[PATCH] Add c++2a binary_semaphore

[Thomas Rodgers <trodgers@redhat.com>]

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This patch adds the c++2a semaphore header and binary_semaphore type. The implementation is not complete, this patch is just to solicit initial feedback.

        * include/std/semaphore: New file.
	* include/std/version (__cpp_lib_semaphore): Add feature test macro.
	* include/Makefile.am (std_headers): add semaphore.
	* include/Makefile.in: Regenerate.
	* testsuite/30_threads/semaphore/1.cc: New test.
	* testsuite/30_threads/semaphore/2.cc: New test.
	* testsuite/30_threads/semaphore/binary_semaphore.cc: New test.
	* testsuite/30_threads/semaphore/try_acquire.cc: New test.
	* testsuite/30_threads/semaphore/try_acquire_for.cc: New test.
	* testsuite/30_threads/semaphore/try_acquire_until.cc: New test.


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From 8ce4252605361ed33b389a91fb7e3aeec529d9ac Mon Sep 17 00:00:00 2001
From: Thomas Rodgers <rodgert@thufir.appliantology.local>
Date: Mon, 17 Feb 2020 19:58:57 -0800
Subject: [PATCH] Add c++2a binary_semaphore

    * include/std/semaphore: New file.
    * include/std/version (__cpp_lib_semaphore): Add feature test macro.
    * include/Makefile.am (std_headers): add semaphore.
    * include/Makefile.in: Regenerate.
    * testsuite/30_threads/semaphore/1.cc: New test.
    * testsuite/30_threads/semaphore/2.cc: New test.
    * testsuite/30_threads/semaphore/binary_semaphore.cc: New test.
    * testsuite/30_threads/semaphore/try_acquire.cc: New test.
    * testsuite/30_threads/semaphore/try_acquire_for.cc: New test.
    * testsuite/30_threads/semaphore/try_acquire_until.cc: New test.
---
 libstdc++-v3/include/Makefile.am              |   1 +
 libstdc++-v3/include/Makefile.in              |   1 +
 libstdc++-v3/include/std/semaphore            | 131 ++++++++++++++++++
 libstdc++-v3/include/std/version              |   1 +
 .../testsuite/30_threads/semaphore/1.cc       |  27 ++++
 .../testsuite/30_threads/semaphore/2.cc       |  27 ++++
 .../30_threads/semaphore/binary_semaphore.cc  |  47 +++++++
 .../30_threads/semaphore/try_acquire.cc       |  36 +++++
 .../30_threads/semaphore/try_acquire_for.cc   |  72 ++++++++++
 .../30_threads/semaphore/try_acquire_until.cc |  74 ++++++++++
 10 files changed, 417 insertions(+)
 create mode 100644 libstdc++-v3/include/std/semaphore
 create mode 100644 libstdc++-v3/testsuite/30_threads/semaphore/1.cc
 create mode 100644 libstdc++-v3/testsuite/30_threads/semaphore/2.cc
 create mode 100644 libstdc++-v3/testsuite/30_threads/semaphore/binary_semaphore.cc
 create mode 100644 libstdc++-v3/testsuite/30_threads/semaphore/try_acquire.cc
 create mode 100644 libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_for.cc
 create mode 100644 libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_until.cc

