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 "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} 79