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https://github.com/coredns/coredns.git
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bae9514e94
* pkg/up: implement backoff Every 2nd failure we double the interval until we hit 4 * interval. This to have some sort of backoff, esp when a large cluster of coredns shares an upstream (original intent of up package) they will hammer the upstream. This put some back pressure on that. Signed-off-by: Miek Gieben <miek@miek.nl> * Update plugin/pkg/up/up.go Co-Authored-By: miekg <miek@miek.nl>
94 lines
2.0 KiB
Go
94 lines
2.0 KiB
Go
// Package up is used to run a function for some duration. If a new function is added while a previous run is
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// still ongoing, nothing new will be executed.
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package up
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import (
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"sync"
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"time"
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)
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// Probe is used to run a single Func until it returns true (indicating a target is healthy). If an Func
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// is already in progress no new one will be added, i.e. there is always a maximum of 1 checks in flight.
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// When failures start to happen we will back off every second failure up to maximum of 4 intervals.
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type Probe struct {
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sync.Mutex
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inprogress int
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interval time.Duration
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max time.Duration
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}
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// Func is used to determine if a target is alive. If so this function must return nil.
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type Func func() error
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// New returns a pointer to an initialized Probe.
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func New() *Probe { return &Probe{} }
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// Do will probe target, if a probe is already in progress this is a noop.
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func (p *Probe) Do(f Func) {
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p.Lock()
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if p.inprogress != idle {
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p.Unlock()
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return
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}
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p.inprogress = active
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interval := p.interval
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p.Unlock()
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// Passed the lock. Now run f for as long it returns false. If a true is returned
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// we return from the goroutine and we can accept another Func to run.
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go func() {
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i := 1
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for {
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if err := f(); err == nil {
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break
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}
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time.Sleep(interval)
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if i%2 == 0 && i < 4 { // 4 is 2 doubles, so no need to increase anymore - this is *also* checked in double()
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p.double()
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}
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p.Lock()
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if p.inprogress == stop {
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p.Unlock()
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return
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}
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p.Unlock()
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i++
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}
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p.Lock()
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p.inprogress = idle
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p.Unlock()
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}()
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}
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func (p *Probe) double() {
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p.Lock()
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p.interval *= 2
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if p.interval > p.max {
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p.interval = p.max
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}
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p.Unlock()
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}
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// Stop stops the probing.
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func (p *Probe) Stop() {
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p.Lock()
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p.inprogress = stop
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p.Unlock()
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}
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// Start will initialize the probe manager, after which probes can be initiated with Do.
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func (p *Probe) Start(interval time.Duration) {
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p.Lock()
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p.interval = interval
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p.max = interval * multiplier
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p.Unlock()
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}
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const (
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idle = iota
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active
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stop
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multiplier = 4
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)
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