diff --git a/libstdc++-v3/include/Makefile.am b/libstdc++-v3/include/Makefile.am
index 89835759069..2dbb7d3a6b1 100644
--- a/libstdc++-v3/include/Makefile.am
+++ b/libstdc++-v3/include/Makefile.am
@@ -69,6 +69,7 @@ std_headers = \
 	${std_srcdir}/ratio \
 	${std_srcdir}/regex \
 	${std_srcdir}/scoped_allocator \
+  ${std_srcdir}/semaphore \
 	${std_srcdir}/set \
 	${std_srcdir}/shared_mutex \
 	${std_srcdir}/span \
diff --git a/libstdc++-v3/include/Makefile.in b/libstdc++-v3/include/Makefile.in
index 123d24bb1c6..8f2780c86ce 100644
--- a/libstdc++-v3/include/Makefile.in
+++ b/libstdc++-v3/include/Makefile.in
@@ -414,6 +414,7 @@ std_headers = \
 	${std_srcdir}/ratio \
 	${std_srcdir}/regex \
 	${std_srcdir}/scoped_allocator \
+  ${std_srcdir}/semaphore \
 	${std_srcdir}/set \
 	${std_srcdir}/shared_mutex \
 	${std_srcdir}/span \
diff --git a/libstdc++-v3/include/std/semaphore b/libstdc++-v3/include/std/semaphore
new file mode 100644
index 00000000000..e3e88a50eec
--- /dev/null
+++ b/libstdc++-v3/include/std/semaphore
@@ -0,0 +1,131 @@
+// <stop_token> -*- C++ -*-
+
+// Copyright (C) 2019-2020 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.
+
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+// <http://www.gnu.org/licenses/>.
+
+/** @file include/stop_token
+ *  This is a Standard C++ Library header.
+ */
+
+#ifndef _GLIBCXX_SEMAPHORE
+#define _GLIBCXX_SEMAPHORE
+
+#if __cplusplus > 201703L
+#define __cpp_lib_semaphore 201907L
+
+#include <cstddef>
+#include <atomic>
+#include <chrono>
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+  // TODO: replace this with a real implementation of std::binary_semaphore
+  struct binary_semaphore
+{
+  explicit binary_semaphore(int __d) : _M_counter(__d > 0) { }
+
+  static constexpr std::ptrdiff_t
+  max() noexcept
+  {
+   return 1;
+  }
+
+  void release() { _M_counter.fetch_add(1, memory_order::release); }
+
+  void acquire()
+  {
+   while (!_M_try_acquire())
+     {
+      _S_yield();
+     }
+  }
+
+  bool
+  try_acquire() noexcept
+  {
+   return _M_try_acquire(1u);
+  }
+
+  template<class _Rep, class _Period>
+  bool try_acquire_for(const std::chrono::duration<_Rep, _Period>& __rel_time)
+  {
+   auto __abst = std::chrono::steady_clock::now() + __rel_time;
+   return try_acquire_until(__abst);
+  }
+
+  template<class _Clock, class _Duration>
+  bool try_acquire_until(const std::chrono::time_point<_Clock, _Duration>& __abs_time)
+  {
+   do
+     {
+      if (_M_try_acquire())
+        {
+         return true;
+        }
+     } while (std::chrono::steady_clock::now() < __abs_time);
+   return false;
+  }
+
+private:
+  static void
+  _S_yield() noexcept
+  {
+#if defined __i386__ || defined __x86_64__
+   __builtin_ia32_pause();
+#elif defined _GLIBCXX_USE_SCHED_YIELD
+   __gthread_yield();
+#endif
+  }
+
+  bool
+  _M_try_acquire(unsigned __spin_ct)
+  {
+   int __old = 1;
+   while (!_M_counter.compare_exchange_weak(__old, 0,
+                                            memory_order::acquire,
+                                            memory_order::relaxed))
+     {
+       if (--__spin_ct == 0)
+         {
+           return false;
+         }
+      __old = 1;
+     }
+   return true;
+  }
+
+  static constexpr unsigned _S_spin_ct = 64u;
+  bool
+  _M_try_acquire()
+  {
+    return _M_try_acquire(1);
+  }
+
+  atomic<int> _M_counter;
+};
+
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace
+#endif // __cplusplus > 201703L
+#endif // _GLIBCXX_STOP_TOKEN
diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index d8a97767453..4654830b614 100644
--- a/libstdc++-v3/include/std/version
+++ b/libstdc++-v3/include/std/version
@@ -188,6 +188,7 @@
 #define __cpp_lib_interpolate 201902L
 #ifdef _GLIBCXX_HAS_GTHREADS
 # define __cpp_lib_jthread 201907L
+# define __cpp_lib_semaphore 201907L
 #endif
 #define __cpp_lib_list_remove_return_type 201806L
 #define __cpp_lib_math_constants 201907L
diff --git a/libstdc++-v3/testsuite/30_threads/semaphore/1.cc b/libstdc++-v3/testsuite/30_threads/semaphore/1.cc
new file mode 100644
index 00000000000..1bbca687fc3
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/semaphore/1.cc
@@ -0,0 +1,27 @@
+// 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/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <semaphore>
+
+#ifndef __cpp_lib_semaphore
+# error "Feature-test macro for semaphore missing in <semaphore>"
+#elif __cpp_lib_semaphore != 201907L
+# error "Feature-test macro for semaphore has wrong value in <semaphore>"
+#endif
diff --git a/libstdc++-v3/testsuite/30_threads/semaphore/2.cc b/libstdc++-v3/testsuite/30_threads/semaphore/2.cc
new file mode 100644
index 00000000000..b96b8a59c64
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/semaphore/2.cc
@@ -0,0 +1,27 @@
+// Copyright (C) 2019-2020 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/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <version>
+
+#ifndef __cpp_lib_semaphore
+# error "Feature-test macro for semaphore missing in <version>"
+#elif __cpp_lib_semaphore != 201907L
