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// -*- C++ -*- header. |
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|
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// Copyright (C) 2020-2021 Free Software Foundation, Inc. |
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// |
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// This file is part of the GNU ISO C++ Library. This library is free |
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// software; you can redistribute it and/or modify it under the |
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// terms of the GNU General Public License as published by the |
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// Free Software Foundation; either version 3, or (at your option) |
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// any later version. |
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|
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// This library is distributed in the hope that it will be useful, |
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// but WITHOUT ANY WARRANTY; without even the implied warranty of |
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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// GNU General Public License for more details. |
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|
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// Under Section 7 of GPL version 3, you are granted additional |
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// permissions described in the GCC Runtime Library Exception, version |
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// 3.1, as published by the Free Software Foundation. |
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|
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// You should have received a copy of the GNU General Public License and |
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// a copy of the GCC Runtime Library Exception along with this program; |
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// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see |
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// <http://www.gnu.org/licenses/>. |
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|
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/** @file bits/semaphore_base.h |
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* This is an internal header file, included by other library headers. |
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* Do not attempt to use it directly. @headername{semaphore} |
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*/ |
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|
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#ifndef _GLIBCXX_SEMAPHORE_BASE_H |
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#define _GLIBCXX_SEMAPHORE_BASE_H 1 |
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|
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#pragma GCC system_header |
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|
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#include <bits/atomic_base.h> |
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#if __cpp_lib_atomic_wait |
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#include <bits/atomic_timed_wait.h> |
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#include <ext/numeric_traits.h> |
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#endif // __cpp_lib_atomic_wait |
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|
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#ifdef _GLIBCXX_HAVE_POSIX_SEMAPHORE |
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# include <limits.h> |
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# include <semaphore.h> |
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#endif |
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|
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#include <chrono> |
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#include <type_traits> |
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|
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namespace std _GLIBCXX_VISIBILITY(default) |
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{ |
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_GLIBCXX_BEGIN_NAMESPACE_VERSION |
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|
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#ifdef _GLIBCXX_HAVE_POSIX_SEMAPHORE |
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struct __platform_semaphore |
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{ |
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using __clock_t = chrono::system_clock; |
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#ifdef SEM_VALUE_MAX |
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static constexpr ptrdiff_t _S_max = SEM_VALUE_MAX; |
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#else |
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static constexpr ptrdiff_t _S_max = _POSIX_SEM_VALUE_MAX; |
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#endif |
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|
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explicit __platform_semaphore(ptrdiff_t __count) noexcept |
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{ |
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sem_init(&_M_semaphore, 0, __count); |
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} |
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|
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__platform_semaphore(const __platform_semaphore&) = delete; |
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__platform_semaphore& operator=(const __platform_semaphore&) = delete; |
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|
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~__platform_semaphore() |
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{ sem_destroy(&_M_semaphore); } |
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|
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_GLIBCXX_ALWAYS_INLINE void |
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_M_acquire() noexcept |
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{ |
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for (;;) |
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{ |
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auto __err = sem_wait(&_M_semaphore); |
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if (__err && (errno == EINTR)) |
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continue; |
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else if (__err) |
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std::terminate(); |
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else |
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break; |
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} |
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} |
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|
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_GLIBCXX_ALWAYS_INLINE bool |
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_M_try_acquire() noexcept |
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{ |
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for (;;) |
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{ |
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auto __err = sem_trywait(&_M_semaphore); |
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if (__err && (errno == EINTR)) |
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continue; |
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else if (__err && (errno == EAGAIN)) |
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return false; |
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else if (__err) |
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std::terminate(); |
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else |
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break; |
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} |
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return true; |
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} |
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|
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_GLIBCXX_ALWAYS_INLINE void |
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_M_release(std::ptrdiff_t __update) noexcept |
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{ |
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for(; __update != 0; --__update) |
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{ |
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auto __err = sem_post(&_M_semaphore); |
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if (__err) |
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std::terminate(); |
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} |
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} |
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|
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bool |
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_M_try_acquire_until_impl(const chrono::time_point<__clock_t>& __atime) |
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noexcept |
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{ |
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|
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auto __s = chrono::time_point_cast<chrono::seconds>(__atime); |
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auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s); |
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|
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struct timespec __ts = |
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{ |
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static_cast<std::time_t>(__s.time_since_epoch().count()), |
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static_cast<long>(__ns.count()) |
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}; |
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|
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for (;;) |
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{ |
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if (auto __err = sem_timedwait(&_M_semaphore, &__ts)) |
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{ |
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if (errno == EINTR) |
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continue; |
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else if (errno == ETIMEDOUT || errno == EINVAL) |
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return false; |
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else |
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std::terminate(); |
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} |
