1// -*- C++ -*- 2//===----------------------------------------------------------------------===// 3// 4// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 5// See https://llvm.org/LICENSE.txt for license information. 6// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 7// 8//===----------------------------------------------------------------------===// 9 10#ifndef _LIBCPP_LATCH 11#define _LIBCPP_LATCH 12 13/* 14 latch synopsis 15 16namespace std 17{ 18 19 class latch 20 { 21 public: 22 static constexpr ptrdiff_t max() noexcept; 23 24 constexpr explicit latch(ptrdiff_t __expected); 25 ~latch(); 26 27 latch(const latch&) = delete; 28 latch& operator=(const latch&) = delete; 29 30 void count_down(ptrdiff_t __update = 1); 31 bool try_wait() const noexcept; 32 void wait() const; 33 void arrive_and_wait(ptrdiff_t __update = 1); 34 35 private: 36 ptrdiff_t __counter; // exposition only 37 }; 38 39} 40 41*/ 42 43#include <__availability> 44#include <__config> 45#include <atomic> 46#include <version> 47 48#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 49#pragma GCC system_header 50#endif 51 52#ifdef _LIBCPP_HAS_NO_THREADS 53# error <latch> is not supported on this single threaded system 54#endif 55 56_LIBCPP_PUSH_MACROS 57#include <__undef_macros> 58 59#if _LIBCPP_STD_VER >= 14 60 61_LIBCPP_BEGIN_NAMESPACE_STD 62 63class latch 64{ 65 __atomic_base<ptrdiff_t> __a; 66 67public: 68 static constexpr ptrdiff_t max() noexcept { 69 return numeric_limits<ptrdiff_t>::max(); 70 } 71 72 inline _LIBCPP_INLINE_VISIBILITY 73 constexpr explicit latch(ptrdiff_t __expected) : __a(__expected) { } 74 75 ~latch() = default; 76 latch(const latch&) = delete; 77 latch& operator=(const latch&) = delete; 78 79 inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY 80 void count_down(ptrdiff_t __update = 1) 81 { 82 auto const __old = __a.fetch_sub(__update, memory_order_release); 83 if(__old == __update) 84 __a.notify_all(); 85 } 86 inline _LIBCPP_INLINE_VISIBILITY 87 bool try_wait() const noexcept 88 { 89 return 0 == __a.load(memory_order_acquire); 90 } 91 inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY 92 void wait() const 93 { 94 auto const __test_fn = [=]() -> bool { 95 return try_wait(); 96 }; 97 __cxx_atomic_wait(&__a.__a_, __test_fn); 98 } 99 inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY 100 void arrive_and_wait(ptrdiff_t __update = 1) 101 { 102 count_down(__update); 103 wait(); 104 } 105}; 106 107_LIBCPP_END_NAMESPACE_STD 108 109#endif // _LIBCPP_STD_VER >= 14 110 111_LIBCPP_POP_MACROS 112 113#endif //_LIBCPP_LATCH 114