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Source file src/time/tick.go

Documentation: time

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package time
     6  
     7  import "errors"
     8  
     9  // A Ticker holds a channel that delivers `ticks' of a clock
    10  // at intervals.
    11  type Ticker struct {
    12  	C <-chan Time // The channel on which the ticks are delivered.
    13  	r runtimeTimer
    14  }
    15  
    16  // NewTicker returns a new Ticker containing a channel that will send the
    17  // time with a period specified by the duration argument.
    18  // It adjusts the intervals or drops ticks to make up for slow receivers.
    19  // The duration d must be greater than zero; if not, NewTicker will panic.
    20  // Stop the ticker to release associated resources.
    21  func NewTicker(d Duration) *Ticker {
    22  	if d <= 0 {
    23  		panic(errors.New("non-positive interval for NewTicker"))
    24  	}
    25  	// Give the channel a 1-element time buffer.
    26  	// If the client falls behind while reading, we drop ticks
    27  	// on the floor until the client catches up.
    28  	c := make(chan Time, 1)
    29  	t := &Ticker{
    30  		C: c,
    31  		r: runtimeTimer{
    32  			when:   when(d),
    33  			period: int64(d),
    34  			f:      sendTime,
    35  			arg:    c,
    36  		},
    37  	}
    38  	startTimer(&t.r)
    39  	return t
    40  }
    41  
    42  // Stop turns off a ticker. After Stop, no more ticks will be sent.
    43  // Stop does not close the channel, to prevent a read from the channel succeeding
    44  // incorrectly.
    45  func (t *Ticker) Stop() {
    46  	stopTimer(&t.r)
    47  }
    48  
    49  // Tick is a convenience wrapper for NewTicker providing access to the ticking
    50  // channel only. While Tick is useful for clients that have no need to shut down
    51  // the Ticker, be aware that without a way to shut it down the underlying
    52  // Ticker cannot be recovered by the garbage collector; it "leaks".
    53  // Unlike NewTicker, Tick will return nil if d <= 0.
    54  func Tick(d Duration) <-chan Time {
    55  	if d <= 0 {
    56  		return nil
    57  	}
    58  	return NewTicker(d).C
    59  }
    60  

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