Coverage Report

Created: 2020-10-24 06:27

/Users/buildslave/jenkins/workspace/coverage/llvm-project/libcxx/src/barrier.cpp
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//===------------------------- barrier.cpp ---------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include <__config>
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#ifndef _LIBCPP_HAS_NO_THREADS
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#include <barrier>
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#include <thread>
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_LIBCPP_BEGIN_NAMESPACE_STD
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#if !defined(_LIBCPP_HAS_NO_TREE_BARRIER) && (_LIBCPP_STD_VER > 11)
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class __barrier_algorithm_base {
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public:
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    struct alignas(64) /* naturally-align the heap state */ __state_t
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    {
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        struct {
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            __atomic_base<__barrier_phase_t> __phase = ATOMIC_VAR_INIT(0);
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        } __tickets[64];
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    };
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    ptrdiff_t&              __expected;
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    unique_ptr<__state_t[]> __state;
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    _LIBCPP_HIDDEN
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    __barrier_algorithm_base(ptrdiff_t& __expected)
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        : __expected(__expected)
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    {
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        size_t const __count = (__expected + 1) >> 1;
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        __state = unique_ptr<__state_t[]>(new __state_t[__count]);
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    }
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    _LIBCPP_HIDDEN
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    bool __arrive(__barrier_phase_t __old_phase)
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    {
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        __barrier_phase_t const __half_step = __old_phase + 1,
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                                __full_step = __old_phase + 2;
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        size_t __current_expected = __expected,
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            __current = hash<thread::id>()(this_thread::get_id()) % ((__expected + 1) >> 1);
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        for(int __round = 0;; ++__round) {
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            if(__current_expected <= 1)
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                return true;
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            size_t const __end_node = ((__current_expected + 1) >> 1),
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                         __last_node = __end_node - 1;
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            for(;;++__current) {
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                if(__current == __end_node)
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                __current = 0;
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                __barrier_phase_t expect = __old_phase;
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                if(__current == __last_node && (__current_expected & 1))
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                {
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                    if(__state[__current].__tickets[__round].__phase.compare_exchange_strong(expect, __full_step, memory_order_acq_rel))
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                        break;    // I'm 1 in 1, go to next __round
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                }
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                else if(__state[__current].__tickets[__round].__phase.compare_exchange_strong(expect, __half_step, memory_order_acq_rel))
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                {
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                    return false; // I'm 1 in 2, done with arrival
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                }
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                else if(expect == __half_step)
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                {
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                    if(__state[__current].__tickets[__round].__phase.compare_exchange_strong(expect, __full_step, memory_order_acq_rel))
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                        break;    // I'm 2 in 2, go to next __round
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                }
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            }
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            __current_expected = __last_node + 1;
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            __current >>= 1;
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        }
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    }
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};
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_LIBCPP_EXPORTED_FROM_ABI
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__barrier_algorithm_base * __construct_barrier_algorithm_base(ptrdiff_t& __expected)
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{
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    return new __barrier_algorithm_base(__expected);
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}
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_LIBCPP_EXPORTED_FROM_ABI
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bool __arrive_barrier_algorithm_base(__barrier_algorithm_base* __barrier,
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                                     __barrier_phase_t __old_phase)
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{
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    return __barrier->__arrive(__old_phase);
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}
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_LIBCPP_EXPORTED_FROM_ABI
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void __destroy_barrier_algorithm_base(__barrier_algorithm_base* __barrier)
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{
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    delete __barrier;
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}
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#endif //!defined(_LIBCPP_HAS_NO_TREE_BARRIER) && (_LIBCPP_STD_VER >= 11)
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_LIBCPP_END_NAMESPACE_STD
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#endif //_LIBCPP_HAS_NO_THREADS