Re: [RFC/PATCH 1/2] config: Add cache for config value querying

[Tanay Abhra <tanayabh@gmail.com>]

Hi,

On 05/26/2014 01:02 PM, Torsten Bögershausen wrote:
>> Add an internal cache with the all variable value pairs read from the usual
> "cache": The word "cache" is in Git often used for "index" 
Okay, point noted. I thought about choosing between "hashmap" and "cache" and chose
the later.
> "variable value" can be written as "key value"

I  had used the term "variable" to be consistent with the documentation
(api-config.txt). But I think "key" is much clearer.

> "usual": I don't think we handle "unusual" config files,
> (so can we drop the word usual ?)

Okay, noted.

> I think the (important) first line can be written like this:
> 
>> Add a hash table with the all key-value pairs read from the
> or
>> Add a hash table to cache all key-value pairs read from the
> 
>> config files(repo specific .git/config, user wide ~/.gitconfig and the global
>> /etc/gitconfig). Also, add two external functions `git_config_get_string` and
> Can we drop "Also" ?
>> @@ -37,6 +39,102 @@ static struct config_source *cf;
>>  
>>  static int zlib_compression_seen;
>>  
>> +struct hashmap config_cache;
>> +
>> +struct config_cache_node {
>> +	struct hashmap_entry ent;
>> +	struct strbuf key;
> Do we need a whole strbuf for the key?
> Or could a "char *key" work as well? 
> (and/or could it be "const char *key" ?

To maintain consistency with config.c. config.c uses strbuf for both key and value
throughout. I found the reason by git-blaming config.c. Key length is flexible so it
would be better to use a api construct such as strbuf for it.

>> +	struct string_list *value_list ;
> 
> 
> 
>> +static struct string_list *config_cache_get_value(const char *key)
>> +{
>> +	struct config_cache_node *e = config_cache_find_entry(key);
> why "e" ? Will "node" be easier to read ? Or entry ? 

Noted. Entry is much better.

>> +static void config_cache_set_value(const char *key, const char *value)
>> +{
>> +	struct config_cache_node *e;
>> +
>> +	if (!value)
>> +		return;
> Hm, either NULL could mean "unset==remove" the value, (but we don't do that, do we?
> 
> Or it could mean a programming or runtime error?, Should there be a warning ?

Nope. It is just a check to not save blank values for a key in the hashmap. Removal
functionality will come later. NULL==remove is implemented in
git_config_set_multivar_in_file(). We are not reading key value pairs from that, just
from git_config().
>> +
>> +	e = config_cache_find_entry(key);
>> +	if (!e) {
>> +		e = malloc(sizeof(*e));
>> +		hashmap_entry_init(e, strihash(key));
>> +		strbuf_init(&(e->key), 1024);
>> +		strbuf_addstr(&(e->key),key);
>> +		e->value_list = malloc(sizeof(struct string_list));
>> +		e->value_list->strdup_strings = 1;
>> +		e->value_list->nr = 0;
>> +		e->value_list->alloc = 0;
>> +		e->value_list->items = NULL;
>> +		e->value_list->cmp = NULL;
> When malloc() is replaced by xcalloc()  the x = NULL and y = 0 can go away,
> and the code is shorter and easier to read.

Much better, thanks.

>> +extern const char *git_config_get_string(const char *name)
>> +{
>> +	struct string_list *values;
>> +	int num_values;
>> +	char *result;
>> +	values = config_cache_get_value(name);
>> +	if (!values)
>> +		return NULL;
>> +	num_values = values->nr;
>> +	result = values->items[num_values-1].string ;
> We could get rid of the variable  "int num_values" by simply writing
> result = values->items[values->nr-1].string;
> 

Noted.


Cheers,
Tanay Abhra.