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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
#pragma once
#include <algorithm>
#include <chrono>
#include <thread>
#include <folly/portability/Asm.h>
#include <folly/synchronization/WaitOptions.h>
namespace folly {
namespace detail {
enum class spin_result {
success, // condition passed
timeout, // exceeded deadline
advance, // exceeded current wait-options component timeout
};
template <typename Clock, typename Duration, typename F>
spin_result spin_pause_until(
std::chrono::time_point<Clock, Duration> const& deadline,
WaitOptions const& opt,
F f) {
if (opt.spin_max() <= opt.spin_max().zero()) {
return spin_result::advance;
}
auto tbegin = Clock::now();
while (true) {
if (f()) {
return spin_result::success;
}
auto const tnow = Clock::now();
if (tnow >= deadline) {
return spin_result::timeout;
}
// Backward time discontinuity in Clock? revise pre_block starting point
tbegin = std::min(tbegin, tnow);
if (tnow >= tbegin + opt.spin_max()) {
return spin_result::advance;
}
// The pause instruction is the polite way to spin, but it doesn't
// actually affect correctness to omit it if we don't have it. Pausing
// donates the full capabilities of the current core to its other
// hyperthreads for a dozen cycles or so.
asm_volatile_pause();
}
}
template <typename Clock, typename Duration, typename F>
spin_result spin_yield_until(
std::chrono::time_point<Clock, Duration> const& deadline,
F f) {
while (true) {
if (f()) {
return spin_result::success;
}
auto const max = std::chrono::time_point<Clock, Duration>::max();
if (deadline != max && Clock::now() >= deadline) {
return spin_result::timeout;
}
std::this_thread::yield();
}
}
} // namespace detail
} // namespace folly
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