https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118854
--- Comment #13 from Nicholas Williams <nicholas at nicholaswilliams dot net>
---
(In reply to Jonathan Wakely from comment #10)
> If you need to make copies of a shared_ptr while also modifying it, you need
> to use std::atomic<std::shared_ptr<T>> (or
> std::experimental::atomic_shared_ptr).
Using std::atomic<std::shared_ptr> results in the same race condition
heap-use-after-free while copying the shared_ptr:
...
#0 0x40a582 in __gnu_cxx::__atomic_add(int volatile*, int)
/opt/rh/gcc-toolset-14/root/usr/include/c++/14/ext/atomicity.h:71
#1 0x40a582 in __gnu_cxx::__atomic_add_dispatch(int*, int)
/opt/rh/gcc-toolset-14/root/usr/include/c++/14/ext/atomicity.h:111
#2 0x40a582 in
std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_add_ref_copy()
/opt/rh/gcc-toolset-14/root/usr/include/c++/14/bits/shared_ptr_base.h:152
#3 0x409cd6 in std::_Sp_atomic<std::shared_ptr<Resource>
>::_S_add_ref(std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>*)
/opt/rh/gcc-toolset-14/root/usr/include/c++/14/bits/shared_ptr_atomic.h:536
#4 0x4090d3 in std::_Sp_atomic<std::shared_ptr<Resource>
>::load(std::memory_order) const
/opt/rh/gcc-toolset-14/root/usr/include/c++/14/bits/shared_ptr_atomic.h:568
#5 0x407874 in std::atomic<std::shared_ptr<Resource>
>::load(std::memory_order) const
/opt/rh/gcc-toolset-14/root/usr/include/c++/14/bits/shared_ptr_atomic.h:656
...
(In reply to Jonathan Wakely from comment #12)
> ***any of those accesses uses a non-const member function of shared_ptr then
> a data race will occur***
shared_ptr::shared_ptr( shared_ptr const & other );
By definition, uses of `other` should exclusively use only const members, not
non-const members, of `other`, because `other` is declared `const`.
