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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <chrono>
#include <memory>
#include <thread>
#include "mongo/platform/atomic_word.h"
#include "mongo/platform/mutex.h"
#include "mongo/stdx/condition_variable.h"
#include "mongo/stdx/thread.h"
#include "mongo/util/clock_source.h"
#include "mongo/util/time_support.h"
namespace mongo {
/**
* A clock source that reads the Date_t lastNow time and uses a background thread to ensure
* Date_t::now is called at least every X amount of milliseconds. If nothing reads the time for a
* whole granularity, the thread will sleep until it is needed again.
*
* Its now() returns Date_t::lastNow(), the passed in clock source is only used to control the
* sleeps for the background thread.
*/
class BackgroundThreadClockSource final : public ClockSource {
BackgroundThreadClockSource(const BackgroundThreadClockSource&) = delete;
BackgroundThreadClockSource& operator=(const BackgroundThreadClockSource&) = delete;
public:
BackgroundThreadClockSource(std::unique_ptr<ClockSource> clockSource, Milliseconds granularity);
~BackgroundThreadClockSource() override;
Milliseconds getPrecision() override;
Date_t now() override;
size_t timesPausedForTest();
private:
void _updateClockAndWakeTimerIfNeeded();
void _updateClock();
void _startTimerThread();
const std::unique_ptr<ClockSource> _clockSource;
// Expected transitions:
//
// Starting the clock source
// _ -> kTimerPaused
//
// Timer thread has woken from its timed sleep
// kTimerPaused
// kReaderRead -> kTimerWillPause
//
// Reader reads a time and the timer isn't paused
// kTimerWillPause -> kReaderHasRead
//
// Reader wakes up the timer thread
// kTimerPaused -> kReaderHasRead
enum States : uint8_t {
kReaderHasRead,
kTimerWillPause,
kTimerPaused,
};
AtomicWord<uint8_t> _state;
const Milliseconds _granularity;
stdx::mutex _mutex; // NOLINT
stdx::condition_variable _condition;
bool _inShutdown = false;
bool _started = false;
Date_t _lastUpdate;
// This is used exclusively for tests, to verify when we've actually gone to sleep
size_t _timesPaused = 0;
stdx::thread _timer;
};
} // namespace mongo
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