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Re: About shared substrings
From: |
Mikael Djurfeldt |
Subject: |
Re: About shared substrings |
Date: |
Fri, 16 Jan 2004 16:54:51 -0500 |
User-agent: |
Gnus/5.1006 (Gnus v5.10.6) Emacs/21.3 (gnu/linux) |
Roland Orre <address@hidden> writes:
> I discussed this issue with Mikael Djurfeldt today and then he came up
> with the following solution:
>
> SCM substring_table;
>
> SCM scm_make_shared_substring (SCM parent, SCM start, SCM end)
> {
> SCM substring;
> char *mem;
> int c_start, c_end;
> SCM_VALIDATE_SUBSTRING_SPEC_COPY (1, parent, mem,
> 2, start, c_start,
> 3, end, c_end);
> substring = scm_cell (SCM_MAKE_STRING_TAG (c_end - c_start),
> (scm_t_bits) (mem + c_start));
> scm_hash_set_x (substring_table, substring, parent);
> return substring;
> }
>
> where the following is put in the main:
> substring_table
> = scm_permanent_object (scm_make_weak_key_hash_table (SCM_UNDEFINED));
>
> This is almost magical :)
Unfortunately, it *is* magical. In addition, it is necessary to hand
the newly created substring to a guardian. If we then add a hook
function to some suitable GC hook which loops through all unreferenced
substrings and sets their address pointer to NULL, everything should
work.
If we *don't* do that, the same area of memory will be freed
repeatedly, which is not optimal.
> Mikael Djurfeldt is relly the most clever programmer I know.
Many thanks for the kind words! Yes, I am usually a blazing genius.
My mistake above must certainly be due to something in my coffee or
so... :)
M
- Re: shared-substrings missing in 1.7, (continued)