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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
/*
* @author Keith Adams <kma@fb.com>
* @author Jordan DeLong <delong.j@fb.com>
*/
#include <cstdint>
#include <thread>
#include <folly/portability/Asm.h>
namespace folly {
//////////////////////////////////////////////////////////////////////
namespace detail {
/*
* A helper object for the contended case. Starts off with eager
* spinning, and falls back to sleeping for small quantums.
*/
class Sleeper {
static const uint32_t kMaxActiveSpin = 4000;
uint32_t spinCount;
public:
Sleeper() noexcept : spinCount(0) {}
static void sleep() noexcept {
/*
* Always sleep 0.5ms, assuming this will make the kernel put
* us down for whatever its minimum timer resolution is (in
* linux this varies by kernel version from 1ms to 10ms).
*/
std::this_thread::sleep_for(std::chrono::microseconds{500});
}
void wait() noexcept {
if (spinCount < kMaxActiveSpin) {
++spinCount;
asm_volatile_pause();
} else {
sleep();
}
}
};
} // namespace detail
} // namespace folly
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