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 #if !defined(_LIBCPP_HAS_NO_TREE_BARRIER) 15 16 class __barrier_algorithm_base { 17 public: 18 struct alignas(64) /* naturally-align the heap state */ __state_t { 19 struct { 20 __atomic_base<__barrier_phase_t> __phase{0}; 21 } __tickets[64]; 22 }; 23 24 ptrdiff_t& __expected; 25 unique_ptr<__state_t[]> __state; 26 27 _LIBCPP_HIDDEN __barrier_algorithm_base(ptrdiff_t& __expected) : __expected(__expected) { 28 size_t const __count = (__expected + 1) >> 1; 29 __state = unique_ptr<__state_t[]>(new __state_t[__count]); 30 } 31 _LIBCPP_HIDDEN bool __arrive(__barrier_phase_t __old_phase) { 32 __barrier_phase_t const __half_step = __old_phase + 1, __full_step = __old_phase + 2; 33 size_t __current_expected = __expected, 34 __current = hash<thread::id>()(this_thread::get_id()) % ((__expected + 1) >> 1); 35 for (int __round = 0;; ++__round) { 36 if (__current_expected <= 1) 37 return true; 38 size_t const __end_node = ((__current_expected + 1) >> 1), __last_node = __end_node - 1; 39 for (;; ++__current) { 40 if (__current == __end_node) 41 __current = 0; 42 __barrier_phase_t expect = __old_phase; 43 if (__current == __last_node && (__current_expected & 1)) { 44 if (__state[__current].__tickets[__round].__phase.compare_exchange_strong( 45 expect, __full_step, memory_order_acq_rel)) 46 break; // I'm 1 in 1, go to next __round 47 } else if (__state[__current].__tickets[__round].__phase.compare_exchange_strong( 48 expect, __half_step, memory_order_acq_rel)) { 49 return false; // I'm 1 in 2, done with arrival 50 } else if (expect == __half_step) { 51 if (__state[__current].__tickets[__round].__phase.compare_exchange_strong( 52 expect, __full_step, memory_order_acq_rel)) 53 break; // I'm 2 in 2, go to next __round 54 } 55 } 56 __current_expected = __last_node + 1; 57 __current >>= 1; 58 } 59 } 60 }; 61 62 _LIBCPP_EXPORTED_FROM_ABI __barrier_algorithm_base* __construct_barrier_algorithm_base(ptrdiff_t& __expected) { 63 return new __barrier_algorithm_base(__expected); 64 } 65 _LIBCPP_EXPORTED_FROM_ABI bool 66 __arrive_barrier_algorithm_base(__barrier_algorithm_base* __barrier, __barrier_phase_t __old_phase) { 67 return __barrier->__arrive(__old_phase); 68 } 69 _LIBCPP_EXPORTED_FROM_ABI void __destroy_barrier_algorithm_base(__barrier_algorithm_base* __barrier) { 70 delete __barrier; 71 } 72 73 #endif // !defined(_LIBCPP_HAS_NO_TREE_BARRIER) 74 75 _LIBCPP_END_NAMESPACE_STD 76