Re: [PATCH] find_pack_entry(): do not keep packed_git pointer locally

[Nguyen Thai Ngoc Duy <pclouds@gmail.com>]

(Pulling Nico in for Q2 below. No snipping so he has a context)

2012/1/31 Junio C Hamano <gitster@pobox.com>:
> Nguyễn Thái Ngọc Duy  <pclouds@gmail.com> writes:
>
>> Commit f7c22cc (always start looking up objects in the last used pack
>> first - 2007-05-30) introduces a static packed_git* pointer as an
>> optimization.  The kept pointer however may become invalid if
>> free_pack_by_name() happens to free that particular pack.
>>
>> Current code base does not access packs after calling
>> free_pack_by_name() so it should not be a problem. Anyway, move the
>> pointer out so that free_pack_by_name() can reset it to avoid running
>> into troubles in future.
>>
>> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
>> ---
>
> Thanks. Two curiosities:
>
> - Why is there no hunk to actually clear the pointer in
>  free_pack_by_name() in this patch?

I think it's there (the patch did work for me when I tried to
integrate repack to pack-objects).

-- 8<--
> @@ -720,6 +722,8 @@ void free_pack_by_name(const char *pack_name)
>                       close_pack_index(p);
>                       free(p->bad_object_sha1);
>                       *pp = p->next;
> +                     if (find_pack_entry_last_found == p)
> +                             find_pack_entry_last_found = (void*)1;
>                       free(p);
>                       return;
>               }
-- 8< --

>  - Could we make the magic (void *)1 value a #define'd constant? Perhaps
>   we could even use NULL for that purpose?

Q1. Sure.

Q2. No NULL is probably not suitable. I think Nico wanted to express
"we tried to find but found none (i.e. NULL)" too and 1 means "no we
have not tried".

>> diff --git a/sha1_file.c b/sha1_file.c
>> index 88f2151..4ecc953 100644
>> --- a/sha1_file.c
>> +++ b/sha1_file.c
>> @@ -54,6 +54,8 @@ static struct cached_object empty_tree = {
>>       0
>>  };
>>
>> +static struct packed_git *find_pack_entry_last_found = (void *)1;
>> +
>>  static struct cached_object *find_cached_object(const unsigned char *sha1)
>>  {
>>       int i;
>> @@ -720,6 +722,8 @@ void free_pack_by_name(const char *pack_name)
>>                       close_pack_index(p);
>>                       free(p->bad_object_sha1);
>>                       *pp = p->next;
>> +                     if (find_pack_entry_last_found == p)
>> +                             find_pack_entry_last_found = (void*)1;
>>                       free(p);
>>                       return;
>>               }
>> @@ -2012,14 +2016,13 @@ int is_pack_valid(struct packed_git *p)
>>
>>  static int find_pack_entry(const unsigned char *sha1, struct pack_entry *e)
>>  {
>> -     static struct packed_git *last_found = (void *)1;
>>       struct packed_git *p;
>>       off_t offset;
>>
>>       prepare_packed_git();
>>       if (!packed_git)
>>               return 0;
>> -     p = (last_found == (void *)1) ? packed_git : last_found;
>> +     p = (find_pack_entry_last_found == (void *)1) ? packed_git : find_pack_entry_last_found;
>>
>>       do {
>>               if (p->num_bad_objects) {
>> @@ -2046,16 +2049,16 @@ static int find_pack_entry(const unsigned char *sha1, struct pack_entry *e)
>>                       e->offset = offset;
>>                       e->p = p;
>>                       hashcpy(e->sha1, sha1);
>> -                     last_found = p;
>> +                     find_pack_entry_last_found = p;
>>                       return 1;
>>               }
>>
>>               next:
>> -             if (p == last_found)
>> +             if (p == find_pack_entry_last_found)
>>                       p = packed_git;
>>               else
>>                       p = p->next;
>> -             if (p == last_found)
>> +             if (p == find_pack_entry_last_found)
>>                       p = p->next;
>>       } while (p);
>>       return 0;



-- 
Duy