On 2021-05-17 09:43, Jonathan Wakely wrote:
On 14/05/21 18:09 +0100, Jonathan Wakely wrote: On 13/05/21 18:54
-0700, Thomas Rodgers wrote: From: Thomas Rodgers
<rodg...@twrodgers.com>
Please ignore the previous patch. This one removes the need to carry
any
extra state in the case of a 'laundered' atomic wait.
libstdc++/ChangeLog:
* include/bits/atomic_wait.h (__waiter::_M_do_wait_v): loop
until value change observed.
(__waiter_base::_M_laundered): New member function.
(__watier_base::_M_notify): Check _M_laundered() to determine
whether to wake one or all.
(__detail::__atomic_compare): Return true if call to
__builtin_memcmp() == 0.
(__waiter_base::_S_do_spin_v): Adjust predicate.
* testsuite/29_atomics/atomic/wait_notify/100334.cc: New
test.
---
libstdc++-v3/include/bits/atomic_wait.h | 28 ++++--
.../29_atomics/atomic/wait_notify/100334.cc | 94 +++++++++++++++++++
2 files changed, 114 insertions(+), 8 deletions(-)
create mode 100644
libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/100334.cc
diff --git a/libstdc++-v3/include/bits/atomic_wait.h
b/libstdc++-v3/include/bits/atomic_wait.h
index 984ed70f16c..07bb744d822 100644
--- a/libstdc++-v3/include/bits/atomic_wait.h
+++ b/libstdc++-v3/include/bits/atomic_wait.h
@@ -181,11 +181,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return false;
}
+ // return true if equal
template<typename _Tp>
bool __atomic_compare(const _Tp& __a, const _Tp& __b)
{
// TODO make this do the correct padding bit ignoring comparison
- return __builtin_memcmp(&__a, &__b, sizeof(_Tp)) != 0;
+ return __builtin_memcmp(&__a, &__b, sizeof(_Tp)) == 0;
}
struct __waiter_pool_base
@@ -300,14 +301,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
explicit __waiter_base(const _Up* __addr) noexcept
: _M_w(_S_for(__addr))
, _M_addr(_S_wait_addr(__addr, &_M_w._M_ver))
- {
- }
+ { }
+
+ bool
+ _M_laundered() const
+ { return _M_addr == &_M_w._M_ver; }
void
_M_notify(bool __all, bool __bare = false)
{
- if (_M_addr == &_M_w._M_ver)
- __atomic_fetch_add(_M_addr, 1, __ATOMIC_ACQ_REL);
+ if (_M_laundered())
+ {
+ __atomic_fetch_add(_M_addr, 1, __ATOMIC_ACQ_REL);
Please mention this increment in the changelog.
Ugh, sorry, I seem to have forgotten how to read a diff.
OK for trunk and gcc-11 with that change, thanks.
OK to push, no changes needed.
Tested x86_64-pc-linux-gnu, committed to master and cherry-picked to
releases/gcc-11.
