Subject: Re: [PATCH v3 2/3] config: add hashtable for config parsing & retrieval

From: Ramsay Jones <[email-masked]>
Date: Tue, 24 Jun 2014 16:32:56 +0100

On 23/06/14 17:20, Tanay Abhra wrote:
> On 06/23/2014 07:57 AM, Ramsay Jones wrote:
>> On 23/06/14 11:11, Tanay Abhra wrote:
[snip]

>>> +static struct hashmap *get_config_cache(void)
>>> +{
>>> +	static struct hashmap config_cache;
>>> +	if (!hashmap_initialized) {
>>> +		config_cache_init(&config_cache);
>>> +		hashmap_initialized = 1;
>>> +		git_config(config_cache_callback, NULL);
>>> +	}
>>> +	return &config_cache;
>>> +}
>>
>> [I have not been following this series at all (sorry I haven't had
>> the time to spare), so take these comments with a very big pinch of
>> salt! ie just ignore me if it's already been discussed etc. ;-) ]
>>
>> The 'git config' command can be used to read arbitrary files (so long
>> as they conform to the config syntax). For example, see the --file and
>> --blob options to git-config. At present, I think only scripted commands
>> use this facility (eg git-submodule). Noting the singleton config_cache,
>> what happens when git-submodule becomes a C builtin, or indeed any other
>> C builtin wants to take advantage of the new code when processing a non-
>> standard config file?
>>
> 
> This series was mainly to replace git_config() invocations around the codebase.
> There are currently 111 git_config() invocations, each of which causes a file
> reread whenever called. git_config() only feeds values from the standard config
> files(i.e repo, user and global config).
> 
> For reading config values from specific files or blobs, there are three functions
> git_config_with_options, git_config_from_file & git_config_from_blob which can be
> easily used inside a C builtin or anywhere in the code.
> 
> The bulk of git_config_api calls are only for git_config(). For example,
> git_config_from_file() has three hits only in entire codebase,
> git_config_with_options() has 5 hits, so I concentrated on generating a cache
> for the usual config files only. For other files, the callers can fall back on older
> API functions like I had mentioned above.
> 
> Forgive me if I inferred your question incorrectly. More below.

Hmm, maybe. The "... take advantage of the new code" refers to the
possibility (or otherwise) of re-using your work to update these
"older API" functions to the new API style. (also, see Junio's response).
[In order to do this, I would have expected to see one hash table
for each file/blob, so the singleton object took me by surprise.]

An "out of scope for this project" is a perfectly acceptable
response (*particularly* since it is very late in the day to be
bringing this up!).

>>> +static struct config_cache_entry *config_cache_find_entry(const char *key)
>>> +{
>>> +	struct hashmap *config_cache;
>>> +	struct config_cache_entry k;
>>> +	struct config_cache_entry *found_entry;
>>> +	char *normalized_key;
>>> +	int ret;
>>> +	config_cache = get_config_cache();
>>> +	ret = git_config_parse_key(key, &normalized_key, NULL);
>>> +
>>> +	if (ret)
>>> +		return NULL;
>>> +
>>> +	hashmap_entry_init(&k, strhash(normalized_key));
>>> +	k.key = normalized_key;
>>> +	found_entry = hashmap_get(config_cache, &k, NULL);
>>> +	free(normalized_key);
>>> +	return found_entry;
>>> +}
>>> +
>>> +static struct string_list *config_cache_get_value(const char *key)
>>> +{
>>> +	struct config_cache_entry *e = config_cache_find_entry(key);
>>> +	return e ? &e->value_list : NULL;
>>> +}
>>> +
>>> +static int config_cache_add_value(const char *key, const char *value)
>>> +{
>>> +	struct hashmap *config_cache;
>>> +	struct config_cache_entry *e;
>>> +	struct string_list_item *item;
>>> +	int *boolean_null_flag;
>>> +
>>> +	config_cache = get_config_cache();
>>> +	e = config_cache_find_entry(key);
>>> +
>>> +	boolean_null_flag = xcalloc(1, sizeof(*boolean_null_flag));
>>> +
>>> +	if (!e) {
>>> +		e = xmalloc(sizeof(*e));
>>> +		hashmap_entry_init(e, strhash(key));
>>> +		e->key = xstrdup(key);
>>
>> config_cache_find_entry() searches for (and hashes the) normalized_key.
>> Should you not be entering the normalized key here?
>>
> 
> config_cache_add_value() is fed key-values pairs through the git_config()
> callback mechanism, which normalises the key beforehand, so no need for
> renormalising.

Ah, yes, I forgot that the parsing code does a tolower() at various
places while accumulating the key string. So the (potentially) non-
normalized keys come from the user via the new API functions and,
rather than putting code to normalize the key in each of those,
just do it once in config_cache_find_entry(). (Although, you could
possibly do that in config_cache_get_value()).  OK.

Hmm, maybe add a short comment to that effect? dunno.

ATB,
Ramsay Jones