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Re: frames vs. weak hash tables and garbage collection
From: |
Joe Wells |
Subject: |
Re: frames vs. weak hash tables and garbage collection |
Date: |
Fri, 28 Sep 2007 19:48:22 +0100 |
User-agent: |
Gnus/5.11 (Gnus v5.11) Emacs/22.1 (gnu/linux) |
Stefan Monnier <monnier@iro.umontreal.ca> writes:
>>> The reference from `values' is just due to the fact that you run
>>> `reproduce-bug' from M-: and that its return value contains the frame, so
>>> it's a rather unusual circumstance.
>
>> I'm confused. The frame can only show up in values if it fails to be
>> garbage collected for another reason.
>
> Right. In your case the reason is the recent events array.
>
>> Anyway, although I can see that the recent events array would be
>> enough to cause the problem, I'm not sure it is the only cause.
>
> Could be, but at least it matched the behavior I saw:
> if I hit a key 300 times, set `values' to nil, and call garbage-collect then
> the hash-table entry gets deleted (I modified your test case to make the
> hash-table global).
>
>> (defun reproduce-bug ()
>> [ ... new version of code deleted ... ]
>> ... )
>
> No idea about this one, but it may very well be due to transient effects
> such as the fact that the stack is scanned conservatively, so there may
> still be a spurious pointer to the frame left over somewhere at the time you
> call `garbage-collect'.
It seems it is not the stack. See below.
> Also the sit-for is enough to cause redisplay and execution of process
> filters, but I'm not convinced it's enough to cause the frame events to be
> added to the "recent events array", so maybe these will appear after the
> call to clear-this-command-keys.
Okay. Using a recursive-edit seems to be enough:
(defun reproduce-bug ()
(let ((ht (make-hash-table :weakness 'key)))
(let ((x
(make-frame)
;;(get-buffer-create "xyzzy")
))
(puthash x t ht)
(delete-frame x)
;;(kill-buffer x)
)
;; Give time for various frame related events to be handled, in
;; case this is needed.
(recursive-edit)
;; There may be a reference to the frame in the array of recent
;; events, so we clear this array.
(clear-this-command-keys)
;; In theory, the only reference to the new frame is now the key
;; in the hash table. Because of the weakness, this key should
;; not keep the frame alive.
(garbage-collect)
;; The hash table should now be empty.
(let (l)
(maphash (lambda (k v) (push (cons k v) l)) ht)
l)))
Evaluate (reproduce-bug) and type C-M-c (exit-recursive-edit) in the
recursive edit, and it correctly returns nil.
(By the way, I tried doing
(setq unread-command-events (append (kbd "C-M-c") nil))
just before the recursive edit, but that wasn't enough. It needs to
have real user interaction. I'm curious if there is some purely
programmatic way of simulating the effects of a recursive edit with
only C-M-c typed in it, because this would help in building test
cases.)
Conclusion: There is no bug with garbage collection of deleted
frames, but merely the appearance of a bug, because the recent event
array keeps the frame alive for a while.
Thanks for tracking down the cause of the appearance of a bug!
--
Joe
- Re: frames vs. weak hash tables and garbage collection, (continued)
- Re: frames vs. weak hash tables and garbage collection, Thien-Thi Nguyen, 2007/09/01
- Re: frames vs. weak hash tables and garbage collection, Joe Wells, 2007/09/25
- Re: frames vs. weak hash tables and garbage collection, Glenn Morris, 2007/09/27
- Re: frames vs. weak hash tables and garbage collection, Thien-Thi Nguyen, 2007/09/27
- Re: frames vs. weak hash tables and garbage collection, Richard Stallman, 2007/09/27
- Message not available
- Re: frames vs. weak hash tables and garbage collection, Stefan Monnier, 2007/09/28
- Re: frames vs. weak hash tables and garbage collection, Joe Wells, 2007/09/28
- Re: frames vs. weak hash tables and garbage collection, Stefan Monnier, 2007/09/28
- Re: frames vs. weak hash tables and garbage collection, Joe Wells, 2007/09/28
- Re: frames vs. weak hash tables and garbage collection, Stefan Monnier, 2007/09/28
- Re: frames vs. weak hash tables and garbage collection,
Joe Wells <=
- Re: frames vs. weak hash tables and garbage collection, Richard Stallman, 2007/09/29
- Re: frames vs. weak hash tables and garbage collection, Joe Wells, 2007/09/29
- Re: frames vs. weak hash tables and garbage collection, Stefan Monnier, 2007/09/29
- RE: frames vs. weak hash tables and garbage collection, Drew Adams, 2007/09/29
- Re: frames vs. weak hash tables and garbage collection, Richard Stallman, 2007/09/30