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/**
* Copyright (C) 2016 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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 <thread>
#include "mongo/base/disallow_copying.h"
#include "mongo/platform/atomic_word.h"
#include "mongo/stdx/condition_variable.h"
#include "mongo/stdx/memory.h"
#include "mongo/stdx/mutex.h"
#include "mongo/stdx/thread.h"
#include "mongo/util/clock_source.h"
#include "mongo/util/time_support.h"
namespace mongo {
/**
* A clock source that uses a periodic timer to build a low-resolution, fast-to-read clock.
* Essentially uses a background thread that repeatedly sleeps for X amount of milliseconds
* and wakes up to store the current time. If nothing reads the time for a whole granularity, the
* thread will sleep until it is needed again.
*/
class BackgroundThreadClockSource final : public ClockSource {
MONGO_DISALLOW_COPYING(BackgroundThreadClockSource);
public:
BackgroundThreadClockSource(std::unique_ptr<ClockSource> clockSource, Milliseconds granularity);
~BackgroundThreadClockSource() override;
Milliseconds getPrecision() override;
Date_t now() override;
Status setAlarm(Date_t when, stdx::function<void()> action) override;
/**
* Doesn't count as a call to now() for determining whether this ClockSource is idle.
*
* Unlike now(), returns Date_t() if the thread is currently paused.
*/
Date_t peekNowForTest() const {
return Date_t::fromMillisSinceEpoch(_current.load());
}
private:
Date_t _slowNow();
void _startTimerThread();
int64_t _updateCurrent_inlock();
const std::unique_ptr<ClockSource> _clockSource;
AtomicInt64 _current{0}; // 0 if _timer is paused due to idleness.
AtomicBool _timerWillPause{true}; // If true when _timer wakes up, it will pause.
const Milliseconds _granularity;
stdx::mutex _mutex;
stdx::condition_variable _condition;
bool _inShutdown = false;
bool _started = false;
stdx::thread _timer;
};
} // namespace mongo
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