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 | |