[PATCH] Add support for atomic_flag::wait/notify_one/notify_all

[Thomas Rodgers]

	* include/bits/atomic_base.h (__atomic_flag::wait): Define.
	(__atomic_flag::notify_one): Likewise.
	(__atomic_flag::notify_all): Likewise.
	* testsuite/29_atomics/atomic_flag/wait_notify/1.cc: New test.
---
 libstdc++-v3/include/bits/atomic_base.h       | 23 +++++++
 .../29_atomics/atomic_flag/wait_notify/1.cc   | 61 +++++++++++++++++++
 2 files changed, 84 insertions(+)
 create mode 100644 libstdc++-v3/testsuite/29_atomics/atomic_flag/wait_notify/1.cc

diff --git a/libstdc++-v3/include/bits/atomic_base.h b/libstdc++-v3/include/bits/atomic_base.h
index c121d993fee..a7ddd03d544 100644
--- a/libstdc++-v3/include/bits/atomic_base.h
+++ b/libstdc++-v3/include/bits/atomic_base.h
@@ -229,6 +229,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       __atomic_load(&_M_i, &__v, int(__m));
       return __v == __GCC_ATOMIC_TEST_AND_SET_TRUEVAL;
     }
+
+    _GLIBCXX_ALWAYS_INLINE void
+    wait(bool __old,
+	memory_order __m = memory_order_seq_cst) const noexcept
+    {
+      std::__atomic_wait(&_M_i, __old,
+			 [__m, this, __old]()
+			 { return this->test(__m) != __old; });
+    }
+
+    // TODO add const volatile overload
+
+    _GLIBCXX_ALWAYS_INLINE void
+    notify_one() const noexcept
+    { std::__atomic_notify(&_M_i, false); }
+
+    // TODO add const volatile overload
+
+    _GLIBCXX_ALWAYS_INLINE void
+    notify_all() const noexcept
+    { std::__atomic_notify(&_M_i, true); }
+
+    // TODO add const volatile overload
 #endif // C++20
 
     _GLIBCXX_ALWAYS_INLINE void
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_flag/wait_notify/1.cc b/libstdc++-v3/testsuite/29_atomics/atomic_flag/wait_notify/1.cc
new file mode 100644
index 00000000000..6de7873ecc2
--- /dev/null
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_flag/wait_notify/1.cc
@@ -0,0 +1,61 @@
+// { dg-options "-std=gnu++2a -pthread" }
+// { dg-do run { target c++2a } }
+// { dg-require-effective-target pthread }
+// { dg-require-gthreads "" }
+
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <atomic>
+#include <chrono>
+#include <condition_variable>
+#include <concepts>
+#include <mutex>
+#include <thread>
+
+#include <testsuite_hooks.h>
+
+int
+main()
+{
+  using namespace std::literals::chrono_literals;
+
+  std::mutex m;
+  std::condition_variable cv;
+
+  std::atomic_flag a;
+  std::atomic_flag b;
+  std::thread t([&]
+		{
+		  cv.notify_one();
+		  a.wait(false);
+                  b.test_and_set();
+                  b.notify_one();
+		});
+
+  std::unique_lock<std::mutex> l(m);
+  cv.wait(l);
+  std::this_thread::sleep_for(100ms);
+  a.test_and_set();
+  a.notify_one();
+  b.wait(false);
+  t.join();
+
+  VERIFY( a.test() );
+  VERIFY( b.test() );
+  return 0;
+}
-- 
2.26.2