1 /*
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.
23 package backoff
24 25 import (
26 "context"
27 "errors"
28 rand "math/rand/v2"
29 "time"
30 31 grpcbackoff "google.golang.org/grpc/backoff"
32 )
33 34 // Strategy defines the methodology for backing off after a grpc connection
35 // failure.
36 type Strategy interface {
37 // Backoff returns the amount of time to wait before the next retry given
38 // the number of consecutive failures.
39 Backoff(retries int) time.Duration
40 }
41 42 // DefaultExponential is an exponential backoff implementation using the
43 // default values for all the configurable knobs defined in
44 // https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md.
45 var DefaultExponential = Exponential{Config: grpcbackoff.DefaultConfig}
46 47 // Exponential implements exponential backoff algorithm as defined in
48 // https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md.
49 type Exponential struct {
50 // Config contains all options to configure the backoff algorithm.
51 Config grpcbackoff.Config
52 }
53 54 // Backoff returns the amount of time to wait before the next retry given the
55 // number of retries.
56 func (bc Exponential) Backoff(retries int) time.Duration {
57 if retries == 0 {
58 return bc.Config.BaseDelay
59 }
60 backoff, max := float64(bc.Config.BaseDelay), float64(bc.Config.MaxDelay)
61 for backoff < max && retries > 0 {
62 backoff *= bc.Config.Multiplier
63 retries--
64 }
65 if backoff > max {
66 backoff = max
67 }
68 // Randomize backoff delays so that if a cluster of requests start at
69 // the same time, they won't operate in lockstep.
70 backoff *= 1 + bc.Config.Jitter*(rand.Float64()*2-1)
71 if backoff < 0 {
72 return 0
73 }
74 return time.Duration(backoff)
75 }
76 77 // ErrResetBackoff is the error to be returned by the function executed by RunF,
78 // to instruct the latter to reset its backoff state.
79 var ErrResetBackoff = errors.New("reset backoff state")
80 81 // RunF provides a convenient way to run a function f repeatedly until the
82 // context expires or f returns a non-nil error that is not ErrResetBackoff.
83 // When f returns ErrResetBackoff, RunF continues to run f, but resets its
84 // backoff state before doing so. backoff accepts an integer representing the
85 // number of retries, and returns the amount of time to backoff.
86 func RunF(ctx context.Context, f func() error, backoff func(int) time.Duration) {
87 attempt := 0
88 timer := time.NewTimer(0)
89 for ctx.Err() == nil {
90 select {
91 case <-timer.C:
92 case <-ctx.Done():
93 timer.Stop()
94 return
95 }
96 97 err := f()
98 if errors.Is(err, ErrResetBackoff) {
99 timer.Reset(0)
100 attempt = 0
101 continue
102 }
103 if err != nil {
104 return
105 }
106 timer.Reset(backoff(attempt))
107 attempt++
108 }
109 }
110