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);
+ __all = true;
+ }
_M_w._M_notify(_M_addr, __all, __bare);
}
@@ -320,7 +327,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_Spin __spin = _Spin{ })
{
auto const __pred = [=]
- { return __detail::__atomic_compare(__old, __vfn()); };
+ { return !__detail::__atomic_compare(__old, __vfn()); };
if constexpr (__platform_wait_uses_type<_Up>)
{
@@ -387,7 +394,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
__platform_wait_t __val;
if (__base_type::_M_do_spin_v(__old, __vfn, __val))
return;
- __base_type::_M_w._M_do_wait(__base_type::_M_addr, __val);
+
+ do
+ {
+ __base_type::_M_w._M_do_wait(__base_type::_M_addr, __val);
+ }
+ while (__detail::__atomic_compare(__old, __vfn()));
}
template<typename _Pred>
@@ -452,7 +464,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
__atomic_notify_address(const _Tp* __addr, bool __all) noexcept
{
__detail::__bare_wait __w(__addr);
- __w._M_notify(__all, true);
+ __w._M_notify(__all);
}
// This call is to be used by atomic types which track contention externally
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/100334.cc
b/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/100334.cc
new file mode 100644
index 00000000000..3e63eca42fa
--- /dev/null
+++ b/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/100334.cc
@@ -0,0 +1,94 @@
+// { dg-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+// { dg-require-gthreads "" }
+// { dg-additional-options "-pthread" { target pthread } }
+// { dg-add-options libatomic }
+
+// Copyright (C) 2021 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <atomic>
+#include <future>
+
+#include <testsuite_hooks.h>
+
+template <typename T>
+struct atomics_sharing_same_waiter
+{
+ std::atomic<T> tmp[49 * 4] = {};
+ std::atomic<T>* a[4] = {
+ { &tmp[0] },
+ { &tmp[16 * 4] },
+ { &tmp[32 * 4] },
+ { &tmp[48 * 4] }
+ };
+};
+
+constexpr unsigned key(void * a)
+{
+ constexpr uintptr_t ct = 16;
+ return (uintptr_t(a) >> 2) % ct;
+}
+
+int
+main()
+{
+ // all atomic share the same waiter
+// atomics_sharing_same_waiter<char> atomics;
+ atomics_sharing_same_waiter<char> atomics;
+ for (auto& atom : atomics.a)
+ {
+ atom->store(0);
+ }
+
+ auto a = &std::__detail::__waiter_pool_base::_S_for(reinterpret_cast<char
*>(atomics.a[0]));
+ auto b = &std::__detail::__waiter_pool_base::_S_for(reinterpret_cast<char
*>(atomics.a[1]));
+ VERIFY( a == b );
+
+ auto fut0 = std::async(std::launch::async, [&] { atomics.a[0]->wait(0); });
+ auto fut1 = std::async(std::launch::async, [&] { atomics.a[1]->wait(0); });
+ auto fut2 = std::async(std::launch::async, [&] { atomics.a[2]->wait(0); });
+ auto fut3 = std::async(std::launch::async, [&] { atomics.a[3]->wait(0); });
+
+ // make sure the all threads already await
+ std::this_thread::sleep_for(std::chrono::milliseconds{100});
+
+ atomics.a[2]->store(1);
+ atomics.a[2]->notify_one();
+
+ VERIFY(std::future_status::timeout ==
fut0.wait_for(std::chrono::milliseconds{100}));
+ VERIFY(atomics.a[0]->load() == 0);
+
+ VERIFY(std::future_status::timeout ==
fut1.wait_for(std::chrono::milliseconds{100}));
+ VERIFY(atomics.a[1]->load() == 0);
+
+ VERIFY(std::future_status::ready ==
fut2.wait_for(std::chrono::milliseconds{100}));
+ VERIFY(atomics.a[2]->load() == 1);
+
+ VERIFY(std::future_status::timeout ==
fut3.wait_for(std::chrono::milliseconds{100}));
+ VERIFY(atomics.a[3]->load() == 0);
+
+ atomics.a[0]->store(1);
+ atomics.a[0]->notify_one();
+ atomics.a[1]->store(1);
+ atomics.a[1]->notify_one();
+ atomics.a[3]->store(1);
+ atomics.a[3]->notify_one();
+
+ return 0;
+}
+
--
2.30.2
