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Diffstat (limited to 'src/mongo/db/repl/delayable_timeout_callback.h')
| -rw-r--r-- | src/mongo/db/repl/delayable_timeout_callback.h | 159 |
1 files changed, 159 insertions, 0 deletions
diff --git a/src/mongo/db/repl/delayable_timeout_callback.h b/src/mongo/db/repl/delayable_timeout_callback.h new file mode 100644 index 00000000000..d1cb8e29f95 --- /dev/null +++ b/src/mongo/db/repl/delayable_timeout_callback.h @@ -0,0 +1,159 @@ +/** + * 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 <string> + +#include "mongo/base/status.h" +#include "mongo/executor/task_executor.h" +#include "mongo/util/time_support.h" + +namespace mongo { +namespace repl { + +/** + * The DelayableTimeoutCallback is a utility class which allows a callback to be scheduled on an + * executor at a given time, and then that time pushed back (later) arbitrarily often without + * rescheduling the call on the executor. The callback is never called with CallbackCanceled or + * ShutdownInProgress. + * + * All methods are thread safe, though isActive() and getNextCall() may return stale information + * if external synchronization is not used. The callback is called without any locks held. + */ +class DelayableTimeoutCallback { +public: + /** + * Creates a DelayableTimeoutCallback with the given executor and callback function. The + * DelayableTimeoutCallback is inactive (the callback is not scheduled) when constructed. + */ + DelayableTimeoutCallback(executor::TaskExecutor* executor, + executor::TaskExecutor::CallbackFn callback, + std::string timerName = std::string()) + : _executor(executor), _callback(std::move(callback)), _timerName(std::move(timerName)){}; + + ~DelayableTimeoutCallback(); + + /** + * If the timeout is scheduled, cancel it. The callback function will not be called. + */ + void cancel(); + + /** + * Schedule the timeout to occur at "when", regardless of if or when it is already scheduled. + * If it is already scheduled to occur after "when", it is canceled and rescheduled + * + * Returns status of the attempt to schedule on the executor. + */ + Status scheduleAt(Date_t when); + + /** + * Schedule the timeout to occur at "when" if it is not scheduled or scheduled to occur before + * "when". If it is already scheduled to occur before "when", this call has no effect. + * + * Returns status of the attempt to schedule on the executor. + */ + Status delayUntil(Date_t when); + + /** + * Returns whether the callback is scheduled at all. + */ + bool isActive() const; + + /** + * Returns when the next call to the passed-in callback will be made, or Date_t() if inactive. + */ + Date_t getNextCall() const; + +protected: + void _cancel(WithLock); + Status _scheduleAt(WithLock, Date_t when); + Status _delayUntil(WithLock, Date_t when); + executor::TaskExecutor* _getExecutor() { + return _executor; + } + + mutable Mutex _mutex = MONGO_MAKE_LATCH("DelayableTimeoutCallback"); + +private: + void _handleTimeout(const executor::TaskExecutor::CallbackArgs& cbData); + Status _reschedule(WithLock, Date_t when); + + executor::TaskExecutor* _executor; + executor::TaskExecutor::CallbackHandle _cbHandle; + const executor::TaskExecutor::CallbackFn _callback; + Date_t _nextCall; + + // Timer name is used only for logging. + const std::string _timerName; +}; + +/** + * DelayableTimeoutCallbackWithJitter is a slight variation on DelayableTimeoutCallback + * which adds some additional random time to delays. Since the callback may be delayed at + * intervals much shorter than the random time, this would naively result in the timeout + * either being moved backwards often, or if we forbid moving it backwards, ending up quickly + * moving to the maximum jitter (which isn't very random). To avoid that, we only recompute + * the jitter every maximum jitter interval -- e.g. if the max jitter is 10 seconds and we + * add 3 seconds jitter at time T, we will add 3 seconds jitter to every subsequent call until + * time T + 10. + * + * The typical purpose of the jitter is to prevent two timers receiving delay calls at the same + * times from firing at the same time. + * + * Synchronization of the randomSource is up to the caller; it is provided externally to + * avoid having a separate random number generator per timer. The randomSource function will + * be called with the maximum jitter value passed to delayUntilWithJitter; it should return + * a value in the range [0, maxJitter) or [0, maxJitter] depending on what you want the + * actual jitter range to be. + */ +class DelayableTimeoutCallbackWithJitter : public DelayableTimeoutCallback { +public: + using RandomSource = std::function<int64_t(int64_t)>; + + DelayableTimeoutCallbackWithJitter(executor::TaskExecutor* executor, + executor::TaskExecutor::CallbackFn callback, + RandomSource randomSource, + std::string timerName = std::string()) + : DelayableTimeoutCallback(executor, std::move(callback), timerName), + _randomSource(std::move(randomSource)) {} + + Status scheduleAt(Date_t when); + Status delayUntil(Date_t when); + Status delayUntilWithJitter(Date_t when, Milliseconds maxJitter); + +private: + void _resetRandomization(WithLock); + + RandomSource _randomSource; + Date_t _lastRandomizationTime; + Milliseconds _currentJitter; +}; + +} // namespace repl +} // namespace mongo |