89 lines
2.4 KiB
C
89 lines
2.4 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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#include <algorithm>
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#include <chrono>
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#include <thread>
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#include <folly/portability/Asm.h>
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#include <folly/synchronization/WaitOptions.h>
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namespace folly {
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namespace detail {
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enum class spin_result {
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success, // condition passed
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timeout, // exceeded deadline
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advance, // exceeded current wait-options component timeout
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};
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template <typename Clock, typename Duration, typename F>
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spin_result spin_pause_until(
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std::chrono::time_point<Clock, Duration> const& deadline,
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WaitOptions const& opt,
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F f) {
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if (opt.spin_max() <= opt.spin_max().zero()) {
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return spin_result::advance;
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}
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auto tbegin = Clock::now();
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while (true) {
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if (f()) {
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return spin_result::success;
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}
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auto const tnow = Clock::now();
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if (tnow >= deadline) {
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return spin_result::timeout;
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}
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// Backward time discontinuity in Clock? revise pre_block starting point
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tbegin = std::min(tbegin, tnow);
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if (tnow >= tbegin + opt.spin_max()) {
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return spin_result::advance;
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}
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// The pause instruction is the polite way to spin, but it doesn't
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// actually affect correctness to omit it if we don't have it. Pausing
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// donates the full capabilities of the current core to its other
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// hyperthreads for a dozen cycles or so.
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asm_volatile_pause();
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}
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}
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template <typename Clock, typename Duration, typename F>
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spin_result spin_yield_until(
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std::chrono::time_point<Clock, Duration> const& deadline,
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F f) {
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while (true) {
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if (f()) {
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return spin_result::success;
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}
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auto const max = std::chrono::time_point<Clock, Duration>::max();
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if (deadline != max && Clock::now() >= deadline) {
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return spin_result::timeout;
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}
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std::this_thread::yield();
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}
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}
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} // namespace detail
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} // namespace folly
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