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-/**
- * Copyright (C) 2022-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/util/clock_source.h"
-#include "mongo/util/concurrency/mutex.h"
-#include "mongo/util/system_clock_source.h"
-
-namespace mongo {
-
-/**
- * Rate limiting is used to put a bound on the number of requests to a certain resource over a fixed
- * time window. This implementation is approximate in the sense that it may permit the bound to
- * exceeded. The bound is approximate as a trade off to reduce contention on internal resources.
- */
-class RateLimiting {
- using RequestCount = uint32_t;
-
-public:
- /*
- * Constructor for a rate limiter. Specify the number of requests you want to take place, as
- * well as the time period in milliseconds.
- */
- RateLimiting(RequestCount samplingRate,
- Milliseconds timePeriod = Seconds{1},
- ClockSource* clockSource = nullptr);
-
- /*
- * Getter for the sampling rate.
- */
- RequestCount getSamplingRate() {
- return _samplingRate.load();
- }
-
- /*
- * Setter for the sampling rate.
- */
- void setSamplingRate(RequestCount samplingRate) {
- _samplingRate.store(samplingRate);
- }
-
- /*
- * A simple method for rate limiting. Returns false if we have reached the request limit for the
- * current time window; otherwise, returns true and adds the request to the count for the
- * current window. If we have passed the end of the previous window, the slate is wiped clean.
- */
- bool handleRequestFixedWindow();
-
- /*
- * A method that ensures a more steady rate of requests. Rather than only looking at the current
- * time block, this method simulates a sliding window to estimate how many requests occurred in
- * the last full time period. Like the above, returns whether the request should be handled, and
- * resets the window if enough time has passed.
- */
- bool handleRequestSlidingWindow();
-
-private:
- /*
- * Resets the current window if it has ended. Returns the current time. This must be called in
- * the beginning of each handleRequest...() method.
- */
- Date_t tickWindow();
-
- /*
- * Clock source used to track time.
- */
- ClockSource* const _clockSource;
-
- /*
- * Sampling rate is the bound on the number of requests we want to admit per window.
- */
- AtomicWord<RequestCount> _samplingRate;
-
- /*
- * Time period is the window size in ms.
- */
- const Milliseconds _timePeriod;
-
- /*
- * Window start.
- */
- Date_t _windowStart;
-
- /*
- * Count of requests handled in the previous window.
- */
- RequestCount _prevCount;
-
- /*
- * Count of requests handled in the current window.
- */
- RequestCount _currentCount;
-
- /*
- * Mutex used when reading/writing the window.
- */
- SimpleMutex _windowMutex;
-};
-} // namespace mongo