| // -*- C++ -*- |
| //===--------------------------- latch -----------------------------------===// |
| // |
| // 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_LATCH |
| #define _LIBCPP_LATCH |
| |
| /* |
| latch synopsis |
| |
| namespace std |
| { |
| |
| class latch |
| { |
| public: |
| constexpr explicit latch(ptrdiff_t __expected); |
| ~latch(); |
| |
| latch(const latch&) = delete; |
| latch& operator=(const latch&) = delete; |
| |
| void count_down(ptrdiff_t __update = 1); |
| bool try_wait() const noexcept; |
| void wait() const; |
| void arrive_and_wait(ptrdiff_t __update = 1); |
| |
| private: |
| ptrdiff_t __counter; // exposition only |
| }; |
| |
| } |
| |
| */ |
| |
| #include <__config> |
| #include <atomic> |
| |
| #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) |
| #pragma GCC system_header |
| #endif |
| |
| #ifdef _LIBCPP_HAS_NO_THREADS |
| # error <latch> is not supported on this single threaded system |
| #endif |
| |
| #if _LIBCPP_STD_VER >= 14 |
| |
| _LIBCPP_BEGIN_NAMESPACE_STD |
| |
| class latch |
| { |
| __atomic_base<ptrdiff_t> __a; |
| |
| public: |
| static constexpr ptrdiff_t max() noexcept { |
| return numeric_limits<ptrdiff_t>::max(); |
| } |
| |
| inline _LIBCPP_INLINE_VISIBILITY |
| constexpr explicit latch(ptrdiff_t __expected) : __a(__expected) { } |
| |
| ~latch() = default; |
| latch(const latch&) = delete; |
| latch& operator=(const latch&) = delete; |
| |
| inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY |
| void count_down(ptrdiff_t __update = 1) |
| { |
| auto const __old = __a.fetch_sub(__update, memory_order_release); |
| if(__old == __update) |
| __a.notify_all(); |
| } |
| inline _LIBCPP_INLINE_VISIBILITY |
| bool try_wait() const noexcept |
| { |
| return 0 == __a.load(memory_order_acquire); |
| } |
| inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY |
| void wait() const |
| { |
| auto const __test_fn = [=]() -> bool { |
| return try_wait(); |
| }; |
| __cxx_atomic_wait(&__a.__a_, __test_fn); |
| } |
| inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY |
| void arrive_and_wait(ptrdiff_t __update = 1) |
| { |
| count_down(__update); |
| wait(); |
| } |
| }; |
| |
| _LIBCPP_END_NAMESPACE_STD |
| |
| #endif // _LIBCPP_STD_VER >= 14 |
| |
| #endif //_LIBCPP_LATCH |