76 lines
2.5 KiB
C++
76 lines
2.5 KiB
C++
/*
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* Copyright (C) 2015 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <utils/CyclicBarrier.h>
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#include <algorithm>
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namespace utils {
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CyclicBarrier::CyclicBarrier(size_t num_threads) noexcept
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: m_num_threads(std::max(size_t(1), num_threads)) {
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}
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size_t CyclicBarrier::getThreadCount() const noexcept {
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return m_num_threads;
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}
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size_t CyclicBarrier::getWaitingThreadCount() const noexcept {
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std::lock_guard<Mutex> guard(m_lock);
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return m_trapped_threads;
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}
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void CyclicBarrier::reset() noexcept {
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std::unique_lock<Mutex> guard(m_lock);
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m_state = State::TRAP;
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m_trapped_threads = 0;
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m_released_threads = 0;
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guard.unlock(); // avoid threads to lock again immediately
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m_cv.notify_all();
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}
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void CyclicBarrier::await() noexcept {
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std::unique_lock<Mutex> guard(m_lock);
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// we're releasing old threads, wait until we're done with that
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m_cv.wait(guard, [this]{ return m_state != State::RELEASE; });
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// This is the last thread that will be trapped in the barrier
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if (m_trapped_threads == m_num_threads-1) {
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std::swap(m_released_threads, m_trapped_threads);
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// release currently trapped threads
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m_state = State::RELEASE;
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m_cv.notify_all();
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// wait for all previously trapped threads to be released
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m_cv.wait(guard, [this]{ return m_released_threads == 0; });
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m_state = State::TRAP;
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guard.unlock(); // avoid threads to lock again immediately
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m_cv.notify_all();
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} else {
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++m_trapped_threads;
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m_cv.wait(guard, [this]{ return m_state == State::RELEASE; });
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if (--m_released_threads == 0) {
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// no more threads to be released, we need to notify the last one which is
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// waiting for the m_released_threads queue to become empty and will switch the
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// state back to State::TRAP.
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guard.unlock(); // avoid threads to lock again immediately
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m_cv.notify_all();
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}
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}
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}
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} // namespace utils
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