2fe5890d8b
* Fix typos and add todo to fix spelling of dnsutil.MaximumDefaulTTL Signed-off-by: Zhizhen He <hezhizhen.yi@gmail.com>
83 lines
2.2 KiB
Go
83 lines
2.2 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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//
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// There is a tradeoff to be made in figuring out quickly that an upstream is healthy and not doing much work
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// (sending queries) to find that out. Having some kind of exp. backoff here won't help much, because you don't want
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// to backoff too much. You then also need random queries to be performed every so often to quickly detect a working
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// upstream. In the end we just send a query every 0.5 second to check the upstream. This hopefully strikes a balance
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// between getting information about the upstream state quickly and not doing too much work. Note that 0.5s is still an
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// eternity in DNS, so we may actually want to shorten it.
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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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}
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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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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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// 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.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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)
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