On 05/10/20 15:54 -0700, Thomas Rodgers wrote:
From: Thomas Rodgers <trodg...@redhat.com>
This *should* be the correct patch this time.
There are still some review comments not addressed. I'll keep all my
comments on this version in a single reply, so they aren't lost among
multiple replies.
I think the significant issues like the handling of spurious wakeups
and the missing "no effects" case in _M_try_acquire() are resolved,
thanks.
diff --git a/libstdc++-v3/include/bits/atomic_timed_wait.h
b/libstdc++-v3/include/bits/atomic_timed_wait.h
new file mode 100644
index 00000000000..cd5b6aabc44
--- /dev/null
+++ b/libstdc++-v3/include/bits/atomic_timed_wait.h
[...]
+ struct __timed_waiters : __waiters
+ {
+ template<typename _Clock, typename _Duration>
+ __atomic_wait_status
+ _M_do_wait_until(__platform_wait_t __version,
+ const chrono::time_point<_Clock, _Duration>& __atime)
+ {
+#ifdef _GLIBCXX_HAVE_LINUX_FUTEX
+ return __platform_wait_until(&_M_ver, __version, __atime);
Qualify to prevent ADL in associated namespaces of the _Clock and
_Duration types.
+ template<typename _Tp, typename _Pred,
+ typename _Clock, typename _Duration>
+ bool
+ __atomic_wait_until(const _Tp* __addr, _Tp __old, _Pred __pred,
+ const chrono::time_point<_Clock, _Duration>&
+ __atime) noexcept
+ {
+ using namespace __detail;
+
+ if (std::__atomic_spin(__pred))
+ return true;
+
+ auto& __w = __timed_waiters::_S_timed_for((void*)__addr);
+ auto __version = __w._M_enter_wait();
+ do
+ {
+ __atomic_wait_status __res;
+ if constexpr (__platform_wait_uses_type<_Tp>)
+ {
+ __res = __platform_wait_until((__platform_wait_t*)(void*) __addr,
Qualify to prevent ADL.
diff --git a/libstdc++-v3/include/bits/atomic_wait.h
b/libstdc++-v3/include/bits/atomic_wait.h
new file mode 100644
index 00000000000..30f682e828a
--- /dev/null
+++ b/libstdc++-v3/include/bits/atomic_wait.h
+ template<typename _Tp, typename _Pred>
+ void
+ __atomic_wait(const _Tp* __addr, _Tp __old, _Pred __pred) noexcept
+ {
+ using namespace __detail;
+ if (__atomic_spin(__pred))
Qualify to prevent ADL.
diff --git a/libstdc++-v3/include/bits/semaphore_base.h
b/libstdc++-v3/include/bits/semaphore_base.h
new file mode 100644
index 00000000000..a32a6b12a1b
--- /dev/null
+++ b/libstdc++-v3/include/bits/semaphore_base.h
@@ -0,0 +1,298 @@
+// -*- C++ -*- header.
+
+// Copyright (C) 2020 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.
+
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
+// <http://www.gnu.org/licenses/>.
+
+/** @file bits/semaphore_base.h
+ * This is an internal header file, included by other library headers.
+ * Do not attempt to use it directly. @headername{semaphore}
+ */
+
+#ifndef _GLIBCXX_SEMAPHORE_BASE_H
+#define _GLIBCXX_SEMAPHORE_BASE_H 1
+
+#pragma GCC system_header
+
+#include <bits/c++config.h>
+#include <bits/atomic_base.h>
+#include <bits/atomic_timed_wait.h>
+
+#include <ext/numeric_traits.h>
+
+#if __has_include(<semaphore.h>)
+#define _GLIBCXX_HAVE_POSIX_SEMAPHORE 1
+#include <semaphore.h>
+#endif
+
+#include <chrono>
+#include <type_traits>
+
+#include <iostream>
This shouldn't be here.
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+#ifdef _GLIBCXX_HAVE_POSIX_SEMAPHORE
+ struct __platform_semaphore
+ {
+ using __clock_t = chrono::system_clock;
+ static constexpr ptrdiff_t _S_max = SEM_VALUE_MAX;
+
+ explicit __platform_semaphore(ptrdiff_t __count) noexcept
+ {
+ sem_init(&_M_semaphore, 0, __count);
+ }
+
+ __platform_semaphore(const __platform_semaphore&) = delete;
+ __platform_semaphore& operator=(const __platform_semaphore&) = delete;
+
+ ~__platform_semaphore()
+ { sem_destroy(&_M_semaphore); }
+
+ _GLIBCXX_ALWAYS_INLINE void
+ _M_acquire() noexcept
+ {
+ for (;;)
+ {
+ auto __err = sem_wait(&_M_semaphore);
+ if (__err && (errno == EINTR))
+ continue;
+ else if (__err)
+ std::terminate();
+ else
+ break;
+ }
+ }
+
+ _GLIBCXX_ALWAYS_INLINE void
+ _M_release(std::ptrdiff_t __update) noexcept
+ {
+ for(; __update != 0; --__update)
+ {
+ auto __err = sem_post(&_M_semaphore);
+ if (__err)
+ std::terminate();
+ }
+ }
+
+ bool
+ _M_try_acquire_until_impl(const chrono::time_point<__clock_t>& __atime)
+ noexcept
+ {
+
+ auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
+ auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s);
+
+ struct timespec __ts =
+ {
+ static_cast<std::time_t>(__s.time_since_epoch().count()),
+ static_cast<long>(__ns.count())
+ };
+
+ for (;;)
+ {
+ auto __err = sem_timedwait(&_M_semaphore, &__ts);
+ if (__err && (errno == EINTR))
+ continue;
+ else if (__err && (errno == ETIMEDOUT))
+ return false;
+ else if (__err && (errno == EINVAL))
+ return false; // caller supplied an invalid __atime
+ else if (__err)
+ std::terminate();
+ else
+ break;
It looks like this would be simpler with just one check for __err:
auto __err = sem_timedwait(&_M_semaphore, &__ts);
if (__err)
{
if (errno == EINTR)
continue;
if (errno == ETIMEDOUT || errno == EINVAL)
return false;
else
std::terminate();
}
else
break;
Hopefully the compiler wouldn't actually keep testing __err but I think
it reads better this way anyway.
