P1644R0 Add wait/notify to atomic<shared_ptr<T>>

Author: jensmaurer

source/utilities.tex

@@ -11737,6 +11737,10 @@
     bool compare_exchange_strong(shared_ptr<T>& expected, shared_ptr<T> desired,
                                  memory_order order = memory_order::seq_cst) noexcept;
 
+    void wait(shared_ptr<T> old, memory_order order = memory_order::seq_cst) const noexcept;
+    void notify_one() noexcept;
+    void notify_all() noexcept;
+
     constexpr atomic() noexcept = default;
     atomic(shared_ptr<T> desired) noexcept;
     atomic(const atomic&) = delete;
@@ -11951,6 +11955,70 @@
 shall be replaced by the value \tcode{memory_order::relaxed}.
 \end{itemdescr}
 
+\indexlibrarymember{wait}{atomic<shared_ptr<T>>}%
+\begin{itemdecl}
+void wait(shared_ptr<T> old, memory_order order = memory_order::seq_cst) const noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\expects
+\tcode{order} is
+neither \tcode{memory_order::release} nor \tcode{memory_order::acq_rel}.
+
+\pnum
+\effects
+Repeatedly performs the following steps, in order:
+\begin{itemize}
+\item
+  Evaluates \tcode{load(order)} and compares it to \tcode{old}.
+\item
+  If the two are not equivalent, returns.
+\item
+  Blocks until it
+  is unblocked by an atomic notifying operation or is unblocked spuriously.
+\end{itemize}
+
+\pnum
+\remarks
+Two \tcode{shared_ptr} objects are equivalent
+if they store the same pointer and either share ownership or are both empty.
+This function is an atomic waiting operation\iref{atomics.wait}.
+\end{itemdescr}
+
+\indexlibrarymember{notify_one}{atomic<shared_ptr<T>>}%
+\begin{itemdecl}
+void notify_one() noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Unblocks the execution of at least one atomic waiting operation
+that is eligible to be unblocked\iref{atomics.wait} by this call,
+if any such atomic waiting operations exist.
+
+\pnum
+\remarks
+This function is an atomic notifying operation\iref{atomics.wait}.
+\end{itemdescr}
+
+\indexlibrarymember{notify_all}{atomic<shared_ptr<T>>}%
+\begin{itemdecl}
+void notify_all() noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Unblocks the execution of all atomic waiting operations
+that are eligible to be unblocked\iref{atomics.wait} by this call.
+
+\pnum
+\remarks
+This function is an atomic notifying operation\iref{atomics.wait}.
+\end{itemdescr}
+
 \rSec3[util.smartptr.atomic.weak]{Atomic specialization for \tcode{weak_ptr}}
 \indexlibrary{\idxcode{atomic<weak_ptr<T>>}}%
 \begin{codeblock}
@@ -11977,6 +12045,10 @@
     bool compare_exchange_strong(weak_ptr<T>& expected, weak_ptr<T> desired,
                                  memory_order order = memory_order::seq_cst) noexcept;
 
+    void wait(weak_ptr<T> old, memory_order order = memory_order::seq_cst) const noexcept;
+    void notify_one() noexcept;
+    void notify_all() noexcept;
+
     constexpr atomic() noexcept = default;
     atomic(weak_ptr<T> desired) noexcept;
     atomic(const atomic&) = delete;
@@ -12189,6 +12261,71 @@
 a value of \tcode{memory_order::release}
 shall be replaced by the value \tcode{memory_order::relaxed}.
 \end{itemdescr}
+
+\indexlibrarymember{wait}{atomic<weak_ptr<T>>}%
+\begin{itemdecl}
+void wait(weak_ptr<T> old, memory_order order = memory_order::seq_cst) const noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\expects
+\tcode{order} is
+neither \tcode{memory_order::release} nor \tcode{memory_order::acq_rel}.
+
+\pnum
+\effects
+Repeatedly performs the following steps, in order:
+\begin{itemize}
+\item
+  Evaluates \tcode{load(order)} and compares it to \tcode{old}.
+\item
+  If the two are not equivalent, returns.
+\item
+  Blocks until it
+  is unblocked by an atomic notifying operation or is unblocked spuriously.
+\end{itemize}
+
+\pnum
+\remarks
+Two \tcode{weak_ptr} objects are equivalent
+if they store the same pointer and either share ownership or are both empty.
+This function is an atomic waiting operation\iref{atomics.wait}.
+\end{itemdescr}
+
+
+\indexlibrarymember{notify_one}{atomic<weak_ptr<T>>}%
+\begin{itemdecl}
+void notify_one() noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Unblocks the execution of at least one atomic waiting operation
+that is eligible to be unblocked\iref{atomics.wait} by this call,
+if any such atomic waiting operations exist.
+
+\pnum
+\remarks
+This function is an atomic notifying operation\iref{atomics.wait}.
+\end{itemdescr}
+
+\indexlibrarymember{notify_all}{atomic<weak_ptr<T>>}%
+\begin{itemdecl}
+void notify_all() noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Unblocks the execution of all atomic waiting operations
+that are eligible to be unblocked\iref{atomics.wait} by this call.
+
+\pnum
+\remarks
+This function is an atomic notifying operation\iref{atomics.wait}.
+\end{itemdescr}
 \indextext{atomic smart pointers|)}
 
 \rSec1[mem.res]{Memory resources}