ZAB状态机
QuorumPeer这个线程负责状态机的维护
@Override
public void run() {
...
try {
/*
* Main loop
*/
while (running) {
switch (getPeerState()) {
//初始状态
case LOOKING:
LOG.info("LOOKING");
//允许只读服务
if (Boolean.getBoolean("readonlymode.enabled")) {
} else {
try {
setBCVote(null);
//发起leader选举
setCurrentVote(makeLEStrategy().lookForLeader());
} catch (Exception e) {
LOG.warn("Unexpected exception", e);
setPeerState(ServerState.LOOKING);
}
}
break;
case OBSERVING:
try {
LOG.info("OBSERVING");
setObserver(makeObserver(logFactory));
observer.observeLeader();
} catch (Exception e) {
LOG.warn("Unexpected exception",e );
} finally {
observer.shutdown();
setObserver(null);
setPeerState(ServerState.LOOKING);
}
break;
case FOLLOWING:
try {
LOG.info("FOLLOWING");
setFollower(makeFollower(logFactory));
//陷入发现，同步和广播阶段
follower.followLeader();
} catch (Exception e) {
LOG.warn("Unexpected exception",e);
} finally {
follower.shutdown();
setFollower(null);
setPeerState(ServerState.LOOKING);
}
break;
case LEADING:
LOG.info("LEADING");
try {
setLeader(makeLeader(logFactory));
//同步，广播
leader.lead();
setLeader(null);
} catch (Exception e) {
LOG.warn("Unexpected exception",e);
} finally {
if (leader != null) {
leader.shutdown("Forcing shutdown");
setLeader(null);
}
setPeerState(ServerState.LOOKING);
}
break;
}
}
}
}