[committed] libstdc++: Make std::jthread support pointers to member functions [PR 100612]

[Jonathan Wakely]

This adds a non-standard extension to support initializing a
std::jthread with a pointer to a member function that expects a
stop_token to be added to the arguments. That use case is not supported
by C++20, because the stop_token would get added as the first argument,
which is where the object argument needs to be to invoke a pointer to
member function.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/ChangeLog:

	PR libstdc++/100612
	* include/std/thread (__pmf_expects_stop_token): New variable
	template to detect a pointer to member function that needs a
	stop_token to be added to the arguments.
	(jthread::__S_create): Use __pmf_expects_stop_token.
	(jthread::__S_create_pmf): New function.
	* testsuite/30_threads/jthread/100612.cc: New test.

Tested powerpc64le-linux. Committed to trunk.

-------------- next part --------------
commit 34e9407b3b4298bd587e0df2e0047679019b66cf
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu May 20 22:36:16 2021

    libstdc++: Make std::jthread support pointers to member functions [PR 100612]
    
    This adds a non-standard extension to support initializing a
    std::jthread with a pointer to a member function that expects a
    stop_token to be added to the arguments. That use case is not supported
    by C++20, because the stop_token would get added as the first argument,
    which is where the object argument needs to be to invoke a pointer to
    member function.
    
    Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/100612
            * include/std/thread (__pmf_expects_stop_token): New variable
            template to detect a pointer to member function that needs a
            stop_token to be added to the arguments.
            (jthread::__S_create): Use __pmf_expects_stop_token.
            (jthread::__S_create_pmf): New function.
            * testsuite/30_threads/jthread/100612.cc: New test.

diff --git a/libstdc++-v3/include/std/thread b/libstdc++-v3/include/std/thread
index f51392ab42c..46519086aae 100644
--- a/libstdc++-v3/include/std/thread
+++ b/libstdc++-v3/include/std/thread
@@ -99,6 +99,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #ifdef __cpp_lib_jthread
 
+#ifndef __STRICT_ANSI__
+    template<typename _Callable, typename... _Args>
+      constexpr bool __pmf_expects_stop_token = false;
+
+    template<typename _Callable, typename _Obj, typename... _Args>
+      constexpr bool __pmf_expects_stop_token<_Callable, _Obj, _Args...>
+	= __and_<is_member_function_pointer<remove_reference_t<_Callable>>,
+		 is_invocable<_Callable, _Obj, stop_token, _Args...>>::value;
+#endif
+
   /// A thread that can be requested to stop and automatically joined.
   class jthread
   {
@@ -211,6 +221,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       static thread
       _S_create(stop_source& __ssrc, _Callable&& __f, _Args&&... __args)
       {
+#ifndef __STRICT_ANSI__
+	if constexpr (__pmf_expects_stop_token<_Callable, _Args...>)
+	  return _S_create_pmf(__ssrc, __f, std::forward<_Args>(__args)...);
+	else
+#endif
 	if constexpr(is_invocable_v<decay_t<_Callable>, stop_token,
 				    decay_t<_Args>...>)
 	  return thread{std::forward<_Callable>(__f), __ssrc.get_token(),
@@ -226,6 +241,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  }
       }
 
+#ifndef __STRICT_ANSI__
+    template<typename _Callable, typename _Obj, typename... _Args>
+      static thread
+      _S_create_pmf(stop_source& __ssrc, _Callable __f, _Obj&& __obj,
+		    _Args&&... __args)
+      {
+	return thread{__f, std::forward<_Obj>(__obj), __ssrc.get_token(),
+		      std::forward<_Args>(__args)...};
+      }
+#endif
+
     stop_source _M_stop_source;
     thread _M_thread;
   };
diff --git a/libstdc++-v3/testsuite/30_threads/jthread/100612.cc b/libstdc++-v3/testsuite/30_threads/jthread/100612.cc
new file mode 100644
index 00000000000..d6c81706b8f
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/jthread/100612.cc
@@ -0,0 +1,24 @@
+// { dg-options "-std=gnu++20" }
+// { dg-do compile { target c++20 } }
+// { dg-additional-options "-pthread" { target pthread } }
+// { dg-require-gthreads "" }
+
+#include <thread>
+
+void
+test_pfm()
+{
+  // PR libstdc++/100612
+  struct X
+  {
+    void run(std::stop_token) { }
+    void run_arg(int) { }
+    void run_args(std::stop_token, int, int) { }
+  };
+
+  X x;
+
+  std::jthread{&X::run, &x};
+  std::jthread{&X::run_arg, &x, 1};
+  std::jthread{&X::run_args, &x, 1, 1};
+}