Do not copy std:call_once arguments (LWG 2442)

	* doc/xml/manual/intro.xml: Document LWG 2442 status.
	* include/std/mutex [_GLIBCXX_HAVE_TLS] (__once_call_impl): Remove.
	[_GLIBCXX_HAVE_TLS] (_Once_call): Declare primary template and define
	partial specialization to unpack args and forward to std::invoke.
	(call_once) [_GLIBCXX_HAVE_TLS]: Use forward_as_tuple and _Once_call
	instead of __bind_simple and __once_call_impl.
	(call_once) [!_GLIBCXX_HAVE_TLS]: Use __invoke instead of
	__bind_simple.
	* testsuite/30_threads/call_once/dr2442.cc: New test.

From-SVN: r241031

1 files changed, 23 insertions, 12 deletions

diff --git a/libstdc++-v3/include/std/mutex b/libstdc++-v3/include/std/mutex
index 7a7bd2e..4c6f036 100644
--- a/libstdc++-v3/include/std/mutex
+++ b/libstdc++-v3/include/std/mutex
@@ -580,12 +580,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   extern __thread void* __once_callable;
   extern __thread void (*__once_call)();
 
-  template<typename _Callable>
-    inline void
-    __once_call_impl()
+  template<typename _Tuple, typename _IndexSeq
+	   = typename _Build_index_tuple<tuple_size<_Tuple>::value>::__type>
+    struct _Once_call;
+
+  template<typename _Tuple, size_t... _Ind>
+    struct _Once_call<_Tuple, _Index_tuple<_Ind...>>
     {
-      (*(_Callable*)__once_callable)();
-    }
+      static void
+      _S_call()
+      {
+	auto& __f_args = *static_cast<_Tuple*>(__once_callable);
+	std::__invoke(std::get<_Ind>(std::move(__f_args))...);
+      }
+    };
 #else
   extern function<void()> __once_functor;
 
@@ -603,16 +611,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     void
     call_once(once_flag& __once, _Callable&& __f, _Args&&... __args)
     {
+      // _GLIBCXX_RESOLVE_LIB_DEFECTS
+      // 2442. call_once() shouldn't DECAY_COPY()
 #ifdef _GLIBCXX_HAVE_TLS
-      auto __bound_functor = std::__bind_simple(std::forward<_Callable>(__f),
-          std::forward<_Args>(__args)...);
-      __once_callable = std::__addressof(__bound_functor);
-      __once_call = &__once_call_impl<decltype(__bound_functor)>;
+      auto __f_args = std::forward_as_tuple(
+	  std::forward<_Callable>(__f), std::forward<_Args>(__args)...);
+      __once_callable = std::__addressof(__f_args);
+      __once_call = _Once_call<decltype(__f_args)>::_S_call;
 #else
       unique_lock<mutex> __functor_lock(__get_once_mutex());
-      auto __callable = std::__bind_simple(std::forward<_Callable>(__f),
-          std::forward<_Args>(__args)...);
-      __once_functor = [&]() { __callable(); };
+      __once_functor = [&] {
+	  std::__invoke(std::forward<_Callable>(__f),
+			std::forward<_Args>(__args)...);
+      };
       __set_once_functor_lock_ptr(&__functor_lock);
 #endif