Merge 2019-11 LWG Motion 18

P1960R0 NB Comment Changes Reviewed by SG1

Author: zygoloid

source/atomics.tex

@@ -739,8 +739,8 @@
                                  memory_order = memory_order_seq_cst) const noexcept;
 
     void wait(T, memory_order = memory_order::seq_cst) const noexcept;
-    void notify_one() noexcept;
-    void notify_all() noexcept;
+    void notify_one() const noexcept;
+    void notify_all() const noexcept;
   };
 }
 \end{codeblock}
@@ -830,7 +830,8 @@
 \begin{itemdescr}
 \pnum
 \returns
-\tcode{true} if the object's operations are lock-free,
+\tcode{true} if operations on all objects of the type \tcode{atomic_ref<T>}
+are lock-free,
 \tcode{false} otherwise.
 \end{itemdescr}
 
@@ -1081,7 +1082,7 @@
 
 \indexlibrarymember{notify_one}{atomic_ref<T>}%
 \begin{itemdecl}
-void notify_one() noexcept;
+void notify_one() const noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -1099,7 +1100,7 @@
 
 \indexlibrarymember{notify_all}{atomic_ref<T>}%
 \begin{itemdecl}
-void notify_all() noexcept;
+void notify_all() const noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -1199,8 +1200,8 @@
     @\placeholdernc{integral}@ operator^=(@\placeholdernc{integral}@) const noexcept;
 
     void wait(@\placeholdernc{integral}@, memory_order = memory_order::seq_cst) const noexcept;
-    void notify_one() noexcept;
-    void notify_all() noexcept;
+    void notify_one() const noexcept;
+    void notify_all() const noexcept;
   };
 }
 \end{codeblock}
@@ -1297,7 +1298,7 @@
     atomic_ref& operator=(const atomic_ref&) = delete;
 
     void store(@\placeholdernc{floating-point}@, memory_order = memory_order_seq_cst) const noexcept;
-    @\placeholder{floating-point}@ operator=(@\placeholder{floating-point}@) noexcept;
+    @\placeholder{floating-point}@ operator=(@\placeholder{floating-point}@) const noexcept;
     @\placeholder{floating-point}@ load(memory_order = memory_order_seq_cst) const noexcept;
     operator @\placeholdernc{floating-point}@() const noexcept;
 
@@ -1321,8 +1322,8 @@
     @\placeholder{floating-point}@ operator-=(@\placeholder{floating-point}@) const noexcept;
 
     void wait(@\placeholdernc{floating-point}@, memory_order = memory_order::seq_cst) const noexcept;
-    void notify_one() noexcept;
-    void notify_all() noexcept;
+    void notify_one() const noexcept;
+    void notify_all() const noexcept;
   };
 }
 \end{codeblock}
@@ -1428,8 +1429,8 @@
     T* operator-=(difference_type) const noexcept;
 
     void wait(T*, memory_order = memory_order::seq_cst) const noexcept;
-    void notify_one() noexcept;
-    void notify_all() noexcept;
+    void notify_one() const noexcept;
+    void notify_all() const noexcept;
   };
 }
 \end{codeblock}
@@ -1492,7 +1493,7 @@
 \indexlibrarymember{operator++}{atomic_ref<T*>}%
 \indexlibrarymember{operator++}{atomic_ref<\placeholder{integral}>}%
 \begin{itemdecl}
-T* operator++(int) const noexcept;
+value_type operator++(int) const noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -1504,7 +1505,7 @@
 \indexlibrarymember{operator\dcr}{atomic_ref<T*>}%
 \indexlibrarymember{operator\dcr}{atomic_ref<\placeholder{integral}>}%
 \begin{itemdecl}
-T* operator--(int) const noexcept;
+value_type operator--(int) const noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -1516,7 +1517,7 @@
 \indexlibrarymember{operator++}{atomic_ref<T*>}%
 \indexlibrarymember{operator++}{atomic_ref<\placeholder{integral}>}%
 \begin{itemdecl}
-T* operator++() const noexcept;
+value_type operator++() const noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -1528,7 +1529,7 @@
 \indexlibrarymember{operator\dcr}{atomic_ref<T*>}%
 \indexlibrarymember{operator\dcr}{atomic_ref<\placeholder{integral}>}%
 \begin{itemdecl}
-T* operator--(int) const noexcept;
+value_type operator--() const noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -2608,8 +2609,8 @@
 \indexlibrarymember{operator++}{atomic<T*>}%
 \indexlibrarymember{operator++}{atomic<\placeholder{integral}>}%
 \begin{itemdecl}
-T operator++(int) volatile noexcept;
-T operator++(int) noexcept;
+value_type operator++(int) volatile noexcept;
+value_type operator++(int) noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -2621,8 +2622,8 @@
 \indexlibrarymember{operator\dcr}{atomic<T*>}%
 \indexlibrarymember{operator\dcr}{atomic<\placeholder{integral}>}%
 \begin{itemdecl}
-T operator--(int) volatile noexcept;
-T operator--(int) noexcept;
+value_type operator--(int) volatile noexcept;
+value_type operator--(int) noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -2634,8 +2635,8 @@
 \indexlibrarymember{operator++}{atomic<T*>}%
 \indexlibrarymember{operator++}{atomic<\placeholder{integral}>}%
 \begin{itemdecl}
-T operator++() volatile noexcept;
-T operator++() noexcept;
+value_type operator++() volatile noexcept;
+value_type operator++() noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -2647,8 +2648,8 @@
 \indexlibrarymember{operator\dcr}{atomic<T*>}%
 \indexlibrarymember{operator\dcr}{atomic<\placeholder{integral}>}%
 \begin{itemdecl}
-T operator--() volatile noexcept;
-T operator--() noexcept;
+value_type operator--() volatile noexcept;
+value_type operator--() noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}

source/threads.tex

@@ -5289,16 +5289,20 @@
 \begin{itemdescr}
 \pnum
 \effects
-\begin{itemize}
-\item
-  With low probability, returns immediately.
-  An implementation should ensure
-  that \tcode{try_acquire} does not consistently return \tcode{false}
-  in the absence of contending acquisitions.
-\item
-  Otherwise, atomically check whether \tcode{counter} is greater than zero and,
-  if so, decrement \tcode{counter} by one.
-\end{itemize}
+Attempts to atomically decrement \tcode{counter} if it is positive,
+without blocking.
+If \tcode{counter} is not decremented, there is no effect and
+\tcode{try_acquire} immediately returns.
+An implementation may fail to decrement \tcode{counter}
+even if it is positive.
+\begin{note}
+This spurious failure is normally uncommon, but
+allows interesting implementations
+based on a simple compare and exchange\iref{atomics}.
+\end{note}
+An implementation should ensure that \tcode{try_acquire}
+does not consistently return \tcode{false}
+in the absence of contending semaphore operations.
 
 \pnum
 \returns