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package clock
import (
"context"
"sync"
"time"
)
type action interface {
// Return true if the action is due to fire
isDue(time.Time) bool
// fire triggers the action. Returns true if the action needs to fire again in the future
fire(time.Time) bool
}
type task struct {
ch chan time.Time
due time.Time
}
func (t task) isDue(now time.Time) bool {
return !t.due.After(now)
}
func (t task) fire(now time.Time) bool {
t.ch <- now
close(t.ch)
return false
}
type ticker struct {
c Clock
ch chan time.Time
nextDue time.Time
period time.Duration
stopped bool
sync.Mutex
}
func (t *ticker) Ch() <-chan time.Time {
return t.ch
}
func (t *ticker) Stop() {
t.Lock()
defer t.Unlock()
t.stopped = true
}
func (t *ticker) Reset(d time.Duration) {
if d <= 0 {
panic("Continuously firing tickers are a really bad idea")
}
t.Lock()
defer t.Unlock()
t.period = d
t.nextDue = t.c.Now().Add(d)
}
func (t *ticker) isDue(now time.Time) bool {
t.Lock()
defer t.Unlock()
return !t.nextDue.After(now)
}
func (t *ticker) fire(now time.Time) bool {
t.Lock()
defer t.Unlock()
if t.stopped {
return false
}
t.ch <- now
t.nextDue = now.Add(t.period)
return true
}
type DeterministicClock struct {
now time.Time
pending []action
newPendingCh chan struct{}
lock sync.Mutex
}
// NewDeterministicClock creates a new clock where time only advances when the DeterministicClock.AdvanceTime method is called.
// This is intended for use in situations where a deterministic clock is required, such as testing or event driven systems.
func NewDeterministicClock(now time.Time) *DeterministicClock {
return &DeterministicClock{
now: now,
newPendingCh: make(chan struct{}, 1),
}
}
func (s *DeterministicClock) Now() time.Time {
s.lock.Lock()
defer s.lock.Unlock()
return s.now
}
func (s *DeterministicClock) After(d time.Duration) <-chan time.Time {
s.lock.Lock()
defer s.lock.Unlock()
ch := make(chan time.Time, 1)
if d.Nanoseconds() == 0 {
ch <- s.now
close(ch)
} else {
s.addPending(&task{ch: ch, due: s.now.Add(d)})
}
return ch
}
func (s *DeterministicClock) NewTicker(d time.Duration) Ticker {
if d <= 0 {
panic("Continuously firing tickers are a really bad idea")
}
s.lock.Lock()
defer s.lock.Unlock()
ch := make(chan time.Time, 1)
t := &ticker{
c: s,
ch: ch,
nextDue: s.now.Add(d),
period: d,
}
s.addPending(t)
return t
}
func (s *DeterministicClock) addPending(t action) {
s.pending = append(s.pending, t)
select {
case s.newPendingCh <- struct{}{}:
default:
// Must already have a new pending task flagged, do nothing
}
}
func (s *DeterministicClock) WaitForNewPendingTaskWithTimeout(timeout time.Duration) bool {
ctx, cancel := context.WithTimeout(context.Background(), timeout)
defer cancel()
return s.WaitForNewPendingTask(ctx)
}
// WaitForNewPendingTask blocks until a new task is scheduled since the last time this method was called.
// true is returned if a new task was scheduled, false if the context completed before a new task was added.
func (s *DeterministicClock) WaitForNewPendingTask(ctx context.Context) bool {
select {
case <-ctx.Done():
return false
case <-s.newPendingCh:
return true
}
}
// AdvanceTime moves the time forward by the specific duration
func (s *DeterministicClock) AdvanceTime(d time.Duration) {
s.lock.Lock()
defer s.lock.Unlock()
s.now = s.now.Add(d)
var remaining []action
for _, a := range s.pending {
if !a.isDue(s.now) || a.fire(s.now) {
remaining = append(remaining, a)
}
}
s.pending = remaining
}
var _ Clock = (*DeterministicClock)(nil)