On Thu, Apr 22, 2021 at 4:29 AM Thomas Rodgers <rodg...@appliantology.com> wrote: > > From: Thomas Rodgers <rodg...@twrodgers.com> > > NOTE - This patch also needs to be backported to gcc-11 in order for > semaphore release() to work correctly on non-futex platforms. > > Tested sparc-sun-solaris2.11 > > For types that track whether or not there extant waiters (e.g. > semaphore) internally, the __atomic_notify_address_bare() call was > introduced to avoid the overhead of loading the atomic count of > waiters. For platforms that don't have Futex, however, there was > still a check for waiters, and seeing that there are none (because > in the bare case, the count is not incremented), the notification > is dropped. This commit addresses that case.
This is OK for the GCC 11 branch if approved for trunk. Richard. > libstdc++-v3/ChangeLog: > * include/bits/atomic_wait.h: Always notify waiters in the > in the case of 'bare' address notification. > --- > 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 0ac5575190c..984ed70f16c 100644 > --- a/libstdc++-v3/include/bits/atomic_wait.h > +++ b/libstdc++-v3/include/bits/atomic_wait.h > @@ -226,9 +226,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > } > > void > - _M_notify(const __platform_wait_t* __addr, bool __all) noexcept > + _M_notify(const __platform_wait_t* __addr, bool __all, bool __bare) > noexcept > { > - if (!_M_waiting()) > + if (!(__bare || _M_waiting())) > return; > > #ifdef _GLIBCXX_HAVE_PLATFORM_WAIT > @@ -304,11 +304,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > } > > void > - _M_notify(bool __all) > + _M_notify(bool __all, bool __bare = false) > { > if (_M_addr == &_M_w._M_ver) > __atomic_fetch_add(_M_addr, 1, __ATOMIC_ACQ_REL); > - _M_w._M_notify(_M_addr, __all); > + _M_w._M_notify(_M_addr, __all, __bare); > } > > template<typename _Up, typename _ValFn, > @@ -452,7 +452,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > __atomic_notify_address(const _Tp* __addr, bool __all) noexcept > { > __detail::__bare_wait __w(__addr); > - __w._M_notify(__all); > + __w._M_notify(__all, true); > } > > // This call is to be used by atomic types which track contention > externally > @@ -464,7 +464,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > __detail::__platform_notify(__addr, __all); > #else > __detail::__bare_wait __w(__addr); > - __w._M_notify(__all); > + __w._M_notify(__all, true); > #endif > } > _GLIBCXX_END_NAMESPACE_VERSION > -- > 2.30.2 >