Why use shared_ptr in the first place? You already use the promise/future protocol as the thread safe communication channel between the producer and consumer. I would consider getting a shared_future from the future and copy instances of it for each threads that would want to get the value.

Julien V.

On December 11, 2023 5:23:23 p.m. EST, Andrey Semashev via Std-Proposals <std-proposals_at_[hidden]> wrote:
>On 12/11/23 22:42, Marcin Jaczewski via Std-Proposals wrote:
>> pon., 11 gru 2023 o 18:26 Thiago Macieira via Std-Proposals
>> <std-proposals_at_[hidden]> napisał(a):
>>>
>>> On Monday, 11 December 2023 08:45:31 PST Valentin Palade wrote:
>>>> Doing a local copy as Jonathan suggests, will make no difference, with
>>>> threads running concurrently, we can still have use_count() return anything
>>>> between 1 and 5.
>>>>
>>>> Or am I missing something?
>>>
>>> No. It can be between 1 and 5.
>>>
>>> But if it's 1, then you have the only copy and there is no other thread seeing
>>> this object. The number can't change unless the current thread changes it.
>>
>> But all threads can return 5 too. As check is done before decrement
>> every one can observe the state before it.
>> And this means no thread can get 1 and acquire the last instance.
>> We need to guarantee that one thread will be the least instance.
>
>Yes, but the same can happen with the proposed resurrect() method as well.
>
>If this is a concern then a better solution is to use a custom deleter
>that will pass the object to the producer instead of deleting it.
>
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