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/**
* Copyright (C) 2023-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 "mongo/stdx/condition_variable.h"
#include <queue>
#include <thread>
#include "mongo/platform/atomic_word.h"
#include "mongo/stdx/thread.h"
#include "mongo/util/duration.h"
#include "mongo/util/future.h"
#include "mongo/util/tick_source_mock.h"
namespace mongo::workload_simulation {
/**
* This class coordinates event processing and clock advancement for a simulated workload.
*/
class EventQueue {
public:
using time_type = TickSource::Tick;
enum class WaitType { Event, Observer };
private:
using promise_type = SharedPromise<void>;
using storage_type = std::tuple<time_type, std::unique_ptr<promise_type>, std::string>;
struct time_greater {
bool operator()(const storage_type& lhs, const storage_type& rhs) const {
return std::get<0>(lhs) > std::get<0>(rhs);
}
};
using queue_type = std::priority_queue<storage_type, std::vector<storage_type>, time_greater>;
public:
/**
* @param tickSource Mock clock, which should only be advanced by this 'EventQueue'.
* @param actorCount During normal operation, the processing thread will block until it
* contains at least as many events as the number returned by
* 'actorCount()'. The return value of this function should reflect the
* current state of the system (e.g. it should be dynamic if the number of
* actors active at a given time can change).
*/
EventQueue(TickSourceMock<Nanoseconds>& tickSource, std::function<size_t()> actorCount);
/**
* Begin normal operation. The processing thread will wait until it has at least 'actorCount()'
* Event-type operations queued. Once it does, it will process all operations that are queued
* with times at most that of the minimum Event-type operation in time order, advancing the
* clock to the current operation time.
*/
void start();
/**
* End normal operation. The queue will now drain events immediately, rather than waiting for
* 'actorCount()' events to accrue. Subsequent calls to 'wait_for' will return immediately.
*/
void prepareStop();
/**
* Stops the processing thread.
*/
void stop();
/**
* Remove any remaining requests from the queue immediately.
*/
void clear();
/**
* Wait for the clock to advance a specified duration. Blocking.
*
* @param d Duration to wait.
* @param t Operation type. An 'Event' will count towards the 'actorCount()' and potentially
* advance the clock. An 'Observer' will not, and will only be processed if an
* 'Event' advances the clock sufficiently.
* @return Whether it actually waited. May return 'false' if 'prepareStop' was called.
*/
template <typename Duration>
bool wait_for(Duration d, WaitType t);
private:
void _processQueues();
bool _haveEventToProcess();
bool _haveEventAtOrBeforeTime(time_type t);
time_type _nextEventTime();
std::pair<const storage_type*, queue_type*> _nextEventToProcess();
mutable Mutex _mutex = MONGO_MAKE_LATCH("EventQueue::_mutex");
mutable stdx::condition_variable _cv;
TickSourceMock<Nanoseconds>& _tickSource;
std::function<size_t()> _actorCount;
queue_type _eventQueue;
queue_type _observerQueue;
stdx::thread _timer;
AtomicWord<bool> _stopping{false};
AtomicWord<bool> _draining{false};
};
} // namespace mongo::workload_simulation
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