1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
|
/*
* Copyright 2018 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.
*/
#ifndef FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_REMOTE_EXPONENTIAL_BACKOFF_H_
#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_REMOTE_EXPONENTIAL_BACKOFF_H_
#include <chrono> // NOLINT(build/c++11)
#include "Firestore/core/src/firebase/firestore/util/async_queue.h"
#include "Firestore/core/src/firebase/firestore/util/secure_random.h"
namespace firebase {
namespace firestore {
namespace remote {
/**
*
* A helper for running delayed operations following an exponential backoff
* curve between attempts.
*
* The first attempt will be done immediately. After that, each retry will
* have a delay that is made up of a "base" delay which follows the
* exponential backoff curve, and a +/- <=50% "jitter" that is calculated and
* added to the base delay. This prevents clients from accidentally
* synchronizing their delays causing spikes of load to the backend.
*
*/
class ExponentialBackoff {
public:
/**
* @param queue The queue to run operations on.
* @param timer_id The id to use when scheduling backoff operations on the
* queue.
* @param backoff_factor The multiplier to use to determine the extended base
* delay after each attempt.
* @param initial_delay The initial delay (used as the base delay on the first
* retry attempt, that is, the second attempt). Note that jitter will
* still be applied, so the actual delay could be as little as
* `0.5*initial_delay`.
* @param max_delay The maximum base delay after which no further backoff is
* performed. Note that jitter will still be applied, so the actual delay
* could be as much as `1.5*max_delay`.
*/
ExponentialBackoff(util::AsyncQueue* queue,
util::TimerId timer_id,
double backoff_factor,
util::AsyncQueue::Milliseconds initial_delay,
util::AsyncQueue::Milliseconds max_delay);
/**
* Resets the backoff delay.
*
* The very next `backoffAndRun` will have no delay. If it is called again
* (i.e. due to an error), `initial_delay` (plus jitter) will be used, and
* subsequent ones will increase according to the `backoff_factor`.
*/
void Reset() {
current_base_ = Milliseconds{0};
}
/**
* Resets the backoff to the maximum delay (e.g. for use after
* a RESOURCE_EXHAUSTED error).
*/
void ResetToMax() {
current_base_ = max_delay_;
}
/**
* Waits for `current_base` seconds (which may be zero), increases the delay
* and runs the specified operation. If there was a pending operation waiting
* to be run already, it will be canceled.
*/
void BackoffAndRun(util::AsyncQueue::Operation&& operation);
/** Cancels any pending backoff operation scheduled via `BackoffAndRun`. */
void Cancel() {
delayed_operation_.Cancel();
}
private:
using Milliseconds = util::AsyncQueue::Milliseconds;
// Returns a random value in the range [-current_base_/2, current_base_/2].
Milliseconds GetDelayWithJitter();
Milliseconds ClampDelay(Milliseconds delay) const;
util::AsyncQueue* const queue_;
const util::TimerId timer_id_;
util::DelayedOperation delayed_operation_;
const double backoff_factor_;
Milliseconds current_base_{0};
const Milliseconds initial_delay_;
const Milliseconds max_delay_;
util::SecureRandom secure_random_;
};
} // namespace remote
} // namespace firestore
} // namespace firebase
#endif // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_REMOTE_EXPONENTIAL_BACKOFF_H_
|
