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//===------------------------- barrier.cpp ---------------------------------===//
//
// 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 <__config>
#ifndef _LIBCPP_HAS_NO_THREADS
#include <barrier>
#include <thread>
_LIBCPP_BEGIN_NAMESPACE_STD
#if !defined(_LIBCPP_HAS_NO_TREE_BARRIER) && (_LIBCPP_STD_VER > 11)
class __barrier_algorithm_base {
public:
struct alignas(64) /* naturally-align the heap state */ __state_t
{
struct {
__atomic_base<__barrier_phase_t> __phase = ATOMIC_VAR_INIT(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_STD_VER >= 11)
_LIBCPP_END_NAMESPACE_STD
#endif //_LIBCPP_HAS_NO_THREADS
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