semaphore_base.h
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// -*- C++ -*- header.
// Copyright (C) 2020-2021 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.
// 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/atomic_base.h>
#if __cpp_lib_atomic_wait
#include <bits/atomic_timed_wait.h>
#include <ext/numeric_traits.h>
#endif // __cpp_lib_atomic_wait
#ifdef _GLIBCXX_HAVE_POSIX_SEMAPHORE
# include <exception> // std::terminate
# include <cerrno> // errno, EINTR, EAGAIN etc.
# include <limits.h> // SEM_VALUE_MAX
# include <semaphore.h> // sem_t, sem_init, sem_wait, sem_post etc.
#endif
#include <chrono>
#include <type_traits>
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
#ifdef _GLIBCXX_HAVE_POSIX_SEMAPHORE
struct __platform_semaphore
{
using __clock_t = chrono::system_clock;
#ifdef SEM_VALUE_MAX
static constexpr ptrdiff_t _S_max = SEM_VALUE_MAX;
#else
static constexpr ptrdiff_t _S_max = _POSIX_SEM_VALUE_MAX;
#endif
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 bool
_M_try_acquire() noexcept
{
for (;;)
{
auto __err = sem_trywait(&_M_semaphore);
if (__err && (errno == EINTR))
continue;
else if (__err && (errno == EAGAIN))
return false;
else if (__err)
std::terminate();
else
break;
}
return true;
}
_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 (;;)
{
if (auto __err = sem_timedwait(&_M_semaphore, &__ts))
{
if (errno == EINTR)
continue;
else if (errno == ETIMEDOUT || errno == EINVAL)
return false;
else
std::terminate();
}
else
break;
}
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_v<__clock_t, _Clock>)
{
return _M_try_acquire_until_impl(__atime);
}
else
{
const typename _Clock::time_point __c_entry = _Clock::now();
const auto __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
#if __cpp_lib_atomic_wait
struct __atomic_semaphore
{
static constexpr ptrdiff_t _S_max = __gnu_cxx::__int_traits<int>::__max;
explicit __atomic_semaphore(__detail::__platform_wait_t __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;
static _GLIBCXX_ALWAYS_INLINE bool
_S_do_try_acquire(__detail::__platform_wait_t* __counter) noexcept
{
auto __old = __atomic_impl::load(__counter, memory_order::acquire);
if (__old == 0)
return false;
return __atomic_impl::compare_exchange_strong(__counter,
__old, __old - 1,
memory_order::acquire,
memory_order::relaxed);
}
_GLIBCXX_ALWAYS_INLINE void
_M_acquire() noexcept
{
auto const __pred =
[this] { return _S_do_try_acquire(&this->_M_counter); };
std::__atomic_wait_address_bare(&_M_counter, __pred);
}
bool
_M_try_acquire() noexcept
{
auto const __pred =
[this] { return _S_do_try_acquire(&this->_M_counter); };
return std::__detail::__atomic_spin(__pred);
}
template<typename _Clock, typename _Duration>
_GLIBCXX_ALWAYS_INLINE bool
_M_try_acquire_until(const chrono::time_point<_Clock,
_Duration>& __atime) noexcept
{
auto const __pred =
[this] { return _S_do_try_acquire(&this->_M_counter); };
return __atomic_wait_address_until_bare(&_M_counter, __pred, __atime);
}
template<typename _Rep, typename _Period>
_GLIBCXX_ALWAYS_INLINE bool
_M_try_acquire_for(const chrono::duration<_Rep, _Period>& __rtime)
noexcept
{
auto const __pred =
[this] { return _S_do_try_acquire(&this->_M_counter); };
return __atomic_wait_address_for_bare(&_M_counter, __pred, __rtime);
}
_GLIBCXX_ALWAYS_INLINE void
_M_release(ptrdiff_t __update) noexcept
{
if (0 < __atomic_impl::fetch_add(&_M_counter, __update, memory_order_release))
return;
if (__update > 1)
__atomic_notify_address_bare(&_M_counter, true);
else
__atomic_notify_address_bare(&_M_counter, true);
// FIXME - Figure out why this does not wake a waiting thread
// __atomic_notify_address_bare(&_M_counter, false);
}
private:
alignas(__detail::__platform_wait_alignment)
__detail::__platform_wait_t _M_counter;
};
#endif // __cpp_lib_atomic_wait
// Note: the _GLIBCXX_USE_POSIX_SEMAPHORE macro can be used to force the
// use of Posix semaphores (sem_t). Doing so however, alters the ABI.
#if defined __cpp_lib_atomic_wait && !_GLIBCXX_USE_POSIX_SEMAPHORE
using __semaphore_impl = __atomic_semaphore;
#elif _GLIBCXX_HAVE_POSIX_SEMAPHORE
using __semaphore_impl = __platform_semaphore;
#endif
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // _GLIBCXX_SEMAPHORE_BASE_H
exception
cerrno
atomic_base.h
atomic_timed_wait.h
std::terminate
void terminate() noexcept
std
ISO C++ entities toplevel namespace is std.
__gnu_cxx::__int_traits
__numeric_traits_integer< _Tp > __int_traits
Convenience alias for __numeric_traits<integer-type>.
Definition: ext/numeric_traits.h:136
chrono
numeric_traits.h
type_traits