Fw: [patch] Make std::tr1::shared_ptr thread-safe.

[Alexander Terekhov]

Just to clarify. Peter Dimov wrote:

: Apologies for repeating myself, but this is an important point: the empty 
: critical sections fix a different problem (memory visibility). The 
: compare_and_swap way is not a substitute for them. It eliminates the 
: non-empty critical section in add_ref_lock, nothing more. 

Right. As for memory visibility, the issue here is that shared_ptr's 
"control block" is mutable object. The msync protocol on "self count" 
must take care of inter-thread ordering with respect to modifications 
(of another "use count", I mean) and destruction of control block. 
If it doesn't, then empty critical sections at the right places (on 
the same lock) can be used to sorta compensate that.

regards,
alexander.