[patch] Add a level of abstraction to condvars and mutexes so we can initalize them late

[Havoc Pennington]

John (J5) Palmieri wrote:
> *location_p == NULL indicates OOM (as it does with _dbus_mutex_new).  I
> can change this to returning a bool but isn't that superfluous or is the
> goal here to make it clearer to a developer? 
> 

Ah OK, that sounds fine, obvious in retrospect.

>> The test thread_init_generation == 0 should be
>> thread_init_generation != _dbus_current_generation instead, so multiple 
>> generations can be used.
> 
> Easy change but I don't understand what a generation is and how threads
> can be initialized more than once.  Just for my knowledge can you give a
> brief explanation.
> 

dbus can be shut down (completely uninitialized) with dbus_shutdown(), 
at that point the generation is incremented and any of the init/setup 
stuff can be used again.

Times when you might shut down:
  - to help in memory leak tracking (e.g. the test suite relies on it)
  - if you are using the library from a plugin and know the main app
    isn't using it

The generation counter is used rather than a simple "bool initialized" 
because it lets us detect more kinds of mistake, such as using a 
connection after shutting down the generation that created it.

Havoc