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Some programs use frequent short-duration backoffs even under non-error conditions. They can set this to avoid logging short backoffs when things are operating normally, but still get messages when longer backoffs kick in. Signed-off-by: Avery Pennarun <apenwarr@tailscale.com>
59 lines
1.4 KiB
Go
59 lines
1.4 KiB
Go
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package backoff
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import (
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"context"
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"log"
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"math/rand"
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"time"
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)
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const MAX_BACKOFF_MSEC = 30000
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type Backoff struct {
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n int
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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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// NewTimer is the function that acts like time.NewTimer().
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// You can override this in unit tests.
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NewTimer func(d time.Duration) *time.Timer
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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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func (b *Backoff) BackOff(ctx context.Context, err error) {
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if ctx.Err() == nil && err != nil {
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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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msec := b.n * b.n * 10
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if msec > MAX_BACKOFF_MSEC {
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msec = MAX_BACKOFF_MSEC
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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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msec = rand.Intn(msec) + msec/2
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dur := time.Duration(msec) * time.Millisecond
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if dur >= b.LogLongerThan {
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log.Printf("%s: backoff: %d msec\n", b.Name, msec)
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}
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newTimer := b.NewTimer
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if newTimer == nil {
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newTimer = time.NewTimer
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}
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t := newTimer(dur)
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select {
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case <-ctx.Done():
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t.Stop()
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case <-t.C:
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}
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} else {
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// not a regular error
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b.n = 0
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}
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}
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