P2869R4 Remove deprecated atomic free function API for shared_ptr

The Annex C wording is modeled on the compatibility with C form,
and should be revised without the "difficulty of converting"
clause, probably with a simple code example in "Effects".

Author: AlisdairM

source/compatibility.tex

@@ -155,6 +155,23 @@
                                                                         // OK in \CppXXVI{}
 \end{codeblock}
 
+\nodiffref
+\change
+Removal of atomic access API for \tcode{shared_ptr} objects.
+\rationale
+The old behavior was brittle. \tcode{shared_ptr} objects using the old API were
+not protected by the type system, and certain interactions with code not using
+this API would, in some cases, silently produce undefined behavior. A complete
+type-safe replacement is provided in the form of \tcode{atomic<shared_ptr<T>>}.
+\effect
+Deletion of an old feature where a superior replacement exists within the
+standard.
+\difficulty
+Violations will be diagnosed by the \Cpp{} translator, as there are no
+remaining overloads that would match such calls. Violations are addressed by
+replacing affected \tcode{shared_ptr<T>} objects with
+\tcode{atomic<shared_ptr<T>>}.
+
 \nodiffref
 \change
 Remove the \tcode{basic_string::reserve()} overload with no parameters.

source/future.tex

@@ -675,274 +675,6 @@
 \tcode{current}.
 \end{itemdescr}
 
-\rSec1[depr.util.smartptr.shared.atomic]{Deprecated \tcode{shared_ptr} atomic access}
-
-\pnum
-The header \libheaderref{memory} has the following additions:
-
-\indexlibraryglobal{shared_ptr}%
-\begin{codeblock}
-namespace std {
-  template<class T>
-    bool atomic_is_lock_free(const shared_ptr<T>* p);
-
-  template<class T>
-    shared_ptr<T> atomic_load(const shared_ptr<T>* p);
-  template<class T>
-    shared_ptr<T> atomic_load_explicit(const shared_ptr<T>* p, memory_order mo);
-
-  template<class T>
-    void atomic_store(shared_ptr<T>* p, shared_ptr<T> r);
-  template<class T>
-    void atomic_store_explicit(shared_ptr<T>* p, shared_ptr<T> r, memory_order mo);
-
-  template<class T>
-    shared_ptr<T> atomic_exchange(shared_ptr<T>* p, shared_ptr<T> r);
-  template<class T>
-    shared_ptr<T> atomic_exchange_explicit(shared_ptr<T>* p, shared_ptr<T> r, memory_order mo);
-
-  template<class T>
-    bool atomic_compare_exchange_weak(shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w);
-  template<class T>
-    bool atomic_compare_exchange_strong(shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w);
-  template<class T>
-    bool atomic_compare_exchange_weak_explicit(
-      shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w,
-      memory_order success, memory_order failure);
-  template<class T>
-    bool atomic_compare_exchange_strong_explicit(
-      shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w,
-      memory_order success, memory_order failure);
-}
-\end{codeblock}
-
-\pnum
-Concurrent access to a \tcode{shared_ptr} object from multiple threads does not
-introduce a data race if the access is done exclusively via the functions in
-this subclause and the instance is passed as their first argument.
-
-\pnum
-The meaning of the arguments of type \tcode{memory_order} is explained in~\ref{atomics.order}.
-
-\indexlibrarymember{atomic_is_lock_free}{shared_ptr}%
-\begin{itemdecl}
-template<class T> bool atomic_is_lock_free(const shared_ptr<T>* p);
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\expects
-\tcode{p} is not null.
-
-\pnum
-\returns
-\tcode{true} if atomic access to \tcode{*p} is lock-free, \tcode{false} otherwise.
-
-\pnum
-\throws
-Nothing.
-\end{itemdescr}
-
-\indexlibrarymember{atomic_load}{shared_ptr}%
-\begin{itemdecl}
-template<class T> shared_ptr<T> atomic_load(const shared_ptr<T>* p);
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\expects
-\tcode{p} is not null.
-
-\pnum
-\returns
-\tcode{atomic_load_explicit(p, memory_order::seq_cst)}.
-
-\pnum
-\throws
-Nothing.
-\end{itemdescr}
-
-\indexlibrarymember{atomic_load_explicit}{shared_ptr}%
-\begin{itemdecl}
-template<class T> shared_ptr<T> atomic_load_explicit(const shared_ptr<T>* p, memory_order mo);
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\expects
-\tcode{p} is not null.
-\tcode{mo} is neither \tcode{memory_order::release} nor \tcode{memory_order::acq_rel}.
-
-\pnum
-\returns
-\tcode{*p}.
-
