* Garbage collect and buffer-undo-list
@ 2021-03-13 18:17 Yuan Fu
2021-03-13 19:01 ` Stefan Monnier
0 siblings, 1 reply; 3+ messages in thread
From: Yuan Fu @ 2021-03-13 18:17 UTC (permalink / raw)
To: emacs-devel
I know the garbage collector trims buffer-undo-list. Does it collect the cons cell if there are other references to that object (other than buffer-undo-list)?
I tried this:
(setq last1 (last buffer-undo-list))
(garbage-collect)
After the garbage collection, the entry referred by last1 is not in buffer-undo-list anymore, but still accessible by last1. That seems to support my theory.
Yuan
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Garbage collect and buffer-undo-list
2021-03-13 18:17 Garbage collect and buffer-undo-list Yuan Fu
@ 2021-03-13 19:01 ` Stefan Monnier
2021-03-13 19:16 ` Yuan Fu
0 siblings, 1 reply; 3+ messages in thread
From: Stefan Monnier @ 2021-03-13 19:01 UTC (permalink / raw)
To: Yuan Fu; +Cc: emacs-devel
> I know the garbage collector trims buffer-undo-list. Does it collect the
> cons cell if there are other references to that object (other than
> buffer-undo-list)?
No, it can't.
If you want to keep a reference to some of those cons-cells but still
want the GC to collect them when the undo-log is trimmed, then you need
to use a weak reference. We don't currently have plain "weak
references" in ELisp, but we do have hash-tables whose keys and/or
values can be weak references (that's what I used in
`undo-equiv-table`).
Stefan
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Garbage collect and buffer-undo-list
2021-03-13 19:01 ` Stefan Monnier
@ 2021-03-13 19:16 ` Yuan Fu
0 siblings, 0 replies; 3+ messages in thread
From: Yuan Fu @ 2021-03-13 19:16 UTC (permalink / raw)
To: Stefan Monnier; +Cc: emacs-devel
> On Mar 13, 2021, at 2:01 PM, Stefan Monnier <monnier@iro.umontreal.ca> wrote:
>
>> I know the garbage collector trims buffer-undo-list. Does it collect the
>> cons cell if there are other references to that object (other than
>> buffer-undo-list)?
>
> No, it can't.
>
> If you want to keep a reference to some of those cons-cells but still
> want the GC to collect them when the undo-log is trimmed, then you need
> to use a weak reference. We don't currently have plain "weak
> references" in ELisp, but we do have hash-tables whose keys and/or
> values can be weak references (that's what I used in
> `undo-equiv-table`).
>
That’s cool, I do want the referenced object to survive. Thanks!
Yuan
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-03-13 18:17 Garbage collect and buffer-undo-list Yuan Fu
2021-03-13 19:01 ` Stefan Monnier
2021-03-13 19:16 ` Yuan Fu
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