73 lines · cpp
1//===----------------------------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#include <barrier>10#include <thread>11 12_LIBCPP_BEGIN_NAMESPACE_STD13 14class __barrier_algorithm_base {15public:16 struct alignas(64) /* naturally-align the heap state */ __state_t {17 struct {18 atomic<__barrier_phase_t> __phase{0};19 } __tickets[64];20 };21 22 ptrdiff_t& __expected_;23 unique_ptr<__state_t[]> __state_;24 25 _LIBCPP_HIDDEN __barrier_algorithm_base(ptrdiff_t& __expected) : __expected_(__expected) {26 size_t const __count = (__expected + 1) >> 1;27 __state_ = unique_ptr<__state_t[]>(new __state_t[__count]);28 }29 _LIBCPP_HIDDEN bool __arrive(__barrier_phase_t __old_phase) {30 __barrier_phase_t const __half_step = __old_phase + 1, __full_step = __old_phase + 2;31 size_t __current_expected = __expected_,32 __current = hash<thread::id>()(this_thread::get_id()) % ((__expected_ + 1) >> 1);33 for (int __round = 0;; ++__round) {34 if (__current_expected <= 1)35 return true;36 size_t const __end_node = ((__current_expected + 1) >> 1), __last_node = __end_node - 1;37 for (;; ++__current) {38 if (__current == __end_node)39 __current = 0;40 __barrier_phase_t expect = __old_phase;41 if (__current == __last_node && (__current_expected & 1)) {42 if (__state_[__current].__tickets[__round].__phase.compare_exchange_strong(43 expect, __full_step, memory_order_acq_rel))44 break; // I'm 1 in 1, go to next __round45 } else if (__state_[__current].__tickets[__round].__phase.compare_exchange_strong(46 expect, __half_step, memory_order_acq_rel)) {47 return false; // I'm 1 in 2, done with arrival48 } else if (expect == __half_step) {49 if (__state_[__current].__tickets[__round].__phase.compare_exchange_strong(50 expect, __full_step, memory_order_acq_rel))51 break; // I'm 2 in 2, go to next __round52 }53 }54 __current_expected = __last_node + 1;55 __current >>= 1;56 }57 }58};59 60_LIBCPP_EXPORTED_FROM_ABI __barrier_algorithm_base* __construct_barrier_algorithm_base(ptrdiff_t& __expected) {61 return new __barrier_algorithm_base(__expected);62}63_LIBCPP_EXPORTED_FROM_ABI bool __arrive_barrier_algorithm_base(64 _LIBCPP_NOESCAPE __barrier_algorithm_base* __barrier, __barrier_phase_t __old_phase) noexcept {65 return __barrier->__arrive(__old_phase);66}67_LIBCPP_EXPORTED_FROM_ABI void68__destroy_barrier_algorithm_base(_LIBCPP_NOESCAPE __barrier_algorithm_base* __barrier) noexcept {69 delete __barrier;70}71 72_LIBCPP_END_NAMESPACE_STD73