| // -*- C++ -*- |
| //===----------------------------------------------------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef _LIBCPP_SEMAPHORE |
| #define _LIBCPP_SEMAPHORE |
| |
| /* |
| semaphore synopsis |
| |
| namespace std { |
| |
| template<ptrdiff_t least_max_value = implementation-defined> |
| class counting_semaphore // since C++20 |
| { |
| public: |
| static constexpr ptrdiff_t max() noexcept; |
| |
| constexpr explicit counting_semaphore(ptrdiff_t desired); |
| ~counting_semaphore(); |
| |
| counting_semaphore(const counting_semaphore&) = delete; |
| counting_semaphore& operator=(const counting_semaphore&) = delete; |
| |
| void release(ptrdiff_t update = 1); |
| void acquire(); |
| bool try_acquire() noexcept; |
| template<class Rep, class Period> |
| bool try_acquire_for(const chrono::duration<Rep, Period>& rel_time); |
| template<class Clock, class Duration> |
| bool try_acquire_until(const chrono::time_point<Clock, Duration>& abs_time); |
| |
| private: |
| ptrdiff_t counter; // exposition only |
| }; |
| |
| using binary_semaphore = counting_semaphore<1>; // since C++20 |
| |
| } |
| |
| */ |
| |
| #include <__config> |
| |
| #if !defined(_LIBCPP_HAS_NO_THREADS) |
| |
| # include <__assert> |
| # include <__atomic/atomic_base.h> |
| # include <__atomic/atomic_sync.h> |
| # include <__atomic/memory_order.h> |
| # include <__chrono/time_point.h> |
| # include <__thread/poll_with_backoff.h> |
| # include <__thread/support.h> |
| # include <__thread/timed_backoff_policy.h> |
| # include <cstddef> |
| # include <limits> |
| # include <version> |
| |
| # if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) |
| # pragma GCC system_header |
| # endif |
| |
| _LIBCPP_PUSH_MACROS |
| # include <__undef_macros> |
| |
| # if _LIBCPP_STD_VER >= 20 |
| |
| _LIBCPP_BEGIN_NAMESPACE_STD |
| |
| /* |
| |
| __atomic_semaphore_base is the general-case implementation. |
| It is a typical Dijkstra semaphore algorithm over atomics, wait and notify |
| functions. It avoids contention against users' own use of those facilities. |
| |
| */ |
| |
| # define _LIBCPP_SEMAPHORE_MAX (numeric_limits<ptrdiff_t>::max()) |
| |
| class __atomic_semaphore_base { |
| __atomic_base<ptrdiff_t> __a_; |
| |
| public: |
| _LIBCPP_HIDE_FROM_ABI constexpr explicit __atomic_semaphore_base(ptrdiff_t __count) : __a_(__count) {} |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void release(ptrdiff_t __update = 1) { |
| auto __old = __a_.fetch_add(__update, memory_order_release); |
| _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN( |
| __update <= _LIBCPP_SEMAPHORE_MAX - __old, "update is greater than the expected value"); |
| if (__old == 0) { |
| __a_.notify_all(); |
| } |
| } |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void acquire() { |
| std::__atomic_wait_unless( |
| __a_, [this](ptrdiff_t& __old) { return __try_acquire_impl(__old); }, memory_order_relaxed); |
| } |
| template <class _Rep, class _Period> |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI bool |
| try_acquire_for(chrono::duration<_Rep, _Period> const& __rel_time) { |
| if (__rel_time == chrono::duration<_Rep, _Period>::zero()) |
| return try_acquire(); |
| auto const __poll_fn = [this]() { return try_acquire(); }; |
| return std::__libcpp_thread_poll_with_backoff(__poll_fn, __libcpp_timed_backoff_policy(), __rel_time); |
| } |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI bool try_acquire() { |
| auto __old = __a_.load(memory_order_relaxed); |
| return __try_acquire_impl(__old); |
| } |
| |
| private: |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI bool __try_acquire_impl(ptrdiff_t& __old) { |
| while (true) { |
| if (__old == 0) |
| return false; |
| if (__a_.compare_exchange_weak(__old, __old - 1, memory_order_acquire, memory_order_relaxed)) |
| return true; |
| } |
| } |
| }; |
| |
| template <ptrdiff_t __least_max_value = _LIBCPP_SEMAPHORE_MAX> |
| class counting_semaphore { |
| __atomic_semaphore_base __semaphore_; |
| |
| public: |
| static_assert(__least_max_value >= 0, "The least maximum value must be a positive number"); |
| |
| static constexpr ptrdiff_t max() noexcept { return __least_max_value; } |
| |
| _LIBCPP_HIDE_FROM_ABI constexpr explicit counting_semaphore(ptrdiff_t __count) : __semaphore_(__count) { |
| _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN( |
| __count >= 0, |
| "counting_semaphore::counting_semaphore(ptrdiff_t): counting_semaphore cannot be " |
| "initialized with a negative value"); |
| _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN( |
| __count <= max(), |
| "counting_semaphore::counting_semaphore(ptrdiff_t): counting_semaphore cannot be " |
| "initialized with a value greater than max()"); |
| } |
| ~counting_semaphore() = default; |
| |
| counting_semaphore(const counting_semaphore&) = delete; |
| counting_semaphore& operator=(const counting_semaphore&) = delete; |
| |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void release(ptrdiff_t __update = 1) { |
| _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(__update >= 0, "counting_semaphore:release called with a negative value"); |
| __semaphore_.release(__update); |
| } |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void acquire() { __semaphore_.acquire(); } |
| template <class _Rep, class _Period> |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI bool |
| try_acquire_for(chrono::duration<_Rep, _Period> const& __rel_time) { |
| return __semaphore_.try_acquire_for(chrono::duration_cast<chrono::nanoseconds>(__rel_time)); |
| } |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI bool try_acquire() { return __semaphore_.try_acquire(); } |
| template <class _Clock, class _Duration> |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI bool |
| try_acquire_until(chrono::time_point<_Clock, _Duration> const& __abs_time) { |
| auto const __current = _Clock::now(); |
| if (__current >= __abs_time) |
| return try_acquire(); |
| else |
| return try_acquire_for(__abs_time - __current); |
| } |
| }; |
| |
| using binary_semaphore = counting_semaphore<1>; |
| |
| _LIBCPP_END_NAMESPACE_STD |
| |
| # endif // _LIBCPP_STD_VER >= 20 |
| |
| _LIBCPP_POP_MACROS |
| |
| #endif // !defined(_LIBCPP_HAS_NO_THREADS) |
| |
| #if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20 |
| # include <atomic> |
| #endif |
| |
| #endif // _LIBCPP_SEMAPHORE |