+# error "Feature-test macro for semaphore has wrong value in <version>"
+#endif
diff --git a/libstdc++-v3/testsuite/30_threads/semaphore/binary_semaphore.cc b/libstdc++-v3/testsuite/30_threads/semaphore/binary_semaphore.cc
new file mode 100644
index 00000000000..1a42d323ca0
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/semaphore/binary_semaphore.cc
@@ -0,0 +1,47 @@
+// Copyright (C) 2019-2020 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/>.
+
+// { dg-options "-std=gnu++2a -pthread" }
+// { dg-do run { target c++2a } }
+// { dg-require-effective-target pthread }
+// { dg-require-gthreads "" }
+
+#include <semaphore>
+#include <chrono>
+#include <thread>
+
+#include <testsuite_hooks.h>
+
+int main()
+{
+  std::binary_semaphore s(1);
+
+  auto ar = [&]() {
+              for(auto i = 0u; i < 512; ++i) {
+                s.acquire();
+                std::this_thread::sleep_for(std::chrono::microseconds(1));
+                s.release();
+              }
+            };
+
+  std::thread t(ar);
+  ar();
+
+  t.join();
+
+  return 0;
+}
diff --git a/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire.cc b/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire.cc
new file mode 100644
index 00000000000..295cfa9bca8
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire.cc
@@ -0,0 +1,36 @@
+// Copyright (C) 2019-2020 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/>.
+
+// { dg-options "-std=gnu++2a -pthread" }
+// { dg-do run { target c++2a } }
+// { dg-require-effective-target pthread }
+// { dg-require-gthreads "" }
+
+#include <semaphore>
+
+int main()
+{
+  std::binary_semaphore s(1);
+
+  s.acquire();
+  if (s.try_acquire())
+    return -1;
+  s.release();
+  if (!s.try_acquire())
+    return -1;
+  return 0;
+}
diff --git a/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_for.cc b/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_for.cc
new file mode 100644
index 00000000000..a04b39b5401
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_for.cc
@@ -0,0 +1,72 @@
+// Copyright (C) 2019-2020 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/>.
+
+// { dg-options "-std=gnu++2a -pthread" }
+// { dg-do run { target c++2a } }
+// { dg-require-effective-target pthread }
+// { dg-require-gthreads "" }
+
+#include <semaphore>
+#include <chrono>
+#include <thread>
+#include <mutex>
+#include <condition_variable>
+
+int main()
+{
+  using lock_type = std::unique_lock<std::mutex>;
+
+  bool ready = false;
+  lock_type::mutex_type m;
+  std::condition_variable cv;
+
+  std::binary_semaphore s(1);
+  auto ar =[&] {
+             s.acquire();
+             {
+               lock_type l(m);
+               ready = true;
+             }
+             cv.notify_one();
+             std::this_thread::sleep_for(std::chrono::milliseconds(500));
+             s.release();
+           };
+
+  std::thread t1(ar);
+  {
+    lock_type l(m, std::defer_lock);
+    cv.wait(l, [&] { return ready; });
+
+    if (s.try_acquire_for(std::chrono::milliseconds(100)))
+      return -1;
+    t1.join();
+    if (!s.try_acquire())
+      return -1;
+    s.release();
+    ready = false;
+  }
+
+  std::thread t2(ar);
+  {
+    lock_type l(m, std::defer_lock);
+    cv.wait(l, [&] { return ready; });
+    if (!s.try_acquire_for(std::chrono::milliseconds(1009)))
+      return -1;
+    t2.join();
+  }
+  return 0;
+}
diff --git a/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_until.cc b/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_until.cc
new file mode 100644
index 00000000000..987b655a6da
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/semaphore/try_acquire_until.cc
@@ -0,0 +1,74 @@
+// Copyright (C) 2019-2020 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/>.
+
+// { dg-options "-std=gnu++2a -pthread" }
+// { dg-do run { target c++2a } }
+// { dg-require-effective-target pthread }
+// { dg-require-gthreads "" }
+
+#include <semaphore>
+#include <chrono>
+#include <thread>
+#include <mutex>
+#include <condition_variable>
+
+int main()
+{
+  using lock_type = std::unique_lock<std::mutex>;
+
+  bool ready = false;
+  lock_type::mutex_type m;
+  std::condition_variable cv;
+
+  auto abst = std::chrono::steady_clock::now();
+
+  std::binary_semaphore s(1);
+  auto ar =[&] {
+             s.acquire();
+             {
+               lock_type l(m);
+               ready = true;
+             }
+             cv.notify_one();
+             std::this_thread::sleep_until(abst + std::chrono::milliseconds(500));
+             s.release();
+           };
+
+  std::thread t1(ar);
+  {
+    lock_type l(m, std::defer_lock);
+    cv.wait(l, [&] { return ready; });
+
+    if (s.try_acquire_until(abst + std::chrono::milliseconds(100)))
+      return -1;
+    t1.join();
+    if (!s.try_acquire())
+      return -1;
+    s.release();
+    ready = false;
+  }
+
+  std::thread t2(ar);
+  {
+    lock_type l(m, std::defer_lock);
+    cv.wait(l, [&] { return ready; });
+    if (!s.try_acquire_until(abst + std::chrono::milliseconds(1009)))
+      return -1;
+    t2.join();
+  }
+  return 0;
+}
-- 
2.24.1