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.
23package backoff
24
25import (
26	"time"
27
28	grpcbackoff "google.golang.org/grpc/backoff"
29	"google.golang.org/grpc/internal/grpcrand"
30)
31
32// Strategy defines the methodology for backing off after a grpc connection
33// failure.
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
40// DefaultExponential is an exponential backoff implementation using the
41// default values for all the configurable knobs defined in
42// https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md.
43var DefaultExponential = Exponential{Config: grpcbackoff.DefaultConfig}
44
45// Exponential implements exponential backoff algorithm as defined in
46// https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md.
47type Exponential struct {
48	// Config contains all options to configure the backoff algorithm.
49	Config grpcbackoff.Config
50}
51
52// Backoff returns the amount of time to wait before the next retry given the
53// number of retries.
54func (bc Exponential) Backoff(retries int) time.Duration {
55	if retries == 0 {
56		return bc.Config.BaseDelay
57	}
58	backoff, max := float64(bc.Config.BaseDelay), float64(bc.Config.MaxDelay)
59	for backoff < max && retries > 0 {
60		backoff *= bc.Config.Multiplier
61		retries--
62	}
63	if backoff > max {
64		backoff = max
65	}
66	// Randomize backoff delays so that if a cluster of requests start at
67	// the same time, they won't operate in lockstep.
68	backoff *= 1 + bc.Config.Jitter*(grpcrand.Float64()*2-1)
69	if backoff < 0 {
70		return 0
71	}
72	return time.Duration(backoff)
73}
74