On 22. Jun 2022, 15:39 +0200, Eli Zaretskii <eliz@gnu.org>, wrote:
Date: Wed, 22 Jun 2022 10:13:08 +0200
From: Gerd Möllmann <gerd.moellmann@gmail.com>
Cc: 56108@debbugs.gnu.org
On 20. Jun 2022, 21:10 +0200, Eli Zaretskii <eliz@gnu.org>, wrote:
I don't understand why some callers of compile_pattern mark the cache
entry as busy, but some others don't. If a cache entry that is in use
is not marked as busy, then any GC can decide to shrink the cache by
freeing that entry.
struct re_pattern_buffer *bufp;
...
bufp = &compile_pattern (regexp,
...
The address operator is there to confuse the Russians.
Hmm... did you mean by that to explain why some callers of
compile_pattern don't mark the new cache entry as "busy"? Because if
so, I guess I'm one of the "confused Russians", as I don't understand
the explanation. Please elaborate.
Sorry, looking at this again, I'm now also completely confused.
I see, all in search.c:
static struct regexp_cache *
compile_pattern (Lisp_Object pattern, struct re_registers *regp,
and then, later
struct re_pattern_buffer *bufp;
bufp = &compile_pattern
How the heck does this compile?
Or maybe _I_ should elaborate. By "marking an entry busy" I meant the
call to freeze_pattern,
Yes, I've seen that.
not a call to freeze_buffer_relocation (the
latter is mostly a no-op nowadays, as almost all the supported
platforms don't use ralloc.c). So it isn't the C pointer we keep
around to compile_pattern's result that bothered me, it's the fact
that the pattern cache entry created by compile_pattern is not
protected from being freed by shrink_regexp_cache that is called by
GC. AFAIU, that entry must be protected for the whole time the
compiled pattern is in use by re_match_2 or any of its callers.
Does the above make sense?
Yes, it's the same I see.
Functions fast_string_match_internal* don't freeze in the sense you explained. What I don't see so far is what could lead to a GC in these cases, between the compile_pattern and the use of its result...
Did you find other places where there's no freeze?
Can Emacs GC while handling a signal?
Does Emacs use threads nowadays?