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Make backoff account for already-elapsed time. #1712

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Merged
merged 2 commits into from
Aug 18, 2018
Merged

Make backoff account for already-elapsed time. #1712

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0e4ccc0
Make backoff account for already-elapsed time.
Aug 17, 2018
4d01898
CR Feedback: Guard against nil self.
Aug 18, 2018
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32 changes: 28 additions & 4 deletions Firestore/Source/Remote/FSTExponentialBackoff.mm
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@

#include <random>

#import "Firestore/Source/Util/FSTClasses.h"
#import "Firestore/Source/Util/FSTDispatchQueue.h"

#include "Firestore/core/src/firebase/firestore/util/log.h"
Expand All @@ -33,6 +34,7 @@ @interface FSTExponentialBackoff ()
@property(nonatomic) NSTimeInterval initialDelay;
@property(nonatomic) NSTimeInterval maxDelay;
@property(nonatomic) NSTimeInterval currentBase;
@property(nonatomic) NSTimeInterval lastAttemptTime;
@property(nonatomic, strong, nullable) FSTDelayedCallback *timerCallback;
@end

Expand All @@ -51,6 +53,7 @@ - (instancetype)initWithDispatchQueue:(FSTDispatchQueue *)dispatchQueue
_initialDelay = initialDelay;
_backoffFactor = backoffFactor;
_maxDelay = maxDelay;
_lastAttemptTime = [[NSDate date] timeIntervalSince1970];

[self reset];
}
Expand All @@ -69,13 +72,34 @@ - (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];
NSTimeInterval desiredDelayWithJitter = _currentBase + [self jitterDelay];

// Guard against lastAttemptTime being in the future due to a clock change.
NSTimeInterval delaySoFar = MAX(0, [[NSDate date] timeIntervalSince1970] - self.lastAttemptTime);

// Guard against the backoff delay already being past.
NSTimeInterval remainingDelay = MAX(0, desiredDelayWithJitter - delaySoFar);

if (_currentBase > 0) {
LOG_DEBUG("Backing off for %s seconds (base delay: %s seconds)", delayWithJitter, _currentBase);
LOG_DEBUG(
"Backing off for %s seconds ("
"base delay: %s seconds, "
"delay with jitter: %s seconds, "
"last attempt: %s seconds ago)",
remainingDelay, _currentBase, desiredDelayWithJitter, delaySoFar);
}

self.timerCallback =
[self.dispatchQueue dispatchAfterDelay:delayWithJitter timerID:self.timerID block:block];
FSTWeakify(self);
self.timerCallback = [self.dispatchQueue
dispatchAfterDelay:remainingDelay
timerID:self.timerID
block:^{
FSTStrongify(self);
if (self) {
self.lastAttemptTime = [[NSDate date] timeIntervalSince1970];
block();
}
}];

// Apply backoff factor to determine next delay and ensure it is within bounds.
_currentBase *= _backoffFactor;
Expand Down