Re: [PATCH] libstdc++: Add missing free functions for atomic_flag [PR103934]

[Thomas Rodgers <trodgers@redhat.com>]

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This patch did not get committed in a timely manner after it was OK'd. In
revisiting the patch some issues were found that have lead me to resubmit
for review -

Specifically -

The original commit to add C++20 atomic_flag::test did not include the free
functions for atomic_flag_test[_explicit]
The original commit to add C++20 atomic_flag::wait/notify did not include
the free functions for atomic_flag_wait/notify[_explicit]

These two commits landed in GCC10 and GCC11 respectively. My original patch
included both sets of free functions, but
that complicates the backporting of these changes to GCC10, GCC11, and
GCC12.

Additionally commit 7c2155 removed const qualification from
atomic_flag::notify_one/notify_all but the original version of this
patch accepts the atomic flag as const.

The original version of this patch did not include test cases for the
atomic_flag_test[_explicit] free functions.

I have split the original patch into two patches, on for the
atomic_flag_test free functions, and one for the atomic_flag_wait/notify
free functions.


On Wed, Feb 2, 2022 at 1:35 PM Jonathan Wakely <jwakely@redhat.com> wrote:

> >+  inline void
> >+  atomic_flag_wait_explicit(const atomic_flag* __a, bool __old,
> >+               std::memory_order __m) noexcept
>
> No need for the std:: qualification, and check the indentation.
>
>
> > libstdc++-v3/ChangeLog:
> >
> >    PR103934
>
> This needs to include the component: PR libstdc++/103934
>
> >    * include/std/atomic: Add missing free functions.
>
> Please name the new functions in the changelog, in the usual format.
> Just the names is fine, no need for the full signatures with
> parameters.
>
> OK for trunk with those changes.
>
>

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From 1338538c1667b7fbe201d22d81254e33a0e7b24c Mon Sep 17 00:00:00 2001
From: Thomas W Rodgers <rodgert@twrodgers.com>
Date: Fri, 10 Feb 2023 10:09:06 -0800
Subject: [PATCH 2/2] libstdc++: Add missing free functions for atomic_flag
 [PR103934]

This patch adds -
  atomic_flag_wait
  atomic_flag_wait_explicit
  atomic_flag_notify
  atomic_flag_notify_explicit

Which were missed when commit 83a1be introduced C++20 atomic wait.

libstdc++-v3/ChangeLog:

	PR libstdc++/103934
	* include/std/atomic: Add missing free functions.
	* testsuite/29_atomics/atomic_flag/wait_notify/1.cc:
	Add test case to cover missing atomic_flag free functions.
---
 libstdc++-v3/include/std/atomic               | 19 ++++++++++++++
 .../29_atomics/atomic_flag/wait_notify/1.cc   | 26 +++++++++++++++++--
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/std/atomic b/libstdc++-v3/include/std/atomic
index 1edd3ae16fa..e82a6427378 100644
--- a/libstdc++-v3/include/std/atomic
+++ b/libstdc++-v3/include/std/atomic
@@ -1259,6 +1259,25 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   atomic_flag_clear(volatile atomic_flag* __a) noexcept
   { atomic_flag_clear_explicit(__a, memory_order_seq_cst); }
 
+#if __cpp_lib_atomic_wait
+  inline void
+      atomic_flag_wait(atomic_flag* __a, bool __old) noexcept
+  { __a->wait(__old); }
+
+  inline void
+      atomic_flag_wait_explicit(atomic_flag* __a, bool __old,
+                                memory_order __m) noexcept
+  { __a->wait(__old, __m); }
+
+  inline void
+      atomic_flag_notify_one(atomic_flag* __a) noexcept
+  { __a->notify_one(); }
+
+  inline void
+      atomic_flag_notify_all(atomic_flag* __a) noexcept
+  { __a->notify_all(); }
+#endif // __cpp_lib_atomic_wait
+
   /// @cond undocumented
   // _GLIBCXX_RESOLVE_LIB_DEFECTS
   // 3220. P0558 broke conforming C++14 uses of atomic shared_ptr
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
index 240fb4259f7..777fa915ea1 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic_flag/wait_notify/1.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_flag/wait_notify/1.cc
@@ -26,8 +26,8 @@
 
 #include <testsuite_hooks.h>
 
-int
-main()
+void
+test01()
 {
   std::atomic_flag a;
   VERIFY( !a.test() );
@@ -39,5 +39,27 @@ main()
     });
   a.wait(false);
   t.join();
+}
+
+void
+test02()
+{
+  std::atomic_flag a;
+  VERIFY( !std::atomic_flag_test(&a) );
+  std::atomic_flag_wait(&a, true);
+  std::thread t([&]
+    {
+      std::atomic_flag_test_and_set(&a);
+      std::atomic_flag_notify_one(&a);
+    });
+    std::atomic_flag_wait(&a, false);
+    t.join();
+}
+
+int
+main()
+{
+  test01();
+  test02();
   return 0;
 }
-- 
2.39.1


