cloudflare/cloudflared
Publicmirrored from https://github.com/cloudflare/cloudflaredAvailable
origin/backoffhandler.go
95lines · modeblame
d06fc520Areg Harutyunyan8 years ago | 1 | package origin |
| 2 | | |
| 3 | import ( | |
| 4 | "time" | |
| 5 | | |
| 6 | "golang.org/x/net/context" | |
| 7 | ) | |
| 8 | | |
| 9 | // Redeclare time functions so they can be overridden in tests. | |
| 10 | var ( | |
| 11 | timeNow = time.Now | |
| 12 | timeAfter = time.After | |
| 13 | ) | |
| 14 | | |
| 15 | // BackoffHandler manages exponential backoff and limits the maximum number of retries. | |
| 16 | // The base time period is 1 second, doubling with each retry. | |
| 17 | // After initial success, a grace period can be set to reset the backoff timer if | |
| 18 | // a connection is maintained successfully for a long enough period. The base grace period | |
| 19 | // is 2 seconds, doubling with each retry. | |
| 20 | type BackoffHandler struct { | |
| 21 | // MaxRetries sets the maximum number of retries to perform. The default value | |
| 22 | // of 0 disables retry completely. | |
| 23 | MaxRetries uint | |
| 24 | // RetryForever caps the exponential backoff period according to MaxRetries | |
| 25 | // but allows you to retry indefinitely. | |
| 26 | RetryForever bool | |
| 27 | // BaseTime sets the initial backoff period. | |
| 28 | BaseTime time.Duration | |
| 29 | | |
| 30 | retries uint | |
| 31 | resetDeadline time.Time | |
| 32 | } | |
| 33 | | |
| 34 | func (b BackoffHandler) GetBackoffDuration(ctx context.Context) (time.Duration, bool) { | |
| 35 | // Follows the same logic as Backoff, but without mutating the receiver. | |
| 36 | // This select has to happen first to reflect the actual behaviour of the Backoff function. | |
| 37 | select { | |
| 38 | case <-ctx.Done(): | |
| 39 | return time.Duration(0), false | |
| 40 | default: | |
| 41 | } | |
| 42 | if !b.resetDeadline.IsZero() && timeNow().After(b.resetDeadline) { | |
| 43 | // b.retries would be set to 0 at this point | |
| 44 | return time.Second, true | |
| 45 | } | |
| 46 | if b.retries >= b.MaxRetries && !b.RetryForever { | |
| 47 | return time.Duration(0), false | |
| 48 | } | |
| 49 | return time.Duration(b.GetBaseTime() * 1 << b.retries), true | |
| 50 | } | |
| 51 | | |
| 52 | // BackoffTimer returns a channel that sends the current time when the exponential backoff timeout expires. | |
| 53 | // Returns nil if the maximum number of retries have been used. | |
| 54 | func (b *BackoffHandler) BackoffTimer() <-chan time.Time { | |
| 55 | if !b.resetDeadline.IsZero() && timeNow().After(b.resetDeadline) { | |
| 56 | b.retries = 0 | |
| 57 | b.resetDeadline = time.Time{} | |
| 58 | } | |
| 59 | if b.retries >= b.MaxRetries { | |
| 60 | if !b.RetryForever { | |
| 61 | return nil | |
| 62 | } | |
| 63 | } else { | |
| 64 | b.retries++ | |
| 65 | } | |
| 66 | return timeAfter(time.Duration(b.GetBaseTime() * 1 << (b.retries - 1))) | |
| 67 | } | |
| 68 | | |
| 69 | // Backoff is used to wait according to exponential backoff. Returns false if the | |
| 70 | // maximum number of retries have been used or if the underlying context has been cancelled. | |
| 71 | func (b *BackoffHandler) Backoff(ctx context.Context) bool { | |
| 72 | c := b.BackoffTimer() | |
| 73 | if c == nil { | |
| 74 | return false | |
| 75 | } | |
| 76 | select { | |
| 77 | case <-c: | |
| 78 | return true | |
| 79 | case <-ctx.Done(): | |
| 80 | return false | |
| 81 | } | |
| 82 | } | |
| 83 | | |
| 84 | // Sets a grace period within which the the backoff timer is maintained. After the grace | |
| 85 | // period expires, the number of retries & backoff duration is reset. | |
| 86 | func (b *BackoffHandler) SetGracePeriod() { | |
| 87 | b.resetDeadline = timeNow().Add(time.Duration(b.GetBaseTime() * 2 << b.retries)) | |
| 88 | } | |
| 89 | | |
| 90 | func (b BackoffHandler) GetBaseTime() time.Duration { | |
| 91 | if b.BaseTime == 0 { | |
| 92 | return time.Second | |
| 93 | } | |
| 94 | return b.BaseTime | |
| 95 | } |