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/**
* Copyright (C) 2020-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 <cstddef>
#include <cstdint>
#include <functional>
#include <type_traits>
namespace mongo {
/**
* During the runtime planning phase this tracker is used to track the progress of the work done
* so far. A plan stage in a candidate execution tree may supply the number of documents it has
* processed, or the number of physical reads performed, and the tracker will use it to check if
* the execution plan has progressed enough.
*/
class TrialRunTracker final {
public:
/**
* The type of metric which can be collected and tracked during a trial run.
*/
enum TrialRunMetric : uint8_t {
// Number of documents returned during a trial run.
kNumResults,
// Number of physical reads performed during a trial run. Once a storage cursor advances,
// it counts as a single physical read.
kNumReads,
// Must always be the last element to hold the number of element in the enum.
kLastElem
};
/**
* Constructs a 'TrialRunTracker' which indicates that the trial period is over when any
* 'TrialRunMetric' exceeds the maximum provided at construction.
*
* Callers can also pass a value of zero to indicate that the given metric should not be
* tracked.
*/
template <typename... MaxMetrics,
std::enable_if_t<sizeof...(MaxMetrics) == TrialRunMetric::kLastElem, int> = 0>
TrialRunTracker(MaxMetrics... maxMetrics) : _maxMetrics{maxMetrics...} {}
/**
* Constructs a 'TrialRunTracker' that also has an '_onTrialEnd' function, which gets called
* when any 'TrialRunMetric' exceeds its maximum. When an '_onTrialEnd' callback is present, it
* must return true for 'trackProgress' to return true. By returning false, '_onTrialEnd' can
* prevent tracking from halting plan execution, thereby upgrading a trial run to a normal run.
*/
template <typename... MaxMetrics>
TrialRunTracker(std::function<bool()> onTrialEnd, MaxMetrics... maxMetrics)
: TrialRunTracker{maxMetrics...} {
_onTrialEnd = std::move(onTrialEnd);
}
/**
* Increments the trial run metric specified as a template parameter 'metric' by the
* 'metricIncrement' value and, if the updated metric value has exceeded its maximum, calls the
* '_onTrialEnd' if there is one and returns true (unless '_onTrialEnd' returned false).
*
* This is a no-op, and will return false, if the given metric is not being tracked by this
* 'TrialRunTracker'.
*
* If the metric has already exceeded its maximum value before this call, this method
* returns 'true' immediately without incrementing the metric.
*/
template <TrialRunMetric metric>
bool trackProgress(size_t metricIncrement) {
static_assert(metric >= 0 && metric < sizeof(_metrics) / sizeof(size_t));
if (_maxMetrics[metric] == 0) {
// This metric is not being tracked.
return false;
}
if (_done) {
return true;
}
_metrics[metric] += metricIncrement;
if (_metrics[metric] > _maxMetrics[metric] && callOnTrialEnd()) {
_done = true;
}
return _done;
}
template <TrialRunMetric metric>
size_t getMetric() const {
static_assert(metric >= 0 && metric < sizeof(_metrics) / sizeof(size_t));
return _metrics[metric];
}
bool callOnTrialEnd() {
return !_onTrialEnd || _onTrialEnd();
}
private:
const size_t _maxMetrics[TrialRunMetric::kLastElem];
size_t _metrics[TrialRunMetric::kLastElem]{0};
bool _done{false};
std::function<bool()> _onTrialEnd{};
};
} // namespace mongo
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