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Source file src/time/sleep.go

     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	// runtimeNano returns the current value of the runtime clock in nanoseconds.
    12	func runtimeNano() int64
    13	
    14	// Interface to timers implemented in package runtime.
    15	// Must be in sync with ../runtime/runtime.h:/^struct.Timer$
    16	type runtimeTimer struct {
    17		i      int
    18		when   int64
    19		period int64
    20		f      func(interface{}, uintptr) // NOTE: must not be closure
    21		arg    interface{}
    22		seq    uintptr
    23	}
    24	
    25	// when is a helper function for setting the 'when' field of a runtimeTimer.
    26	// It returns what the time will be, in nanoseconds, Duration d in the future.
    27	// If d is negative, it is ignored. If the returned value would be less than
    28	// zero because of an overflow, MaxInt64 is returned.
    29	func when(d Duration) int64 {
    30		if d <= 0 {
    31			return runtimeNano()
    32		}
    33		t := runtimeNano() + int64(d)
    34		if t < 0 {
    35			t = 1<<63 - 1 // math.MaxInt64
    36		}
    37		return t
    38	}
    39	
    40	func startTimer(*runtimeTimer)
    41	func stopTimer(*runtimeTimer) bool
    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 prevent the timer firing after a call to Stop,
    59	// check the return value and drain the channel. For example:
    60	// 	if !t.Stop() {
    61	// 		<-t.C
    62	// 	}
    63	// This cannot be done concurrent to other receives from the Timer's
    64	// channel.
    65	func (t *Timer) Stop() bool {
    66		if t.r.f == nil {
    67			panic("time: Stop called on uninitialized Timer")
    68		}
    69		return stopTimer(&t.r)
    70	}
    71	
    72	// NewTimer creates a new Timer that will send
    73	// the current time on its channel after at least duration d.
    74	func NewTimer(d Duration) *Timer {
    75		c := make(chan Time, 1)
    76		t := &Timer{
    77			C: c,
    78			r: runtimeTimer{
    79				when: when(d),
    80				f:    sendTime,
    81				arg:  c,
    82			},
    83		}
    84		startTimer(&t.r)
    85		return t
    86	}
    87	
    88	// Reset changes the timer to expire after duration d.
    89	// It returns true if the timer had been active, false if the timer had
    90	// expired or been stopped.
    91	//
    92	// To reuse an active timer, always call its Stop method first and—if it had
    93	// expired—drain the value from its channel. For example:
    94	// 	if !t.Stop() {
    95	// 		<-t.C
    96	// 	}
    97	// 	t.Reset(d)
    98	// This should not be done concurrent to other receives from the Timer's
    99	// channel.
   100	//
   101	// Note that it is not possible to use Reset's return value correctly, as there
   102	// is a race condition between draining the channel and the new timer expiring.
   103	// Reset should always be used in concert with Stop, as described above.
   104	// The return value exists to preserve compatibility with existing programs.
   105	func (t *Timer) Reset(d Duration) bool {
   106		if t.r.f == nil {
   107			panic("time: Reset called on uninitialized Timer")
   108		}
   109		w := when(d)
   110		active := stopTimer(&t.r)
   111		t.r.when = w
   112		startTimer(&t.r)
   113		return active
   114	}
   115	
   116	func sendTime(c interface{}, seq uintptr) {
   117		// Non-blocking send of time on c.
   118		// Used in NewTimer, it cannot block anyway (buffer).
   119		// Used in NewTicker, dropping sends on the floor is
   120		// the desired behavior when the reader gets behind,
   121		// because the sends are periodic.
   122		select {
   123		case c.(chan Time) <- Now():
   124		default:
   125		}
   126	}
   127	
   128	// After waits for the duration to elapse and then sends the current time
   129	// on the returned channel.
   130	// It is equivalent to NewTimer(d).C.
   131	// The underlying Timer is not recovered by the garbage collector
   132	// until the timer fires. If efficiency is a concern, use NewTimer
   133	// instead and call Timer.Stop if the timer is no longer needed.
   134	func After(d Duration) <-chan Time {
   135		return NewTimer(d).C
   136	}
   137	
   138	// AfterFunc waits for the duration to elapse and then calls f
   139	// in its own goroutine. It returns a Timer that can
   140	// be used to cancel the call using its Stop method.
   141	func AfterFunc(d Duration, f func()) *Timer {
   142		t := &Timer{
   143			r: runtimeTimer{
   144				when: when(d),
   145				f:    goFunc,
   146				arg:  f,
   147			},
   148		}
   149		startTimer(&t.r)
   150		return t
   151	}
   152	
   153	func goFunc(arg interface{}, seq uintptr) {
   154		go arg.(func())()
   155	}
   156	

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