, I later start a new thread `t2` under a new custodian `c2`,
> which attempts to resume `t1` after the shutdown, using itself as a
> benefactor. However, `t1` does not seem to resume. Is this the correct
> behavior?
>
> Here is the code I'm working with:
>
> ```
> #lang racket
>
> (define c1 (make-custodian))
> (define c2 (make-custodian))
> (define t1 #f)
> (define t2 #f)
>
> (parameterize ((current-custodian c1))
> ;(set! t1 (thread/suspend-to-kill ;; (custodian-shutdown-all c1) fails
> to suspend this thread
> (set! t1 (thread
> (lambda ()
>(let loop ()
> (displayln "thread 1")
> (sleep 2)
> (loop))
>
> (displayln "ENTER to continue")
> (read-line)
>
> (custodian-shutdown-all c1)
>
> (displayln "ENTER to continue")
> (read-line)
>
> (parameterize ((current-custodian c2))
> (set! t2 (thread
> (lambda ()
>(thread-resume t1 (current-thread))
>(let loop ()
> (displayln "thread 2")
> (sleep 2)
> (loop))
>
> (displayln "ENTER to continue")
> (read-line)
>
> (custodian-shutdown-all c2)
>
> (displayln "ENTER to continue")
> (read-line)
> ```
>
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