raft/raft.go
func (r *raft) tickHeartbeat() {
	r.heartbeatElapsed++
	r.electionElapsed++

	if r.electionElapsed >= r.electionTimeout {
		r.electionElapsed = 0
		if r.checkQuorum {
			r.Step(pb.Message{From: r.id, Type: pb.MsgCheckQuorum})
		}
		// If current leader cannot transfer leadership in electionTimeout, it becomes leader again.
		if r.state == StateLeader && r.leadTransferee != None {
			r.abortLeaderTransfer()
		}
	}

	if r.state != StateLeader {
		return
	}

	if r.heartbeatElapsed >= r.heartbeatTimeout {
		r.heartbeatElapsed = 0
		r.Step(pb.Message{From: r.id, Type: pb.MsgBeat})
	}
}
func (r *raft) tickHeartbeat() {
	r.heartbeatElapsed++
	r.electionElapsed++

	if r.electionElapsed >= r.electionTimeout {
		r.electionElapsed = 0
		if r.checkQuorum {
			r.Step(pb.Message{From: r.id, Type: pb.MsgCheckQuorum})
		}
		// If current leader cannot transfer leadership in electionTimeout, it becomes leader again.
		if r.state == StateLeader && r.leadTransferee != None {
			r.abortLeaderTransfer()
		}
	}

	if r.state != StateLeader {
		return
	}

	if r.heartbeatElapsed >= r.heartbeatTimeout {
		r.heartbeatElapsed = 0
		r.Step(pb.Message{From: r.id, Type: pb.MsgBeat})
	}
}
// tickHeartbeat is run by leaders to send a MsgBeat after r.heartbeatTimeout.