Re: [SmartPtr] intrusive_ref_counter CounterPolicyT requirements API?

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2020-12-04 19:04:26

On 12/4/20 8:44 PM, Peter Dimov via Boost wrote:
> Andrey Semashev wrote:
> 
>> > [*] Incidentally we want to increment with memory order relaxed 
>> instead > of acq_rel.
>>
>> This would probably be a good optimization in atomic_count.
> 
> atomic_count can't do this because it doesn't have enough knowledge 
> about the context in which it's used.
> 
> https://github.com/boostorg/smart_ptr/blob/678a544d27d016204c6aed6403b1ffdf0b021d1b/include/boost/smart_ptr/detail/atomic_count.hpp#L33-L43 
> 
> 
> In principle you can use negative values for the count, again destroying 
> on zero.
> 
> I could have specified ++a to be relaxed, but it is what it is at this 
> point.

atomic_count is formally an implementation detail of Boost.SmartPtr, so 
you can define it as you see fit. If it is only used as a reference 
counter, you could make it increment with relaxed semantics. Or add a 
separate member with such behavior (but then the operator++ would become 
unused).