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//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include <barrier>
#include <thread>
_LIBCPP_BEGIN_NAMESPACE_STD
#if !defined(_LIBCPP_HAS_NO_TREE_BARRIER)
class __barrier_algorithm_base {
public:
struct alignas(64) /* naturally-align the heap state */ __state_t {
struct {
__atomic_base<__barrier_phase_t> __phase{0};
} __tickets[64];
};
ptrdiff_t& __expected;
unique_ptr<__state_t[]> __state;
_LIBCPP_HIDDEN __barrier_algorithm_base(ptrdiff_t& __expected) : __expected(__expected) {
size_t const __count = (__expected + 1) >> 1;
__state = unique_ptr<__state_t[]>(new __state_t[__count]);
}
_LIBCPP_HIDDEN bool __arrive(__barrier_phase_t __old_phase) {
__barrier_phase_t const __half_step = __old_phase + 1, __full_step = __old_phase + 2;
size_t __current_expected = __expected,
__current = hash<thread::id>()(this_thread::get_id()) % ((__expected + 1) >> 1);
for (int __round = 0;; ++__round) {
if (__current_expected <= 1)
return true;
size_t const __end_node = ((__current_expected + 1) >> 1), __last_node = __end_node - 1;
for (;; ++__current) {
if (__current == __end_node)
__current = 0;
__barrier_phase_t expect = __old_phase;
if (__current == __last_node && (__current_expected & 1)) {
if (__state[__current].__tickets[__round].__phase.compare_exchange_strong(
expect, __full_step, memory_order_acq_rel))
break; // I'm 1 in 1, go to next __round
} else if (__state[__current].__tickets[__round].__phase.compare_exchange_strong(
expect, __half_step, memory_order_acq_rel)) {
return false; // I'm 1 in 2, done with arrival
} else if (expect == __half_step) {
if (__state[__current].__tickets[__round].__phase.compare_exchange_strong(
expect, __full_step, memory_order_acq_rel))
break; // I'm 2 in 2, go to next __round
}
}
__current_expected = __last_node + 1;
__current >>= 1;
}
}
};
_LIBCPP_EXPORTED_FROM_ABI __barrier_algorithm_base* __construct_barrier_algorithm_base(ptrdiff_t& __expected) {
return new __barrier_algorithm_base(__expected);
}
_LIBCPP_EXPORTED_FROM_ABI bool
__arrive_barrier_algorithm_base(__barrier_algorithm_base* __barrier, __barrier_phase_t __old_phase) {
return __barrier->__arrive(__old_phase);
}
_LIBCPP_EXPORTED_FROM_ABI void __destroy_barrier_algorithm_base(__barrier_algorithm_base* __barrier) {
delete __barrier;
}
#endif // !defined(_LIBCPP_HAS_NO_TREE_BARRIER)
_LIBCPP_END_NAMESPACE_STD
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