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From 7f21e98bbefde5437a116ccda35a85922f5882bf Mon Sep 17 00:00:00 2001
From: Thomas W Rodgers <rodgert@twrodgers.com>
Date: Fri, 10 Feb 2023 09:35:11 -0800
Subject: [PATCH 1/2] libstdc++: Add missing free functions for atomic_flag
 [PR103934]

This patch adds -
  atomic_flag_test
  atomic_flag_test_explicit

Which were missed when commit 491ba6 introduced C++20 atomic flag
test.

libstdc++-v3/ChangeLog:

	PR libstdc++/103934
	* include/std/atomic: Add missing free functions.
	* testsuite/29_atomics/atomic_flag/test/explicit.cc
        Add test case to cover missing atomic_flag free functions.
        * testsuite/29_atomics/atomic_flag/test/explicit.cc
        Likewise.
---
 libstdc++-v3/include/std/atomic               | 20 ++++++++++++++
 .../29_atomics/atomic_flag/test/explicit.cc   | 26 ++++++++++++++++++-
 .../29_atomics/atomic_flag/test/implicit.cc   | 26 ++++++++++++++++++-
 3 files changed, 70 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/std/atomic b/libstdc++-v3/include/std/atomic
index 1c27c8c41e1..1edd3ae16fa 100644
--- a/libstdc++-v3/include/std/atomic
+++ b/libstdc++-v3/include/std/atomic
@@ -1214,6 +1214,26 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 				    memory_order __m) noexcept
   { return __a->test_and_set(__m); }
 
+#if __cpp_lib_atomic_flag_test
+  inline bool
+  atomic_flag_test(const atomic_flag* __a) noexcept
+  { return __a->test(); }
+
+  inline bool
+  atomic_flag_test(const volatile atomic_flag* __a) noexcept
+  { return __a->test(); }
+
+  inline bool
+  atomic_flag_test_explicit(const atomic_flag* __a,
+			    memory_order __m) noexcept
+  { return __a->test(__m); }
+
+  inline bool
+  atomic_flag_test_explicit(const volatile atomic_flag* __a,
+			    memory_order __m) noexcept
+  { return __a->test(__m); }
+#endif
+
   inline void
   atomic_flag_clear_explicit(atomic_flag* __a, memory_order __m) noexcept
   { __a->clear(__m); }
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/explicit.cc b/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/explicit.cc
index 380bd36ac47..fc8d6589707 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/explicit.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/explicit.cc
@@ -22,7 +22,8 @@
 #include <atomic>
 #include <testsuite_hooks.h>
 
-int main()
+void
+test01()
 {
   using namespace std;
 
@@ -38,3 +39,26 @@ int main()
   VERIFY( ! af.test(memory_order_acquire) );
   VERIFY( ! caf.test(memory_order_acquire) );
 }
+
+void
+test02()
+{
+  using namespace std;
+
+  atomic_flag af{true};
+  const atomic_flag& caf = af;
+
+  VERIFY( atomic_flag_test_explicit(&af, memory_order_acquire) );
+  VERIFY( atomic_flag_test_explicit(&caf, memory_order_acquire) );
+  af.clear(memory_order_release);
+  VERIFY( ! atomic_flag_test_explicit(&af, memory_order_acquire) );
+  VERIFY( ! atomic_flag_test_explicit(&caf, memory_order_acquire) );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  return 0;
+}
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/implicit.cc b/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/implicit.cc
index cce873fa553..2840055433f 100644
--- a/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/implicit.cc
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_flag/test/implicit.cc
@@ -22,7 +22,8 @@
 #include <atomic>
 #include <testsuite_hooks.h>
 
-int main()
+void
+test01()
 {
   using namespace std;
 
@@ -38,3 +39,26 @@ int main()
   VERIFY( ! af.test() );
   VERIFY( ! caf.test() );
 }
+
+void
+test02()
+{
+  using namespace std;
+
+  atomic_flag af{true};
+  const atomic_flag& caf = af;
+
+  VERIFY( atomic_flag_test(&af) );
+  VERIFY( atomic_flag_test(&caf) );
+  af.clear(memory_order_release);
+  VERIFY( ! atomic_flag_test(&af) );
+  VERIFY( ! atomic_flag_test(&caf) );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  return 0;
+}
-- 
2.39.1