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-exception 6 // 7 //===----------------------------------------------------------------------===// 8 9 #include <barrier> 10 #include <thread> 11 12 _LIBCPP_BEGIN_NAMESPACE_STD 13 14 class __barrier_algorithm_base { 15 public: 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 __round 45 } 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 arrival 48 } 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 __round 52 } 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 64 __arrive_barrier_algorithm_base(__barrier_algorithm_base* __barrier, __barrier_phase_t __old_phase) noexcept { 65 return __barrier->__arrive(__old_phase); 66 } 67 _LIBCPP_EXPORTED_FROM_ABI void __destroy_barrier_algorithm_base(__barrier_algorithm_base* __barrier) noexcept { 68 delete __barrier; 69 } 70 71 _LIBCPP_END_NAMESPACE_STD 72