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else |
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break; |
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} |
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return true; |
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} |
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|
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template<typename _Clock, typename _Duration> |
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bool |
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_M_try_acquire_until(const chrono::time_point<_Clock, |
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_Duration>& __atime) noexcept |
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{ |
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if constexpr (std::is_same_v<__clock_t, _Clock>) |
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{ |
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return _M_try_acquire_until_impl(__atime); |
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} |
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else |
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{ |
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const typename _Clock::time_point __c_entry = _Clock::now(); |
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const auto __s_entry = __clock_t::now(); |
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const auto __delta = __atime - __c_entry; |
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const auto __s_atime = __s_entry + __delta; |
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if (_M_try_acquire_until_impl(__s_atime)) |
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return true; |
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|
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// We got a timeout when measured against __clock_t but |
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// we need to check against the caller-supplied clock |
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// to tell whether we should return a timeout. |
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return (_Clock::now() < __atime); |
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} |
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} |
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|
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template<typename _Rep, typename _Period> |
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_GLIBCXX_ALWAYS_INLINE bool |
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_M_try_acquire_for(const chrono::duration<_Rep, _Period>& __rtime) |
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noexcept |
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{ return _M_try_acquire_until(__clock_t::now() + __rtime); } |
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|
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private: |
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sem_t _M_semaphore; |
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}; |
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#endif // _GLIBCXX_HAVE_POSIX_SEMAPHORE |
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|
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#if __cpp_lib_atomic_wait |
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struct __atomic_semaphore |
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{ |
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static constexpr ptrdiff_t _S_max = __gnu_cxx::__int_traits<int>::__max; |
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explicit __atomic_semaphore(__detail::__platform_wait_t __count) noexcept |
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: _M_counter(__count) |
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{ |
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__glibcxx_assert(__count >= 0 && __count <= _S_max); |
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} |
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|
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__atomic_semaphore(const __atomic_semaphore&) = delete; |
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__atomic_semaphore& operator=(const __atomic_semaphore&) = delete; |
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|
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static _GLIBCXX_ALWAYS_INLINE bool |
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_S_do_try_acquire(__detail::__platform_wait_t* __counter) noexcept |
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{ |
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auto __old = __atomic_impl::load(__counter, memory_order::acquire); |
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if (__old == 0) |
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return false; |
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|
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return __atomic_impl::compare_exchange_strong(__counter, |
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__old, __old - 1, |
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memory_order::acquire, |
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memory_order::relaxed); |
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} |
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|
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_GLIBCXX_ALWAYS_INLINE void |
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_M_acquire() noexcept |
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{ |
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auto const __pred = |
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[this] { return _S_do_try_acquire(&this->_M_counter); }; |
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std::__atomic_wait_address_bare(&_M_counter, __pred); |
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} |
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|
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bool |
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_M_try_acquire() noexcept |
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{ |
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auto const __pred = |
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[this] { return _S_do_try_acquire(&this->_M_counter); }; |
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return std::__detail::__atomic_spin(__pred); |
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} |
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|
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template<typename _Clock, typename _Duration> |
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_GLIBCXX_ALWAYS_INLINE bool |
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_M_try_acquire_until(const chrono::time_point<_Clock, |
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_Duration>& __atime) noexcept |
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{ |
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auto const __pred = |
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[this] { return _S_do_try_acquire(&this->_M_counter); }; |
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|
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return __atomic_wait_address_until_bare(&_M_counter, __pred, __atime); |
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} |
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|
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template<typename _Rep, typename _Period> |
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_GLIBCXX_ALWAYS_INLINE bool |
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_M_try_acquire_for(const chrono::duration<_Rep, _Period>& __rtime) |
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noexcept |
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{ |
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auto const __pred = |
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[this] { return _S_do_try_acquire(&this->_M_counter); }; |
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|
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return __atomic_wait_address_for_bare(&_M_counter, __pred, __rtime); |
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} |
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|
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_GLIBCXX_ALWAYS_INLINE void |
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_M_release(ptrdiff_t __update) noexcept |
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{ |
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if (0 < __atomic_impl::fetch_add(&_M_counter, __update, memory_order_release)) |
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return; |
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if (__update > 1) |
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__atomic_notify_address_bare(&_M_counter, true); |
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else |
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__atomic_notify_address_bare(&_M_counter, true); |
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// FIXME - Figure out why this does not wake a waiting thread |
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// __atomic_notify_address_bare(&_M_counter, false); |
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} |
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|
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private: |
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alignas(__detail::__platform_wait_alignment) |
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__detail::__platform_wait_t _M_counter; |
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}; |
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#endif // __cpp_lib_atomic_wait |
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|
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// Note: the _GLIBCXX_USE_POSIX_SEMAPHORE macro can be used to force the |
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// use of Posix semaphores (sem_t). Doing so however, alters the ABI. |
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#if defined __cpp_lib_atomic_wait && !_GLIBCXX_USE_POSIX_SEMAPHORE |
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using __semaphore_impl = __atomic_semaphore; |
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#elif _GLIBCXX_HAVE_POSIX_SEMAPHORE |
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using __semaphore_impl = __platform_semaphore; |
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#endif |
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|
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_GLIBCXX_END_NAMESPACE_VERSION |
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} // namespace std |
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#endif // _GLIBCXX_SEMAPHORE_BASE_H |
