| // -*- 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 |
| { |
| 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>; |
| |
| } |
| |
| */ |
| |
| #include <__availability> |
| #include <__config> |
| #include <__threading_support> |
| #include <atomic> |
| |
| #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) |
| #pragma GCC system_header |
| #endif |
| |
| #ifdef _LIBCPP_HAS_NO_THREADS |
| # error <semaphore> is not supported on this single threaded system |
| #endif |
| |
| _LIBCPP_PUSH_MACROS |
| #include <__undef_macros> |
| |
| #if _LIBCPP_STD_VER >= 14 |
| |
| _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. |
| |
| */ |
| |
| class __atomic_semaphore_base |
| { |
| __atomic_base<ptrdiff_t> __a; |
| |
| public: |
| _LIBCPP_INLINE_VISIBILITY |
| constexpr explicit __atomic_semaphore_base(ptrdiff_t __count) : __a(__count) |
| { |
| } |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY |
| void release(ptrdiff_t __update = 1) |
| { |
| if(0 < __a.fetch_add(__update, memory_order_release)) |
| ; |
| else if(__update > 1) |
| __a.notify_all(); |
| else |
| __a.notify_one(); |
| } |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY |
| void acquire() |
| { |
| auto const __test_fn = [this]() -> bool { |
| auto __old = __a.load(memory_order_relaxed); |
| return (__old != 0) && __a.compare_exchange_strong(__old, __old - 1, memory_order_acquire, memory_order_relaxed); |
| }; |
| __cxx_atomic_wait(&__a.__a_, __test_fn); |
| } |
| template <class Rep, class Period> |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY |
| bool try_acquire_for(chrono::duration<Rep, Period> const& __rel_time) |
| { |
| if (__rel_time == chrono::duration<Rep, Period>::zero()) |
| return try_acquire(); |
| auto const __test_fn = [this]() { return try_acquire(); }; |
| return __libcpp_thread_poll_with_backoff(__test_fn, __libcpp_timed_backoff_policy(), __rel_time); |
| } |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY |
| bool try_acquire() |
| { |
| auto __old = __a.load(memory_order_acquire); |
| while (true) { |
| if (__old == 0) |
| return false; |
| if (__a.compare_exchange_strong(__old, __old - 1, memory_order_acquire, memory_order_relaxed)) |
| return true; |
| } |
| } |
| }; |
| |
| #define _LIBCPP_SEMAPHORE_MAX (numeric_limits<ptrdiff_t>::max()) |
| |
| template<ptrdiff_t __least_max_value = _LIBCPP_SEMAPHORE_MAX> |
| class counting_semaphore |
| { |
| __atomic_semaphore_base __semaphore; |
| |
| public: |
| static constexpr ptrdiff_t max() noexcept { |
| return __least_max_value; |
| } |
| |
| _LIBCPP_INLINE_VISIBILITY |
| constexpr explicit counting_semaphore(ptrdiff_t __count) : __semaphore(__count) { } |
| ~counting_semaphore() = default; |
| |
| counting_semaphore(const counting_semaphore&) = delete; |
| counting_semaphore& operator=(const counting_semaphore&) = delete; |
| |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY |
| void release(ptrdiff_t __update = 1) |
| { |
| __semaphore.release(__update); |
| } |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY |
| void acquire() |
| { |
| __semaphore.acquire(); |
| } |
| template<class Rep, class Period> |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY |
| 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_INLINE_VISIBILITY |
| bool try_acquire() |
| { |
| return __semaphore.try_acquire(); |
| } |
| template <class Clock, class Duration> |
| _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY |
| 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 >= 14 |
| |
| _LIBCPP_POP_MACROS |
| |
| #endif //_LIBCPP_SEMAPHORE |