Date: Tue, 25 Feb 2025 21:44:32 -0300
On Tuesday, 25 February 2025 16:41:51 Brasilia Standard Time JOHN MORRISON via
Std-Proposals wrote:
> The memory footprint is almost as much as shared_ptr – shared_ptr requires a
> strong count on the control block whereas ptr_to_unique just needs a valid
> flag. Where ptr_to_unique is less burdensome is that it uses no thread
> safety mechanisms.
A control block with an refcounter (atomic or not) and a boolean flag has the
size of 8 bytes. You're going to need a pointer too, to the original pointer
value, bringing this up to 16 bytes. Your boolean flag and a strong reference
counter of only 0 or 1 are indistinguishable.
The only difference is that this does not need to store a deleter, because the
observers can't assume ownership and therefore don't need to worry about
destruction.
Std-Proposals wrote:
> The memory footprint is almost as much as shared_ptr – shared_ptr requires a
> strong count on the control block whereas ptr_to_unique just needs a valid
> flag. Where ptr_to_unique is less burdensome is that it uses no thread
> safety mechanisms.
A control block with an refcounter (atomic or not) and a boolean flag has the
size of 8 bytes. You're going to need a pointer too, to the original pointer
value, bringing this up to 16 bytes. Your boolean flag and a strong reference
counter of only 0 or 1 are indistinguishable.
The only difference is that this does not need to store a deleter, because the
observers can't assume ownership and therefore don't need to worry about
destruction.
-- Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org Principal Engineer - Intel DCAI Platform & System Engineering
Received on 2025-02-26 00:44:35