68 lines
1.7 KiB
C++
68 lines
1.7 KiB
C++
/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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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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#pragma once
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/*
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* @author Keith Adams <kma@fb.com>
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* @author Jordan DeLong <delong.j@fb.com>
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*/
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#include <chrono>
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#include <cstdint>
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#include <thread>
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#include <folly/portability/Asm.h>
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namespace folly {
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//////////////////////////////////////////////////////////////////////
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namespace detail {
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/*
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* A helper object for the contended case. Starts off with eager
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* spinning, and falls back to sleeping for small quantums.
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*/
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class Sleeper {
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const std::chrono::nanoseconds delta;
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uint32_t spinCount;
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static constexpr uint32_t kMaxActiveSpin = 4000;
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public:
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static constexpr std::chrono::nanoseconds kMinYieldingSleep =
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std::chrono::microseconds(500);
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constexpr Sleeper() noexcept : delta(kMinYieldingSleep), spinCount(0) {}
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explicit Sleeper(std::chrono::nanoseconds d) noexcept
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: delta(d), spinCount(0) {}
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void wait() noexcept {
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if (spinCount < kMaxActiveSpin) {
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++spinCount;
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asm_volatile_pause();
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} else {
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/* sleep override */
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std::this_thread::sleep_for(delta);
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}
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}
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};
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} // namespace detail
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} // namespace folly
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