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Matteo Scandoloa6a3aee2019-11-26 13:30:14 -07001/*
2 *
3 * Copyright 2017 gRPC authors.
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 *
17 */
18
19// Package backoff implement the backoff strategy for gRPC.
20//
21// This is kept in internal until the gRPC project decides whether or not to
22// allow alternative backoff strategies.
23package backoff
24
25import (
26 "time"
27
28 "google.golang.org/grpc/internal/grpcrand"
29)
30
31// Strategy defines the methodology for backing off after a grpc connection
32// failure.
33//
34type Strategy interface {
35 // Backoff returns the amount of time to wait before the next retry given
36 // the number of consecutive failures.
37 Backoff(retries int) time.Duration
38}
39
40const (
41 // baseDelay is the amount of time to wait before retrying after the first
42 // failure.
43 baseDelay = 1.0 * time.Second
44 // factor is applied to the backoff after each retry.
45 factor = 1.6
46 // jitter provides a range to randomize backoff delays.
47 jitter = 0.2
48)
49
50// Exponential implements exponential backoff algorithm as defined in
51// https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md.
52type Exponential struct {
53 // MaxDelay is the upper bound of backoff delay.
54 MaxDelay time.Duration
55}
56
57// Backoff returns the amount of time to wait before the next retry given the
58// number of retries.
59func (bc Exponential) Backoff(retries int) time.Duration {
60 if retries == 0 {
61 return baseDelay
62 }
63 backoff, max := float64(baseDelay), float64(bc.MaxDelay)
64 for backoff < max && retries > 0 {
65 backoff *= factor
66 retries--
67 }
68 if backoff > max {
69 backoff = max
70 }
71 // Randomize backoff delays so that if a cluster of requests start at
72 // the same time, they won't operate in lockstep.
73 backoff *= 1 + jitter*(grpcrand.Float64()*2-1)
74 if backoff < 0 {
75 return 0
76 }
77 return time.Duration(backoff)
78}