time: add (*Timer).Reset(d Duration)

[Sajmani]

Some use cases for timers require extending the timer's deadline or resetting it to fire
again.  Implementing this using the existing time functions NewTimer and AfterFunc is
somewhat awkward and error-prone.  Instead, let's add:
  // Reset resets the time remaining on the timer to d.
  func (*Timer) Reset(d Duration)

[gopherbot]

Comment 1 by eric.d.eisner:

Is it implied that this function would also clear the channel's queue? Otherwise a Reset
followed by a channel read could fire immediately, which sounds like surprising behavior.

[gopherbot]

Comment 2 by eric.d.eisner:

Or maybe to encourage reusing Timers in recurring timeouts, the signature could be:
func (t *Timer) Reset(d Duration) <-chan Time
Which would just return the same channel every time.

[Sajmani]

Comment 3:

I don't think we should make any guarantees about the channel contents, since this is
racy.  But perhaps Reset should expose the same information as Stop, that is, a boolean
indicating whether the Reset happened before the timer fired.  But I would omit even
that bit for now, until there's a demonstrated need.

[gopherbot]

Comment 4 by eric.d.eisner:

Ensuring the channel is cleared could be made unracy, but the non-blocking channel read
would have to move into runtime under the global timer lock.

[rsc]

Comment 5:

It is probably worth returning the bool.
I strongly prefer not to muck with channel internals to undo a send.

[rsc]

Comment 6:

Labels changed: added size-l.

[rsc]

Comment 7:

Labels changed: added priority-later, removed priority-triage.

[adg]

Comment 8:

This issue was closed by revision 44ff17e.

Status changed to Fixed.