1 files changed, 177 insertions, 0 deletions
diff --git a/src/pkg/time/sleep.go b/src/pkg/time/sleep.go
new file mode 100644
index 000000000..314622d0d
--- /dev/null
+++ b/src/pkg/time/sleep.go
@@ -0,0 +1,177 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package time
+
+import (
+	"container/heap"
+	"sync"
+)
+
+// The Timer type represents a single event.
+// When the Timer expires, the current time will be sent on C
+// unless the Timer represents an AfterFunc event.
+type Timer struct {
+	C <-chan int64
+	t int64       // The absolute time that the event should fire.
+	f func(int64) // The function to call when the event fires.
+	i int         // The event's index inside eventHeap.
+}
+
+type timerHeap []*Timer
+
+// forever is the absolute time (in ns) of an event that is forever away.
+const forever = 1 << 62
+
+// maxSleepTime is the maximum length of time that a sleeper
+// sleeps for before checking if it is defunct.
+const maxSleepTime = 1e9
+
+var (
+	// timerMutex guards the variables inside this var group.
+	timerMutex sync.Mutex
+
+	// timers holds a binary heap of pending events, terminated with a sentinel.
+	timers timerHeap
+
+	// currentSleeper is an ever-incrementing counter which represents
+	// the current sleeper. It allows older sleepers to detect that they are
+	// defunct and exit.
+	currentSleeper int64
+)
+
+func init() {
+	timers.Push(&Timer{t: forever}) // sentinel
+}
+
+// NewTimer creates a new Timer that will send
+// the current time on its channel after at least ns nanoseconds.
+func NewTimer(ns int64) *Timer {
+	c := make(chan int64, 1)
+	e := after(ns, func(t int64) { c <- t })
+	e.C = c
+	return e
+}
+
+// After waits at least ns nanoseconds before sending the current time
+// on the returned channel.
+// It is equivalent to NewTimer(ns).C.
+func After(ns int64) <-chan int64 {
+	return NewTimer(ns).C
+}
+
+// AfterFunc waits at least ns nanoseconds before calling f
+// in its own goroutine. It returns a Timer that can
+// be used to cancel the call using its Stop method.
+func AfterFunc(ns int64, f func()) *Timer {
+	return after(ns, func(_ int64) {
+		go f()
+	})
+}
+
+// Stop prevents the Timer from firing.
+// It returns true if the call stops the timer, false if the timer has already
+// expired or stopped.
+func (e *Timer) Stop() (ok bool) {
+	timerMutex.Lock()
+	// Avoid removing the first event in the queue so that
+	// we don't start a new sleeper unnecessarily.
+	if e.i > 0 {
+		heap.Remove(timers, e.i)
+	}
+	ok = e.f != nil
+	e.f = nil
+	timerMutex.Unlock()
+	return
+}
+
+// after is the implementation of After and AfterFunc.
+// When the current time is after ns, it calls f with the current time.
+// It assumes that f will not block.
+func after(ns int64, f func(int64)) (e *Timer) {
+	now := Nanoseconds()
+	t := now + ns
+	if ns > 0 && t < now {
+		panic("time: time overflow")
+	}
+	timerMutex.Lock()
+	t0 := timers[0].t
+	e = &Timer{nil, t, f, -1}
+	heap.Push(timers, e)
+	// Start a new sleeper if the new event is before
+	// the first event in the queue. If the length of time
+	// until the new event is at least maxSleepTime,
+	// then we're guaranteed that the sleeper will wake up
+	// in time to service it, so no new sleeper is needed.
+	if t0 > t && (t0 == forever || ns < maxSleepTime) {
+		currentSleeper++
+		go sleeper(currentSleeper)
+	}
+	timerMutex.Unlock()
+	return
+}
+
+// sleeper continually looks at the earliest event in the queue, waits until it happens,
+// then removes any events in the queue that are due. It stops when the queue
+// is empty or when another sleeper has been started.
+func sleeper(sleeperId int64) {
+	timerMutex.Lock()
+	e := timers[0]
+	t := Nanoseconds()
+	for e.t != forever {
+		if dt := e.t - t; dt > 0 {
+			if dt > maxSleepTime {
+				dt = maxSleepTime
+			}
+			timerMutex.Unlock()
+			sysSleep(dt)
+			timerMutex.Lock()
+			if currentSleeper != sleeperId {
+				// Another sleeper has been started, making this one redundant.
+				break
+			}
+		}
+		e = timers[0]
+		t = Nanoseconds()
+		for t >= e.t {
+			if e.f != nil {
+				e.f(t)
+				e.f = nil
+			}
+			heap.Pop(timers)
+			e = timers[0]
+		}
+	}
+	timerMutex.Unlock()
+}
+
+func (timerHeap) Len() int {
+	return len(timers)
+}
+
+func (timerHeap) Less(i, j int) bool {
+	return timers[i].t < timers[j].t
+}
+
+func (timerHeap) Swap(i, j int) {
+	timers[i], timers[j] = timers[j], timers[i]
+	timers[i].i = i
+	timers[j].i = j
+}
+
+func (timerHeap) Push(x interface{}) {
+	e := x.(*Timer)
+	e.i = len(timers)
+	timers = append(timers, e)
+}
+
+func (timerHeap) Pop() interface{} {
+	// TODO: possibly shrink array.
+	n := len(timers) - 1
+	e := timers[n]
+	timers[n] = nil
+	timers = timers[0:n]
+	e.i = -1
+	return e
+}