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127 lines
2.5 KiB
127 lines
2.5 KiB
package common
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import (
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"time"
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)
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/*
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ThrottleTimer fires an event at most "dur" after each .Set() call.
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If a short burst of .Set() calls happens, ThrottleTimer fires once.
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If a long continuous burst of .Set() calls happens, ThrottleTimer fires
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at most once every "dur".
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*/
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type ThrottleTimer struct {
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Name string
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Ch <-chan struct{}
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input chan command
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output chan<- struct{}
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dur time.Duration
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timer *time.Timer
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isSet bool
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}
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type command int32
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const (
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Set command = iota
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Unset
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Quit
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)
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// NewThrottleTimer creates a new ThrottleTimer.
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func NewThrottleTimer(name string, dur time.Duration) *ThrottleTimer {
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c := make(chan struct{})
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var t = &ThrottleTimer{
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Name: name,
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Ch: c,
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dur: dur,
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input: make(chan command),
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output: c,
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timer: time.NewTimer(dur),
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}
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t.timer.Stop()
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go t.run()
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return t
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}
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func (t *ThrottleTimer) run() {
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for {
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select {
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case cmd := <-t.input:
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// stop goroutine if the input says so
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// don't close channels, as closed channels mess up select reads
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if t.processInput(cmd) {
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return
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}
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case <-t.timer.C:
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t.trySend()
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}
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}
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}
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// trySend performs non-blocking send on t.Ch
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func (t *ThrottleTimer) trySend() {
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select {
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case t.output <- struct{}{}:
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t.isSet = false
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default:
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// if we just want to drop, replace this with t.isSet = false
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t.timer.Reset(t.dur)
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}
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}
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// all modifications of the internal state of ThrottleTimer
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// happen in this method. It is only called from the run goroutine
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// so we avoid any race conditions
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func (t *ThrottleTimer) processInput(cmd command) (shutdown bool) {
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switch cmd {
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case Set:
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if !t.isSet {
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t.isSet = true
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t.timer.Reset(t.dur)
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}
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case Quit:
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shutdown = true
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fallthrough
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case Unset:
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if t.isSet {
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t.isSet = false
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t.timer.Stop()
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}
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default:
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panic("unknown command!")
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}
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return shutdown
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}
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func (t *ThrottleTimer) Set() {
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t.input <- Set
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}
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func (t *ThrottleTimer) Unset() {
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t.input <- Unset
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}
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// Stop prevents the ThrottleTimer from firing. It always returns true. Stop does not
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// close the channel, to prevent a read from the channel succeeding
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// incorrectly.
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//
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// To prevent a timer created with NewThrottleTimer from firing after a call to
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// Stop, check the return value and drain the channel.
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//
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// For example, assuming the program has not received from t.C already:
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//
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// if !t.Stop() {
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// <-t.C
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// }
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//
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// For ease of stopping services before starting them, we ignore Stop on nil
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// ThrottleTimers.
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func (t *ThrottleTimer) Stop() bool {
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if t == nil {
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return false
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}
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t.input <- Quit
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return true
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}
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