From: Thomas Rodgers <rodgert@appliantology.com>
Date: Thu, 10 Feb 2022 18:12:36 +0000 (-0800)
Subject: libstdc++: Strengthen memory order for atomic<T>::wait/notify
X-Git-Tag: basepoints/gcc-13~1127
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b25a7c05f120e46a60430dcefe529c72303b7022;p=thirdparty%2Fgcc.git

libstdc++: Strengthen memory order for atomic<T>::wait/notify

This changes the memory order used in the spin wait code to match
that of libc++.

libstdc++-v3/ChangeLog:
	* include/bits/atomic_wait.h (__waiter_base::_S_do_spin,
	__waiter_base::_S_do_spin_v): Change memory order from relaxed
	to acquire.
---

diff --git a/libstdc++-v3/include/bits/atomic_wait.h b/libstdc++-v3/include/bits/atomic_wait.h
index 6ce7f9343cf5..125b1cad8868 100644
--- a/libstdc++-v3/include/bits/atomic_wait.h
+++ b/libstdc++-v3/include/bits/atomic_wait.h
@@ -332,7 +332,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	      }
 	    else
 	      {
-		__atomic_load(__addr, &__val, __ATOMIC_RELAXED);
+		__atomic_load(__addr, &__val, __ATOMIC_ACQUIRE);
 	      }
 	    return __atomic_spin(__pred, __spin);
 	  }
@@ -353,7 +353,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 		     __platform_wait_t& __val,
 		     _Spin __spin = _Spin{ })
 	  {
-	    __atomic_load(__addr, &__val, __ATOMIC_RELAXED);
+	    __atomic_load(__addr, &__val, __ATOMIC_ACQUIRE);
 	    return __atomic_spin(__pred, __spin);
 	  }