[Bug libstdc++/86189] not equal allocators not behaving as expected
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86189 --- Comment #5 from Jonathan Wakely --- [allocator.requirements]
[Bug libstdc++/86189] not equal allocators not behaving as expected
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86189
--- Comment #4 from Rian Quinn ---
Nope, I think that is the root of the issue. Where exactly does the spec
state that as this is the first I have heard of this.
Thanks a ton,
- Rian
On Mon, Jun 18, 2018 at 6:31 AM, redi at gcc dot gnu.org <
gcc-bugzi...@gcc.gnu.org> wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86189
>
> Jonathan Wakely changed:
>
>What|Removed |Added
>
>
> Status|UNCONFIRMED |WAITING
>Last reconfirmed||2018-06-18
> Ever confirmed|0 |1
>
> --- Comment #1 from Jonathan Wakely ---
> (In reply to Rian Quinn from comment #0)
> > template
> > bool operator==(const myallocator4 &, const myallocator4 &)
> > { return false; }
> >
> > template
> > bool operator!=(const myallocator4 &, const myallocator4 &)
> > { return true; }
>
> Your allocators *always* compare unequal to all other instances of the same
> allocator. This is invalid, a copy-constructed allocator must compare
> equal to
> the original, and be able to deallocate its memory.
>
> I haven't analysed any further, but I assume that the containers are using
> a
> copy to deallocate, which is perfectly fine. If you think the problem lies
> elsewhere please reopen this.
>
> --
> You are receiving this mail because:
> You reported the bug.
[Bug libstdc++/86189] not equal allocators not behaving as expected
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86189 Jonathan Wakely changed: What|Removed |Added Status|WAITING |RESOLVED Resolution|--- |INVALID --- Comment #3 from Jonathan Wakely --- (In reply to Jonathan Wakely from comment #1) > Your allocators *always* compare unequal to all other instances of the same > allocator. This is invalid, a copy-constructed allocator must compare equal > to the original, and be able to deallocate its memory. See the rows defining equality comparison and copy construction at http://en.cppreference.com/w/cpp/named_req/Allocator#Requirements Allocator propagation rules do not mean that the same specific instance of the allocator must be used for all allocations and deallocation, only one that compares equal to the original one. With your allocator that's obviously impossible, because no allocators ever compare equal (even when you compare an allocator to itself!) Stateful allocators need to be a lightweight handle for some allocation resource managed elsewhere, and two allocators compare equal if they use the same resource. That means that you should never depend on the identity (i.e. address) of allocator objects, only on their equivalence (as determined by operator==). Having looked at your code further, the test is simply completely broken. When an allocator propagates on copy assignment the allocator gets assigned, so that the "value" of the new allocator replaces the "value" of the old allocator. That doesn't change the allocator's address. The object still has the same address, it just gets a new "value". But your allocators don't have any "value" they only care about their identity (i.e. address). This report is INVALID. (In reply to Jonathan Wakely from comment #2) > You know you can just not name a parameter, instead of casting it to void? Ah yes, I see you've done that elsewhere.
[Bug libstdc++/86189] not equal allocators not behaving as expected
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86189
--- Comment #2 from Jonathan Wakely ---
(In reply to Rian Quinn from comment #0)
> template
> myallocator4(const myallocator4 &other) noexcept
> { (void) other; }
You know you can just not name a parameter, instead of casting it to void?
template
myallocator4(const myallocator4 &) noexcept
{ }
[Bug libstdc++/86189] not equal allocators not behaving as expected
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86189
Jonathan Wakely changed:
What|Removed |Added
Status|UNCONFIRMED |WAITING
Last reconfirmed||2018-06-18
Ever confirmed|0 |1
--- Comment #1 from Jonathan Wakely ---
(In reply to Rian Quinn from comment #0)
> template
> bool operator==(const myallocator4 &, const myallocator4 &)
> { return false; }
>
> template
> bool operator!=(const myallocator4 &, const myallocator4 &)
> { return true; }
Your allocators *always* compare unequal to all other instances of the same
allocator. This is invalid, a copy-constructed allocator must compare equal to
the original, and be able to deallocate its memory.
I haven't analysed any further, but I assume that the containers are using a
copy to deallocate, which is perfectly fine. If you think the problem lies
elsewhere please reopen this.
