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81 lines
2.2 KiB
Go
81 lines
2.2 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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// Package backoff provides a back-off timer type.
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package backoff
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import (
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"context"
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"math/rand/v2"
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"time"
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"tailscale.com/tstime"
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"tailscale.com/types/logger"
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)
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// Backoff tracks state the history of consecutive failures and sleeps
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// an increasing amount of time, up to a provided limit.
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type Backoff struct {
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n int // number of consecutive failures
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maxBackoff time.Duration
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// Name is the name of this backoff timer, for logging purposes.
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name string
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// logf is the function used for log messages when backing off.
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logf logger.Logf
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// tstime.Clock.NewTimer is used instead time.NewTimer.
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Clock tstime.Clock
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// LogLongerThan sets the minimum time of a single backoff interval
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// before we mention it in the log.
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LogLongerThan time.Duration
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}
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// NewBackoff returns a new Backoff timer with the provided name (for logging), logger,
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// and max backoff time. By default, all failures (calls to BackOff with a non-nil err)
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// are logged unless the returned Backoff.LogLongerThan is adjusted.
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func NewBackoff(name string, logf logger.Logf, maxBackoff time.Duration) *Backoff {
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return &Backoff{
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name: name,
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logf: logf,
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maxBackoff: maxBackoff,
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Clock: tstime.StdClock{},
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}
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}
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// BackOff sleeps an increasing amount of time if err is non-nil while the
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// context is active. It resets the backoff schedule once err is nil.
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func (b *Backoff) BackOff(ctx context.Context, err error) {
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if err == nil {
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// No error. Reset number of consecutive failures.
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b.n = 0
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return
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}
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if ctx.Err() != nil {
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// Fast path.
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return
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}
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b.n++
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// n^2 backoff timer is a little smoother than the
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// common choice of 2^n.
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d := time.Duration(b.n*b.n) * 10 * time.Millisecond
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if d > b.maxBackoff {
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d = b.maxBackoff
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}
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// Randomize the delay between 0.5-1.5 x msec, in order
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// to prevent accidental "thundering herd" problems.
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d = time.Duration(float64(d) * (rand.Float64() + 0.5))
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if d >= b.LogLongerThan {
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b.logf("%s: [v1] backoff: %d msec", b.name, d.Milliseconds())
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}
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t, tChannel := b.Clock.NewTimer(d)
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select {
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case <-ctx.Done():
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t.Stop()
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case <-tChannel:
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}
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}
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