[sheepdog] [PATCH 0/8] improve reference counting of data structures

[Liu Yuan]

On Tue, Jul 09, 2013 at 11:36:34AM +0900, Hitoshi Mitake wrote:
> Current sheep uses raw int and uatomic_{inc,dec} for reference
> counting of data structures. This is not a good practice because:
> 1. We can simply increment or decrement with ++ or -- operators of C
>    because these counters has a type of int. It causes typical
>    multithreading programming errors.
> 2. In sheep, only main thread is allowed to operate reference counts
>    of some data structures (e.g. client_info and request). But in
>    current sheep, reference counters for these structs also employ
>    uatomic_{inc,dec}. This is not necessary and confusing.
> 
> This patch implements two new data structures for reference counting:
> refcnt_t and main_refcnt_t. refcnt_t can be used for structs which can
> be get or put by multiple threads. main_refcnt_t can be used for
> structs which can be used by the main thread. These types leverage
> compiler support for detecting bad operations and manipulated safely
> than previous reference counters whose types are raw integer.
> 

There xxx_t wrapper makes things more complex and look unnecessary to me. I think 
uatomic_{inc, dec} is good enough to understand. And if you think some refcount
used in main thread only, we can simply unfold them into plain ++/--, rather
than introducing more construct.

Thanks
Yuan