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From: Thomas Rodgers <rodgertq@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r12-6964] Strengthen memory order for atomic<T>::wait/notify Date: Tue, 1 Feb 2022 17:04:32 +0000 (GMT) [thread overview] Message-ID: <20220201170432.DFE0C3858C74@sourceware.org> (raw) https://gcc.gnu.org/g:07a971b28c880938bb7e070465ab8ee6ccdad1fb commit r12-6964-g07a971b28c880938bb7e070465ab8ee6ccdad1fb Author: Thomas Rodgers <rodgert@appliantology.com> Date: Mon Jan 31 13:39:44 2022 -0800 Strengthen memory order for atomic<T>::wait/notify This matches the memory order in libc++. libstdc++-v3/ChangeLog: * include/bits/atomic_wait.h: Change memory order from Acquire/Release with relaxed loads to SeqCst+Release for accesses to the waiter's count. Diff: --- libstdc++-v3/include/bits/atomic_wait.h | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/libstdc++-v3/include/bits/atomic_wait.h b/libstdc++-v3/include/bits/atomic_wait.h index 05cf0013d2a..d7de0d7eb9e 100644 --- a/libstdc++-v3/include/bits/atomic_wait.h +++ b/libstdc++-v3/include/bits/atomic_wait.h @@ -209,18 +209,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION void _M_enter_wait() noexcept - { __atomic_fetch_add(&_M_wait, 1, __ATOMIC_ACQ_REL); } + { __atomic_fetch_add(&_M_wait, 1, __ATOMIC_SEQ_CST); } void _M_leave_wait() noexcept - { __atomic_fetch_sub(&_M_wait, 1, __ATOMIC_ACQ_REL); } + { __atomic_fetch_sub(&_M_wait, 1, __ATOMIC_RELEASE); } bool _M_waiting() const noexcept { __platform_wait_t __res; - __atomic_load(&_M_wait, &__res, __ATOMIC_ACQUIRE); - return __res > 0; + __atomic_load(&_M_wait, &__res, __ATOMIC_SEQ_CST); + return __res != 0; } void @@ -258,7 +258,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION __platform_wait(__addr, __old); #else __platform_wait_t __val; - __atomic_load(__addr, &__val, __ATOMIC_RELAXED); + __atomic_load(__addr, &__val, __ATOMIC_SEQ_CST); if (__val == __old) { lock_guard<mutex> __l(_M_mtx); @@ -309,7 +309,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { if (_M_laundered()) { - __atomic_fetch_add(_M_addr, 1, __ATOMIC_ACQ_REL); + __atomic_fetch_add(_M_addr, 1, __ATOMIC_SEQ_CST); __all = true; } _M_w._M_notify(_M_addr, __all, __bare);
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