[RFC/PATCH 0/2] Git config cache & special querying api utilizing the cache

Hi,

This is my first patch series for this year's GSoC. My project is "Git Config API improvements". The link of my proposal is appended below [1].

The aim of this patch series is to generate a cache for querying values from the config files in a non callback manner as the current method reads and parses the config files every time a value is queried for.

The cache is generated from hooking the update_cache function to the current parsing and callback mechanism in config.c. It is implemented as an hashmap using the hashmap-api with variables and its corresponding values list as its members. The values in the list are sorted in order of increasing priority. The cache is initialised in git_config_early() as it is the first time a `git_config` function is called during program startup. setup_git_directory_gently() calls git_config_early() which in turn reads every config file (local, user and global config files).

get_value() in config.c feeds variable and values into the callback function. Using this function as a hook, we update the cache. Also, we add two new functions to the config-api git_config_get_string() and git_config_get_string_multi() for querying in a non callback manner from the cache.

I have run the tests and debug the code and it works, but I have to add a few things,

1. Invalidity check: if a config file is written into, update the cache.
   I am using git_config_set_multivar_in_file() as an update hook.

2. Metadata about the variables and values. I have added only the file
   from each variable value pair comes in an upcoming series.

What else should I add or implement ;is my approach right? 

[1] https://drive.google.com/file/d/0B4suZ-aHqDcnSUZJRXVTTnZUN1E/edit?usp=sharing

Cheers, Tanay Abhra.

Tanay Abhra (2):
  config: Add cache for config value querying
  config: Add new query functions to the api

 Documentation/technical/api-config.txt |  19 ++++++
 cache.h                                |   2 +
 config.c                               | 105 +++++++++++++++++++++++++++++++++
 3 files changed, 126 insertions(+)