69 lines
1.7 KiB
C
69 lines
1.7 KiB
C
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/*
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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 <cstdint>
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#include <folly/portability/Asm.h>
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#include <folly/portability/Time.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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static const uint32_t kMaxActiveSpin = 4000;
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uint32_t spinCount;
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public:
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Sleeper() noexcept : spinCount(0) {}
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static void sleep() noexcept {
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/*
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* Always sleep 0.5ms, assuming this will make the kernel put
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* us down for whatever its minimum timer resolution is (in
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* linux this varies by kernel version from 1ms to 10ms).
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*/
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struct timespec ts = {0, 500000};
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nanosleep(&ts, nullptr);
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}
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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();
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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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