Simplify timer cleanup

The timer channels are created with a buffer. Because we aren't reusing them,
we don't need to worry about draining that channel; the internal
goroutine will still be able to write to the buffer and exit gracefully,
at which point the GC will clean it all up.

We *do* still need to call `Stop()` to tell the timer to clean up
immediately, as otherwise it will run for its full duration which (in a
tight loop) can cause timer goroutines to pile up.

deadline/deadline.go

@@ -42,10 +42,7 @@ func (d *Deadline) Run(work func(<-chan struct{}) error) error {
  timer := time.NewTimer(d.timeout)
  select {
  case ret := <-result:
- if !timer.Stop() {
- <-timer.C
- }
-
+ timer.Stop()
  return ret
  case <-timer.C:
  close(stopper)

retrier/retrier.go

@@ -96,10 +96,7 @@ func (r *Retrier) sleep(ctx context.Context, timer *time.Timer) error {
  case <-timer.C:
  return nil
  case <-ctx.Done():
- if !timer.Stop() {
- <-timer.C
- }
-
+ timer.Stop()
  return ctx.Err()
  }
 }

semaphore/semaphore.go

@@ -32,10 +32,7 @@ func (s *Semaphore) Acquire() error {
  timer := time.NewTimer(s.timeout)
  select {
  case s.sem <- struct{}{}:
- if !timer.Stop() {
- <-timer.C
- }
-
+ timer.Stop()
  return nil
  case <-timer.C:
  return ErrNoTickets