Black Lives Matter. Support the Equal Justice Initiative.

Source file src/time/sleep.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  // Sleep pauses the current goroutine for at least the duration d.
     8  // A negative or zero duration causes Sleep to return immediately.
     9  func Sleep(d Duration)
    10  
    11  // Interface to timers implemented in package runtime.
    12  // Must be in sync with ../runtime/time.go:/^type timer
    13  type runtimeTimer struct {
    14  	pp       uintptr
    15  	when     int64
    16  	period   int64
    17  	f        func(interface{}, uintptr) // NOTE: must not be closure
    18  	arg      interface{}
    19  	seq      uintptr
    20  	nextwhen int64
    21  	status   uint32
    22  }
    23  
    24  // when is a helper function for setting the 'when' field of a runtimeTimer.
    25  // It returns what the time will be, in nanoseconds, Duration d in the future.
    26  // If d is negative, it is ignored. If the returned value would be less than
    27  // zero because of an overflow, MaxInt64 is returned.
    28  func when(d Duration) int64 {
    29  	if d <= 0 {
    30  		return runtimeNano()
    31  	}
    32  	t := runtimeNano() + int64(d)
    33  	if t < 0 {
    34  		t = 1<<63 - 1 // math.MaxInt64
    35  	}
    36  	return t
    37  }
    38  
    39  func startTimer(*runtimeTimer)
    40  func stopTimer(*runtimeTimer) bool
    41  func resetTimer(*runtimeTimer, int64)
    42  
    43  // The Timer type represents a single event.
    44  // When the Timer expires, the current time will be sent on C,
    45  // unless the Timer was created by AfterFunc.
    46  // A Timer must be created with NewTimer or AfterFunc.
    47  type Timer struct {
    48  	C <-chan Time
    49  	r runtimeTimer
    50  }
    51  
    52  // Stop prevents the Timer from firing.
    53  // It returns true if the call stops the timer, false if the timer has already
    54  // expired or been stopped.
    55  // Stop does not close the channel, to prevent a read from the channel succeeding
    56  // incorrectly.
    57  //
    58  // To ensure the channel is empty after a call to Stop, check the
    59  // return value and drain the channel.
    60  // For example, assuming the program has not received from t.C already:
    61  //
    62  // 	if !t.Stop() {
    63  // 		<-t.C
    64  // 	}
    65  //
    66  // This cannot be done concurrent to other receives from the Timer's
    67  // channel or other calls to the Timer's Stop method.
    68  //
    69  // For a timer created with AfterFunc(d, f), if t.Stop returns false, then the timer
    70  // has already expired and the function f has been started in its own goroutine;
    71  // Stop does not wait for f to complete before returning.
    72  // If the caller needs to know whether f is completed, it must coordinate
    73  // with f explicitly.
    74  func (t *Timer) Stop() bool {
    75  	if t.r.f == nil {
    76  		panic("time: Stop called on uninitialized Timer")
    77  	}
    78  	return stopTimer(&t.r)
    79  }
    80  
    81  // NewTimer creates a new Timer that will send
    82  // the current time on its channel after at least duration d.
    83  func NewTimer(d Duration) *Timer {
    84  	c := make(chan Time, 1)
    85  	t := &Timer{
    86  		C: c,
    87  		r: runtimeTimer{
    88  			when: when(d),
    89  			f:    sendTime,
    90  			arg:  c,
    91  		},
    92  	}
    93  	startTimer(&t.r)
    94  	return t
    95  }
    96  
    97  // Reset changes the timer to expire after duration d.
    98  // It returns true if the timer had been active, false if the timer had
    99  // expired or been stopped.
   100  //
   101  // Reset should be invoked only on stopped or expired timers with drained channels.
   102  // If a program has already received a value from t.C, the timer is known
   103  // to have expired and the channel drained, so t.Reset can be used directly.
   104  // If a program has not yet received a value from t.C, however,
   105  // the timer must be stopped and—if Stop reports that the timer expired
   106  // before being stopped—the channel explicitly drained:
   107  //
   108  // 	if !t.Stop() {
   109  // 		<-t.C
   110  // 	}
   111  // 	t.Reset(d)
   112  //
   113  // This should not be done concurrent to other receives from the Timer's
   114  // channel.
   115  //
   116  // Note that it is not possible to use Reset's return value correctly, as there
   117  // is a race condition between draining the channel and the new timer expiring.
   118  // Reset should always be invoked on stopped or expired channels, as described above.
   119  // The return value exists to preserve compatibility with existing programs.
   120  func (t *Timer) Reset(d Duration) bool {
   121  	if t.r.f == nil {
   122  		panic("time: Reset called on uninitialized Timer")
   123  	}
   124  	w := when(d)
   125  	active := stopTimer(&t.r)
   126  	resetTimer(&t.r, w)
   127  	return active
   128  }
   129  
   130  func sendTime(c interface{}, seq uintptr) {
   131  	// Non-blocking send of time on c.
   132  	// Used in NewTimer, it cannot block anyway (buffer).
   133  	// Used in NewTicker, dropping sends on the floor is
   134  	// the desired behavior when the reader gets behind,
   135  	// because the sends are periodic.
   136  	select {
   137  	case c.(chan Time) <- Now():
   138  	default:
   139  	}
   140  }
   141  
   142  // After waits for the duration to elapse and then sends the current time
   143  // on the returned channel.
   144  // It is equivalent to NewTimer(d).C.
   145  // The underlying Timer is not recovered by the garbage collector
   146  // until the timer fires. If efficiency is a concern, use NewTimer
   147  // instead and call Timer.Stop if the timer is no longer needed.
   148  func After(d Duration) <-chan Time {
   149  	return NewTimer(d).C
   150  }
   151  
   152  // AfterFunc waits for the duration to elapse and then calls f
   153  // in its own goroutine. It returns a Timer that can
   154  // be used to cancel the call using its Stop method.
   155  func AfterFunc(d Duration, f func()) *Timer {
   156  	t := &Timer{
   157  		r: runtimeTimer{
   158  			when: when(d),
   159  			f:    goFunc,
   160  			arg:  f,
   161  		},
   162  	}
   163  	startTimer(&t.r)
   164  	return t
   165  }
   166  
   167  func goFunc(arg interface{}, seq uintptr) {
   168  	go arg.(func())()
   169  }
   170  

View as plain text