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* [gcc r12-62] libstdc++: Fix "bare" notifications dropped by waiters check
@ 2021-04-22 14:34 Thomas Rodgers
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From: Thomas Rodgers @ 2021-04-22 14:34 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:ae2f6e01749f39b8b8ccc211fc29e5e6ec8b57cd
commit r12-62-gae2f6e01749f39b8b8ccc211fc29e5e6ec8b57cd
Author: Thomas Rodgers <rodgert@twrodgers.com>
Date: Wed Apr 21 18:12:03 2021 -0700
libstdc++: Fix "bare" notifications dropped by waiters check
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.
libstdc++-v3/ChangeLog:
* include/bits/atomic_wait.h: Always notify waiters in the
case of 'bare' address notification.
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 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
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