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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.
This commit is contained in:
Thomas Rodgers 2022-01-31 13:39:44 -08:00
parent 3ad29854f0
commit 07a971b28c
1 changed files with 6 additions and 6 deletions
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12
libstdc++-v3/include/bits/atomic_wait.h
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@ -209,18 +209,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
void void
_M_enter_wait() noexcept _M_enter_wait() noexcept
{ __atomic_fetch_add(&_M_wait, 1, __ATOMIC_ACQ_REL); } { __atomic_fetch_add(&_M_wait, 1, __ATOMIC_SEQ_CST); }
void void
_M_leave_wait() noexcept _M_leave_wait() noexcept
{ __atomic_fetch_sub(&_M_wait, 1, __ATOMIC_ACQ_REL); } { __atomic_fetch_sub(&_M_wait, 1, __ATOMIC_RELEASE); }
bool bool
_M_waiting() const noexcept _M_waiting() const noexcept
{ {
__platform_wait_t __res; __platform_wait_t __res;
__atomic_load(&_M_wait, &__res, __ATOMIC_ACQUIRE); __atomic_load(&_M_wait, &__res, __ATOMIC_SEQ_CST);
return __res > 0; return __res != 0;
} }
void void
@ -258,7 +258,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
__platform_wait(__addr, __old); __platform_wait(__addr, __old);
#else #else
__platform_wait_t __val; __platform_wait_t __val;
__atomic_load(__addr, &__val, __ATOMIC_RELAXED); __atomic_load(__addr, &__val, __ATOMIC_SEQ_CST);
if (__val == __old) if (__val == __old)
{ {
lock_guard<mutex> __l(_M_mtx); lock_guard<mutex> __l(_M_mtx);
@ -309,7 +309,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{ {
if (_M_laundered()) if (_M_laundered())
{ {
__atomic_fetch_add(_M_addr, 1, __ATOMIC_ACQ_REL); __atomic_fetch_add(_M_addr, 1, __ATOMIC_SEQ_CST);
__all = true; __all = true;
} }
_M_w._M_notify(_M_addr, __all, __bare); _M_w._M_notify(_M_addr, __all, __bare);