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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 <map>
#include <memory>
#include "mongo/base/status.h"
#include "mongo/stdx/mutex.h"
#include "mongo/util/clock_source.h"
#include "mongo/util/functional.h"
#include "mongo/util/future.h"
namespace mongo {
/*
* An alarm scheduler will fill a Future<void> at some time in the future and allow the caller to
* cancel specific alarms by opaque ID.
*
* All alarm service implementations take a ClockSource and all Date_t/Durations used to schedule
* alarms must be in relation to that ClockSource's now() and epoch.
*
* A scheduler won't actually process alarms. Some executor must be calling processExpiredAlarms()
* in order for alarms to fire.
*/
class AlarmScheduler {
public:
/*
* This type gets returned when an alarm is scheduled and allows you to cancel the alarm.
*
* Once this handle is destroyed, the alarm will still be processed if it is still outstanding
* and there will be no way to cancel it.
*/
class Handle {
public:
virtual ~Handle() = default;
/*
* Cancels the alarm if it has not already been fulfilled. If the alarm has already been
* fulfilled this returns an ErrorCodes::AlarmAlreadyFulfilled error
*/
virtual Status cancel() = 0;
};
using SharedHandle = std::shared_ptr<Handle>;
using AlarmCount = uint64_t;
explicit AlarmScheduler(ClockSource* clockSource) : _clockSource(clockSource) {}
virtual ~AlarmScheduler() = default;
/*
* Fulfills all outstanding alarms with CallbackCanceled. Memory associated with the scheduler
* may not be freed until the last outstanding Handle is destroyed, however there should be
* no broken promises.
*
* This will be called implicitly by the destructor.
*/
virtual void clearAllAlarms() = 0;
/*
* Clears all alarms as above, and prevents any new alarms from being scheduled. Calls to
* alarmAt will return a ready Future with a ShutdownInProgress error code.
*/
virtual void clearAllAlarmsAndShutdown() = 0;
struct Alarm {
Future<void> future;
SharedHandle handle;
};
/*
* Schedules an alarm some milliseconds from now().
*/
Alarm alarmFromNow(Milliseconds time) {
return alarmAt(_clockSource->now() + time);
};
/*
* Schedules an alarm at a specific time on the service's clock source.
*/
virtual Alarm alarmAt(Date_t time) = 0;
/*
* Registers a callback that will be called when a new alarm has been registered.
*
* The hook will be called with a Date_t representing the next time an alarm will expire after
* all internal locks have been released. This can be used to unblock between calling
* processExpiredAlarms() with a new amount of time to block for.
*/
using AlarmRegisterHook = unique_function<void(Date_t, const std::shared_ptr<AlarmScheduler>&)>;
void setAlarmRegisterHook(AlarmRegisterHook onAlarmHook) {
_registerHook = std::move(onAlarmHook);
}
/*
* Processes all alarms that have expired as of now(). If maxAlarms is not boost::none, then
* this will only expire that many alarms before returning.
*
* Returns the number of alarms that were expired by this call.
*/
using AlarmExpireHook = unique_function<bool(AlarmCount)>;
virtual void processExpiredAlarms(boost::optional<AlarmExpireHook> hook = boost::none) = 0;
/*
* Returns the Date_t of the next scheduled alarm.
*/
virtual Date_t nextAlarm() = 0;
virtual ClockSource* clockSource() const {
return _clockSource;
}
protected:
void callRegisterHook(Date_t nextAlarm, const std::shared_ptr<AlarmScheduler>& which) {
if (_registerHook) {
_registerHook(nextAlarm, which);
}
}
private:
AlarmRegisterHook _registerHook;
ClockSource* const _clockSource;
};
/*
* Implements a basic alarm scheduler based on a multimap of date_t to promise.
*
* Scheduling an alarm takes O(log(n)) where n is the number of outstanding alarms.
* Canceling an alarm is done in constant time.
* Processing alarms is done in constant time.
*/
class AlarmSchedulerPrecise : public AlarmScheduler,
public std::enable_shared_from_this<AlarmSchedulerPrecise> {
public:
explicit AlarmSchedulerPrecise(ClockSource* clockSource) : AlarmScheduler(clockSource) {}
~AlarmSchedulerPrecise();
void clearAllAlarms() override;
void clearAllAlarmsAndShutdown() override;
Alarm alarmAt(Date_t time) override;
void processExpiredAlarms(boost::optional<AlarmExpireHook> hook) override;
Date_t nextAlarm() override;
private:
class HandleImpl;
enum AlarmState { kOutstanding, kFulfilled, kAbandoned };
struct AlarmData {
explicit AlarmData(Promise<void> promise_) : promise(std::move(promise_)) {}
std::weak_ptr<HandleImpl> handle;
Promise<void> promise;
};
using AlarmMap = std::multimap<Date_t, AlarmData>;
using AlarmMapIt = AlarmMap::iterator;
void _clearAllAlarmsImpl(stdx::unique_lock<stdx::mutex>& lk);
stdx::mutex _mutex;
bool _shutdown = false;
AlarmMap _alarms;
};
} // namespace mongo
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