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package raft
import (
"sync"
"sync/atomic"
)
// RaftState captures the state of a Raft node: Follower, Candidate, Leader,
// or Shutdown.
type RaftState uint32
const (
// Follower is the initial state of a Raft node.
Follower RaftState = iota
// Candidate is one of the valid states of a Raft node.
Candidate
// Leader is one of the valid states of a Raft node.
Leader
// Shutdown is the terminal state of a Raft node.
Shutdown
)
func (s RaftState) String() string {
switch s {
case Follower:
return "Follower"
case Candidate:
return "Candidate"
case Leader:
return "Leader"
case Shutdown:
return "Shutdown"
default:
return "Unknown"
}
}
// raftState is used to maintain various state variables
// and provides an interface to set/get the variables in a
// thread safe manner.
type raftState struct {
// currentTerm commitIndex, lastApplied, must be kept at the top of
// the struct so they're 64 bit aligned which is a requirement for
// atomic ops on 32 bit platforms.
// The current term, cache of StableStore
currentTerm uint64
// Highest committed log entry
commitIndex uint64
// Last applied log to the FSM
lastApplied uint64
// protects 4 next fields
lastLock sync.Mutex
// Cache the latest snapshot index/term
lastSnapshotIndex uint64
lastSnapshotTerm uint64
// Cache the latest log from LogStore
lastLogIndex uint64
lastLogTerm uint64
// Tracks running goroutines
routinesGroup sync.WaitGroup
// The current state
state RaftState
}
func (r *raftState) getState() RaftState {
stateAddr := (*uint32)(&r.state)
return RaftState(atomic.LoadUint32(stateAddr))
}
func (r *raftState) setState(s RaftState) {
stateAddr := (*uint32)(&r.state)
atomic.StoreUint32(stateAddr, uint32(s))
}
func (r *raftState) getCurrentTerm() uint64 {
return atomic.LoadUint64(&r.currentTerm)
}
func (r *raftState) setCurrentTerm(term uint64) {
atomic.StoreUint64(&r.currentTerm, term)
}
func (r *raftState) getLastLog() (index, term uint64) {
r.lastLock.Lock()
index = r.lastLogIndex
term = r.lastLogTerm
r.lastLock.Unlock()
return
}
func (r *raftState) setLastLog(index, term uint64) {
r.lastLock.Lock()
r.lastLogIndex = index
r.lastLogTerm = term
r.lastLock.Unlock()
}
func (r *raftState) getLastSnapshot() (index, term uint64) {
r.lastLock.Lock()
index = r.lastSnapshotIndex
term = r.lastSnapshotTerm
r.lastLock.Unlock()
return
}
func (r *raftState) setLastSnapshot(index, term uint64) {
r.lastLock.Lock()
r.lastSnapshotIndex = index
r.lastSnapshotTerm = term
r.lastLock.Unlock()
}
func (r *raftState) getCommitIndex() uint64 {
return atomic.LoadUint64(&r.commitIndex)
}
func (r *raftState) setCommitIndex(index uint64) {
atomic.StoreUint64(&r.commitIndex, index)
}
func (r *raftState) getLastApplied() uint64 {
return atomic.LoadUint64(&r.lastApplied)
}
func (r *raftState) setLastApplied(index uint64) {
atomic.StoreUint64(&r.lastApplied, index)
}
// Start a goroutine and properly handle the race between a routine
// starting and incrementing, and exiting and decrementing.
func (r *raftState) goFunc(f func()) {
r.routinesGroup.Add(1)
go func() {
defer r.routinesGroup.Done()
f()
}()
}
func (r *raftState) waitShutdown() {
r.routinesGroup.Wait()
}
// getLastIndex returns the last index in stable storage.
// Either from the last log or from the last snapshot.
func (r *raftState) getLastIndex() uint64 {
r.lastLock.Lock()
defer r.lastLock.Unlock()
return max(r.lastLogIndex, r.lastSnapshotIndex)
}
// getLastEntry returns the last index and term in stable storage.
// Either from the last log or from the last snapshot.
func (r *raftState) getLastEntry() (uint64, uint64) {
r.lastLock.Lock()
defer r.lastLock.Unlock()
if r.lastLogIndex >= r.lastSnapshotIndex {
return r.lastLogIndex, r.lastLogTerm
}
return r.lastSnapshotIndex, r.lastSnapshotTerm
}
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