+ }
+ return true;
+ }
+
+ template<typename _Clock, typename _Duration>
+ bool
+ _M_try_acquire_until(const chrono::time_point<_Clock,
+ _Duration>& __atime) noexcept
+ {
+ if constexpr (std::is_same<__clock_t, _Clock>::value)
is_same_v (it's not just stylistic, the variable template is faster to
compile than the class template).
+ {
+ return _M_try_acquire_until_impl(__atime);
+ }
+ else
+ {
+ const typename _Clock::time_point __c_entry = _Clock::now();
+ const __clock_t __s_entry = __clock_t::now();
+ const auto __delta = __atime - __c_entry;
+ const auto __s_atime = __s_entry + __delta;
+ if (_M_try_acquire_until_impl(__s_atime))
+ return true;
+
+ // We got a timeout when measured against __clock_t but
+ // we need to check against the caller-supplied clock
+ // to tell whether we should return a timeout.
+ return (_Clock::now() < __atime);
+ }
+ }
+
+ template<typename _Rep, typename _Period>
+ _GLIBCXX_ALWAYS_INLINE bool
+ _M_try_acquire_for(const chrono::duration<_Rep, _Period>& __rtime)
+ noexcept
+ { return _M_try_acquire_until(__clock_t::now() + __rtime); }
+
+ private:
+ sem_t _M_semaphore;
+ };
+#endif // _GLIBCXX_HAVE_POSIX_SEMAPHORE
+
+ template<typename _Tp>
+ struct __atomic_semaphore
+ {
+ static_assert(std::is_integral_v<_Tp>);
+ static_assert(__gnu_cxx::__int_traits<_Tp>::__max
+ <= __gnu_cxx::__int_traits<ptrdiff_t>::__max);
+ static constexpr ptrdiff_t _S_max = __gnu_cxx::__int_traits<_Tp>::__max;
+
+ explicit __atomic_semaphore(_Tp __count) noexcept
+ : _M_counter(__count)
+ {
+ __glibcxx_assert(__count >= 0 && __count <= _S_max);
+ }
+
+ __atomic_semaphore(const __atomic_semaphore&) = delete;
+ __atomic_semaphore& operator=(const __atomic_semaphore&) = delete;
+
+ _GLIBCXX_ALWAYS_INLINE void
+ _M_acquire() noexcept
+ {
+ auto const __pred = [this]
+ {
+ auto __old = __atomic_impl::load(&this->_M_counter,
+ memory_order::acquire);
+ if (__old == 0)
+ return false;
+ return __atomic_impl::compare_exchange_strong(&this->_M_counter,
+ __old, __old - 1,
+ memory_order::acquire,
+ memory_order::release);
+ };
+ auto __old = __atomic_impl::load(&_M_counter, memory_order_relaxed);
+ __atomic_wait(&_M_counter, __old, __pred);
Qualify to prevent ADL.
--- /dev/null
+++ b/libstdc++-v3/include/std/latch
@@ -0,0 +1,91 @@
+// <latch> -*- C++ -*-
+
+// Copyright (C) 2020 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.
+
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
+// <http://www.gnu.org/licenses/>.
+
+/** @file include/latch
+ * This is a Standard C++ Library header.
+ */
+
+#ifndef _GLIBCXX_LATCH
+#define _GLIBCXX_LATCH
+
+#pragma GCC system_header
+
+#if __cplusplus > 201703L
+#define __cpp_lib_latch 201907L
+
+#include <bits/atomic_base.h>
+#include <ext/numeric_traits.h>
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+ class latch
+ {
+ public:
+ static constexpr ptrdiff_t
+ max() noexcept
+ { return __gnu_cxx::__int_traits<ptrdiff_t>::__max; }
+
+ constexpr explicit latch(ptrdiff_t __expected) noexcept
+ : _M_a(__expected) { }
+
+ ~latch() = default;
+ latch(const latch&) = delete;
+ latch& operator=(const latch&) = delete;
+
+ _GLIBCXX_ALWAYS_INLINE void
+ count_down(ptrdiff_t __update = 1)
+ {
+ auto const __old = __atomic_impl::fetch_sub(&_M_a,
+ __update, memory_order::release);
+ if (__old == __update)
+ __atomic_impl::notify_all(&_M_a);
+ }
+
+ _GLIBCXX_ALWAYS_INLINE bool
+ try_wait() const noexcept
+ { return __atomic_impl::load(&_M_a, memory_order::acquire) == 0; }
+
+ _GLIBCXX_ALWAYS_INLINE void
+ wait() const noexcept
+ {
+ auto const __old = __atomic_impl::load(&_M_a, memory_order::acquire);
+ __atomic_wait(&_M_a, __old, [this] { return this->try_wait(); });
Qualify to prevent ADL.
+ }
+
+ _GLIBCXX_ALWAYS_INLINE void
+ arrive_and_wait(ptrdiff_t __update = 1) noexcept
+ {
+ count_down(__update);
+ wait();
+ }
+
+ private:
+ alignas(__alignof__(ptrdiff_t)) ptrdiff_t _M_a;
+ };
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace
+#endif // __cplusplus > 201703L
+#endif // _GLIBCXX_LATCH
