mirror of
https://github.com/firebase/firebase-ios-sdk
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85 lines
3.1 KiB
Objective-C
85 lines
3.1 KiB
Objective-C
/*
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* Copyright 2017 Google
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#import <Foundation/Foundation.h>
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#import "Firestore/Source/Util/FSTDispatchQueue.h"
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NS_ASSUME_NONNULL_BEGIN
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/**
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* Helper to implement exponential backoff.
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*
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* In general, call -reset after each successful round-trip. Call -backoffAndRunBlock before
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* retrying after an error. Each backoffAndRunBlock will increase the delay between retries.
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*/
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@interface FSTExponentialBackoff : NSObject
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/**
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* Initializes a helper for running delayed tasks following an exponential backoff curve
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* between attempts.
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*
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* Each delay is made up of a "base" delay which follows the exponential backoff curve, and a
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* +/- 50% "jitter" that is calculated and added to the base delay. This prevents clients from
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* accidentally synchronizing their delays causing spikes of load to the backend.
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*
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* @param dispatchQueue The dispatch queue to run tasks on.
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* @param timerID The ID to use when scheduling backoff operations on the FSTDispatchQueue.
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* @param initialDelay The initial delay (used as the base delay on the first retry attempt).
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* Note that jitter will still be applied, so the actual delay could be as little as
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* 0.5*initialDelay.
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* @param backoffFactor The multiplier to use to determine the extended base delay after each
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* attempt.
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* @param maxDelay The maximum base delay after which no further backoff is performed. Note that
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* jitter will still be applied, so the actual delay could be as much as 1.5*maxDelay.
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*/
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- (instancetype)initWithDispatchQueue:(FSTDispatchQueue *)dispatchQueue
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timerID:(FSTTimerID)timerID
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initialDelay:(NSTimeInterval)initialDelay
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backoffFactor:(double)backoffFactor
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maxDelay:(NSTimeInterval)maxDelay NS_DESIGNATED_INITIALIZER;
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- (instancetype)init NS_UNAVAILABLE;
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/**
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* Resets the backoff delay.
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*
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* The very next backoffAndRunBlock: will have no delay. If it is called again (i.e. due to an
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* error), initialDelay (plus jitter) will be used, and subsequent ones will increase according
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* to the backoffFactor.
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*/
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- (void)reset;
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/**
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* Resets the backoff to the maximum delay (e.g. for use after a RESOURCE_EXHAUSTED error).
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*/
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- (void)resetToMax;
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/**
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* Waits for currentDelay seconds, increases the delay and runs the specified block. If there was
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* a pending block waiting to be run already, it will be canceled.
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*
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* @param block The block to run.
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*/
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- (void)backoffAndRunBlock:(void (^)(void))block;
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/** Cancels any pending backoff block scheduled via backoffAndRunBlock:. */
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- (void)cancel;
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@end
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NS_ASSUME_NONNULL_END
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