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
__barrier_algorithm_base(ptrdiff_t & __expected)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 }
__arrive(__barrier_phase_t __old_phase)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
__construct_barrier_algorithm_base(ptrdiff_t & __expected)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
__arrive_barrier_algorithm_base(__barrier_algorithm_base * __barrier,__barrier_phase_t __old_phase)66 __arrive_barrier_algorithm_base(__barrier_algorithm_base* __barrier, __barrier_phase_t __old_phase) noexcept {
67 return __barrier->__arrive(__old_phase);
68 }
__destroy_barrier_algorithm_base(__barrier_algorithm_base * __barrier)69 _LIBCPP_EXPORTED_FROM_ABI void __destroy_barrier_algorithm_base(__barrier_algorithm_base* __barrier) noexcept {
70 delete __barrier;
71 }
72
73 #endif // !defined(_LIBCPP_HAS_NO_TREE_BARRIER)
74
75 _LIBCPP_END_NAMESPACE_STD
76