聊聊artemis的QuorumVote
QuorumVote
activemq-artemis-2.11.0/artemis-server/src/main/java/org/apache/activemq/artemis/core/server/cluster/qourum/QuorumVote.java
public abstract class QuorumVote<V extends Vote, T> { private SimpleString name;
public QuorumVote(SimpleString name) {
this.name = name;
}
/**
* called by the {@link org.apache.activemq.artemis.core.server.cluster.qourum.QuorumManager} when one of the nodes in the quorum is
* successfully connected to. The QuorumVote can then decide whether or not a decision can be made with just that information.
*
* @return the vote to use
*/
public abstract Vote connected();
/**
* called by the {@link org.apache.activemq.artemis.core.server.cluster.qourum.QuorumManager} fails to connect to a node in the quorum.
* The QuorumVote can then decide whether or not a decision can be made with just that information however the node
* cannot cannot be asked.
*
* @return the vote to use
*/
public abstract Vote notConnected();
/**
* called by the {@link org.apache.activemq.artemis.core.server.cluster.qourum.QuorumManager} when a vote can be made, either from the
* cluster or decided by itself.
*
* @param vote the vote to make.
*/
public abstract void vote(V vote);
/**
* get the decion of the vote
*
* @return the voting decision
*/
public abstract T getDecision();
/**
* called by the {@link org.apache.activemq.artemis.core.server.cluster.qourum.QuorumManager} when all the votes have been cast and received.
*
* @param voteTopology the topology of where the votes were sent.
*/
public abstract void allVotesCast(Topology voteTopology);
/**
* the name of this quorum vote, used for identifying the correct {@link org.apache.activemq.artemis.core.server.cluster.qourum.QuorumVoteHandler}
*
* @return the name of the wuorum vote
*/
public SimpleString getName() {
return name;
}
}
- QuorumVote是个抽象类，定义了connected、notConnected、vote、getDecision、allVotesCast抽象方法
QuorumVoteServerConnect
activemq-artemis-2.11.0/artemis-server/src/main/java/org/apache/activemq/artemis/core/server/cluster/qourum/QuorumVoteServerConnect.java
public class QuorumVoteServerConnect extends QuorumVote<ServerConnectVote, Boolean> { public static final SimpleString LIVE_FAILOVER_VOTE = new SimpleString("LiveFailoverQuorumVote");
private final CountDownLatch latch;
private final String targetNodeId;
private final String liveConnector;
private int votesNeeded;
private int total = 0;
private boolean decision = false;
// Is this the live requesting to stay live, or a backup requesting to become live.
private boolean requestToStayLive = false;
/**
* live nodes | remaining nodes | majority | votes needed
* 1 | 0 | 0 | 0
* 2 | 1 | 1 | 1
* n | r = n-1 | n/2 + 1 | n/2 + 1 rounded
* 3 | 2 | 2.5 | 2
* 4 | 3 | 3 | 3
* 5 | 4 | 3.5 | 3
* 6 | 5 | 4 | 4
*/
public QuorumVoteServerConnect(int size, String targetNodeId, boolean requestToStayLive, String liveConnector) {
super(LIVE_FAILOVER_VOTE);
this.targetNodeId = targetNodeId;
this.liveConnector = liveConnector;
double majority;
if (size <= 2) {
majority = ((double) size) / 2;
} else {
//even
majority = ((double) size) / 2 + 1;
}
//votes needed could be say 2.5 so we add 1 in this case
votesNeeded = (int) majority;
latch = new CountDownLatch(votesNeeded);
if (votesNeeded == 0) {
decision = true;
}
this.requestToStayLive = requestToStayLive;
}
public QuorumVoteServerConnect(int size, String targetNodeId) {
this(size, targetNodeId, false, null);
}
/**
* if we can connect to a node
*
* @return
*/
@Override
public Vote connected() {
return new ServerConnectVote(targetNodeId, requestToStayLive, null);
}
/**
* if we cant connect to the node
*
* @return
*/
@Override
public Vote notConnected() {
return new BooleanVote(false);
}
/**
* live nodes | remaining nodes | majority | votes needed
* 1 | 0 | 0 | 0
* 2 | 1 | 1 | 1
* n | r = n-1 | n/2 + 1 | n/2 + 1 rounded
* 3 | 2 | 2.5 | 2
* 4 | 3 | 3 | 3
* 5 | 4 | 3.5 | 3
* 6 | 5 | 4 | 4
*
* @param vote the vote to make.
*/
@Override
public synchronized void vote(ServerConnectVote vote) {
if (decision)
return;
if (!requestToStayLive && vote.getVote()) {
total++;
latch.countDown();
if (total >= votesNeeded) {
decision = true;
}//do the opposite, if it says there is a node connected it means the backup has come live
} else if (requestToStayLive && vote.getVote()) {
total++;
latch.countDown();
if (liveConnector != null && !liveConnector.equals(vote.getTransportConfiguration())) {
ActiveMQServerLogger.LOGGER.qourumBackupIsLive(liveConnector);
return;
}
if (total >= votesNeeded) {
decision = true;
}
}
}
@Override
public void allVotesCast(Topology voteTopology) {
while (latch.getCount() > 0) {
latch.countDown();
}
}
@Override
public Boolean getDecision() {
return decision;
}
public void await(int latchTimeout, TimeUnit unit) throws InterruptedException {
ActiveMQServerLogger.LOGGER.waitingForQuorumVoteResults(latchTimeout, unit.toString().toLowerCase());
if (latch.await(latchTimeout, unit))
ActiveMQServerLogger.LOGGER.receivedAllQuorumVotes();
else
ActiveMQServerLogger.LOGGER.timeoutWaitingForQuorumVoteResponses();
}
public boolean isRequestToStayLive() {
return requestToStayLive;
}
}
- QuorumVoteServerConnect继承了QuorumVote，其构造器根据size初始化votesNeeded及decision；其connected方法返回ServerConnectVote；其notConnected方法返回BooleanVote(false)；其vote方法对于ServerConnectVote的vote为true的递增total，同时latch.countDown()，对于total大于等于votesNeeded的更新decision为true；其allVotesCast方法则循环latch.countDown()
小结
QuorumVote是个抽象类，定义了connected、notConnected、vote、getDecision、allVotesCast抽象方法；QuorumVoteServerConnect继承了QuorumVote，其构造器根据size初始化votesNeeded及decision；其connected方法返回ServerConnectVote；其notConnected方法返回BooleanVote(false)；其vote方法对于ServerConnectVote的vote为true的递增total，同时latch.countDown()，对于total大于等于votesNeeded的更新decision为true；其allVotesCast方法则循环latch.countDown()
doc
- QuorumVoteServerConnect
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