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

[Tanay Abhra <tanayabh@gmail.com>]

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(+)

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1.9.0.GIT