-\pnum
-\throws
-Nothing.
-\end{itemdescr}
-
-\indexlibrarymember{atomic_store}{shared_ptr}%
-\begin{itemdecl}
-template<class T> void atomic_store(shared_ptr<T>* p, shared_ptr<T> r);
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\expects
-\tcode{p} is not null.
-
-\pnum
-\effects
-As if by \tcode{atomic_store_explicit(p, r, memory_order::seq_cst)}.
-
-\pnum
-\throws
-Nothing.
-\end{itemdescr}
-
-\indexlibrarymember{atomic_store_explicit}{shared_ptr}%
-\begin{itemdecl}
-template<class T> void atomic_store_explicit(shared_ptr<T>* p, shared_ptr<T> r, memory_order mo);
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\expects
-\tcode{p} is not null.
-\tcode{mo} is neither \tcode{memory_order::acquire} nor \tcode{memory_order::acq_rel}.
-
-\pnum
-\effects
-As if by \tcode{p->swap(r)}.
-
-\pnum
-\throws
-Nothing.
-\end{itemdescr}
-
-\indexlibrarymember{atomic_exchange}{shared_ptr}%
-\begin{itemdecl}
-template<class T> shared_ptr<T> atomic_exchange(shared_ptr<T>* p, shared_ptr<T> r);
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\expects
-\tcode{p} is not null.
-
-\pnum
-\returns
-\tcode{atomic_exchange_explicit(p, r, memory_order::seq_cst)}.
-
-\pnum
-\throws
-Nothing.
-\end{itemdescr}
-
-\indexlibrarymember{atomic_exchange_explicit}{shared_ptr}%
-\begin{itemdecl}
-template<class T>
-  shared_ptr<T> atomic_exchange_explicit(shared_ptr<T>* p, shared_ptr<T> r, memory_order mo);
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\expects
-\tcode{p} is not null.
-
-\pnum
-\effects
-As if by \tcode{p->swap(r)}.
-
-\pnum
-\returns
-The previous value of \tcode{*p}.
-
-\pnum
-\throws
-Nothing.
-\end{itemdescr}
-
-\indexlibrarymember{atomic_compare_exchange_weak}{shared_ptr}%
-\begin{itemdecl}
-template<class T>
-  bool atomic_compare_exchange_weak(shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w);
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\expects
-\tcode{p} is not null and \tcode{v} is not null.
-
-\pnum
-\returns
-\begin{codeblock}
-atomic_compare_exchange_weak_explicit(p, v, w, memory_order::seq_cst, memory_order::seq_cst)
-\end{codeblock}
-
-\pnum
-\throws
-Nothing.
-\end{itemdescr}
-
-\indexlibrarymember{atomic_compare_exchange_strong}{shared_ptr}%
-\begin{itemdecl}
-template<class T>
-  bool atomic_compare_exchange_strong(shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w);
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\returns
-\begin{codeblock}
-atomic_compare_exchange_strong_explicit(p, v, w, memory_order::seq_cst,
-                                        memory_order::seq_cst)
-\end{codeblock}
-\end{itemdescr}
-
-\indexlibrarymember{atomic_compare_exchange_weak_explicit}{shared_ptr}%
-\indexlibrarymember{atomic_compare_exchange_strong_explicit}{shared_ptr}%
-\begin{itemdecl}
-template<class T>
-  bool atomic_compare_exchange_weak_explicit(
-    shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w,
-    memory_order success, memory_order failure);
-template<class T>
-  bool atomic_compare_exchange_strong_explicit(
-    shared_ptr<T>* p, shared_ptr<T>* v, shared_ptr<T> w,
-    memory_order success, memory_order failure);
-\end{itemdecl}
-
-\begin{itemdescr}
-\pnum
-\expects
-\tcode{p} is not null and \tcode{v} is not null.
-The \tcode{failure} argument is neither \tcode{memory_order::release} nor
-\tcode{memory_order::acq_rel}.
-
-\pnum
-\effects
-If \tcode{*p} is equivalent to \tcode{*v}, assigns \tcode{w} to
-\tcode{*p} and has synchronization semantics corresponding to the value of
-\tcode{success}, otherwise assigns \tcode{*p} to \tcode{*v} and has
-synchronization semantics corresponding to the value of \tcode{failure}.
-
-\pnum
-\returns
-\tcode{true} if \tcode{*p} was equivalent to \tcode{*v}, \tcode{false} otherwise.
-
-\pnum
-\throws
-Nothing.
-
-\pnum
-\remarks
-Two \tcode{shared_ptr} objects are equivalent if they store the same
-pointer value and share ownership.
-The weak form may fail spuriously. See~\ref{atomics.types.operations}.
-\end{itemdescr}
-
 \rSec1[depr.format]{Deprecated formatting}
 
 \rSec2[depr.format.syn]{Header \tcode{<format>} synopsis}

source/xrefdelta.tex

@@ -59,6 +59,9 @@
 \removedxref{depr.strstreambuf.members}
 \removedxref{depr.strstreambuf.virtuals}
 
+% P2869R4 Mandating Annex D
+\removedxref{depr.util.smartptr.shared.atomic}
+
 %%% Renamed sections.
 %%% Examples:
 %