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1 // Copyright 2009 The Go Authors. All rights reserved.
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2 // Use of this source code is governed by a BSD-style
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3 // license that can be found in the LICENSE file.
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4
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5 package time
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6
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7 import "errors"
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8
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9 // A Ticker holds a channel that delivers `ticks' of a clock
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10 // at intervals.
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11 type Ticker struct {
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12 C <-chan Time // The channel on which the ticks are delivered.
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13 r runtimeTimer
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14 }
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15
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16 // NewTicker returns a new Ticker containing a channel that will send the
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17 // time with a period specified by the duration argument.
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18 // It adjusts the intervals or drops ticks to make up for slow receivers.
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19 // The duration d must be greater than zero; if not, NewTicker will panic.
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20 // Stop the ticker to release associated resources.
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21 func NewTicker(d Duration) *Ticker {
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22 if d <= 0 {
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23 panic(errors.New("non-positive interval for NewTicker"))
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24 }
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25 // Give the channel a 1-element time buffer.
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26 // If the client falls behind while reading, we drop ticks
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27 // on the floor until the client catches up.
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28 c := make(chan Time, 1)
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29 t := &Ticker{
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30 C: c,
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31 r: runtimeTimer{
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32 when: when(d),
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33 period: int64(d),
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34 f: sendTime,
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35 arg: c,
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36 },
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37 }
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38 startTimer(&t.r)
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39 return t
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40 }
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41
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42 // Stop turns off a ticker. After Stop, no more ticks will be sent.
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131
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43 // Stop does not close the channel, to prevent a concurrent goroutine
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44 // reading from the channel from seeing an erroneous "tick".
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45 func (t *Ticker) Stop() {
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46 stopTimer(&t.r)
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47 }
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48
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49 // Tick is a convenience wrapper for NewTicker providing access to the ticking
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50 // channel only. While Tick is useful for clients that have no need to shut down
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51 // the Ticker, be aware that without a way to shut it down the underlying
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52 // Ticker cannot be recovered by the garbage collector; it "leaks".
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53 // Unlike NewTicker, Tick will return nil if d <= 0.
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54 func Tick(d Duration) <-chan Time {
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55 if d <= 0 {
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56 return nil
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57 }
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58 return NewTicker(d).C
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59 }
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