bug: Timer callbacks may still be invoked even after the timer has been canceled

[jdx2013519]

 callingExpiredTimers_ = true;
 cancelingTimers_.clear();
  for (const Entry& it : expired)
  {
    it.second->run();
  }
  callingExpiredTimers_ = false;

if you cancel the timer in callback, the next timer will still run. so you should try to judge timer if it is in cancelingTimers_ beforn callback

 callingExpiredTimers_ = true;
 cancelingTimers_.clear();
  for (const Entry& it : expired)
  {
// if it is in cancelingtimers
    it.second->run();
  }
  callingExpiredTimers_ = false;

[chenshuo]

Yes, PRs are welcome.