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/*
* Copyright 2017 Google
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#import "Firestore/Source/Remote/FSTExponentialBackoff.h"
#include <random>
#import "Firestore/Source/Util/FSTDispatchQueue.h"
#include "Firestore/core/src/firebase/firestore/util/log.h"
#include "Firestore/core/src/firebase/firestore/util/secure_random.h"
using firebase::firestore::util::SecureRandom;
@interface FSTExponentialBackoff ()
@property(nonatomic, strong) FSTDispatchQueue *dispatchQueue;
@property(nonatomic, assign, readonly) FSTTimerID timerID;
@property(nonatomic) double backoffFactor;
@property(nonatomic) NSTimeInterval initialDelay;
@property(nonatomic) NSTimeInterval maxDelay;
@property(nonatomic) NSTimeInterval currentBase;
@property(nonatomic, strong, nullable) FSTDelayedCallback *timerCallback;
@end
@implementation FSTExponentialBackoff {
SecureRandom _secureRandom;
}
- (instancetype)initWithDispatchQueue:(FSTDispatchQueue *)dispatchQueue
timerID:(FSTTimerID)timerID
initialDelay:(NSTimeInterval)initialDelay
backoffFactor:(double)backoffFactor
maxDelay:(NSTimeInterval)maxDelay {
if (self = [super init]) {
_dispatchQueue = dispatchQueue;
_timerID = timerID;
_initialDelay = initialDelay;
_backoffFactor = backoffFactor;
_maxDelay = maxDelay;
[self reset];
}
return self;
}
- (void)reset {
_currentBase = 0;
}
- (void)resetToMax {
_currentBase = _maxDelay;
}
- (void)backoffAndRunBlock:(void (^)(void))block {
[self cancel];
// First schedule the block using the current base (which may be 0 and should be honored as such).
NSTimeInterval delayWithJitter = _currentBase + [self jitterDelay];
if (_currentBase > 0) {
LOG_DEBUG("Backing off for %s seconds (base delay: %s seconds)", delayWithJitter, _currentBase);
}
self.timerCallback =
[self.dispatchQueue dispatchAfterDelay:delayWithJitter timerID:self.timerID block:block];
// Apply backoff factor to determine next delay and ensure it is within bounds.
_currentBase *= _backoffFactor;
if (_currentBase < _initialDelay) {
_currentBase = _initialDelay;
}
if (_currentBase > _maxDelay) {
_currentBase = _maxDelay;
}
}
- (void)cancel {
if (self.timerCallback) {
[self.timerCallback cancel];
self.timerCallback = nil;
}
}
/** Returns a random value in the range [-currentBase/2, currentBase/2] */
- (NSTimeInterval)jitterDelay {
std::uniform_real_distribution<double> dist;
double random_double = dist(_secureRandom);
return (random_double - 0.5) * _currentBase;
}
@end
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