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RaftMachine.java
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RaftMachine.java
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/*
* Copyright (c) 2002-2018 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.causalclustering.core.consensus;
import java.io.IOException;
import java.time.Clock;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;
import java.util.concurrent.TimeoutException;
import java.util.function.Predicate;
import org.neo4j.causalclustering.core.consensus.log.RaftLog;
import org.neo4j.causalclustering.core.consensus.log.cache.InFlightCache;
import org.neo4j.causalclustering.core.consensus.membership.RaftMembershipManager;
import org.neo4j.causalclustering.core.consensus.outcome.ConsensusOutcome;
import org.neo4j.causalclustering.core.consensus.outcome.Outcome;
import org.neo4j.causalclustering.core.consensus.roles.Role;
import org.neo4j.causalclustering.core.consensus.schedule.TimerService;
import org.neo4j.causalclustering.core.consensus.shipping.RaftLogShippingManager;
import org.neo4j.causalclustering.core.consensus.state.ExposedRaftState;
import org.neo4j.causalclustering.core.consensus.state.RaftState;
import org.neo4j.causalclustering.core.consensus.term.TermState;
import org.neo4j.causalclustering.core.consensus.vote.VoteState;
import org.neo4j.causalclustering.core.state.snapshot.RaftCoreState;
import org.neo4j.causalclustering.core.state.storage.StateStorage;
import org.neo4j.causalclustering.helper.VolatileFuture;
import org.neo4j.causalclustering.identity.MemberId;
import org.neo4j.causalclustering.messaging.Outbound;
import org.neo4j.kernel.monitoring.Monitors;
import org.neo4j.logging.Log;
import org.neo4j.logging.LogProvider;
import static java.lang.String.format;
import static org.neo4j.causalclustering.core.consensus.roles.Role.LEADER;
/**
* Implements the Raft Consensus Algorithm.
* <p>
* The algorithm is driven by incoming messages provided to {@link #handle}.
*/
public class RaftMachine implements LeaderLocator, CoreMetaData
{
private final LeaderNotFoundMonitor leaderNotFoundMonitor;
private InFlightCache inFlightCache;
public enum Timeouts implements TimerService.TimerName
{
ELECTION,
HEARTBEAT
}
private final RaftState state;
private final MemberId myself;
private final LeaderAvailabilityTimers leaderAvailabilityTimers;
private RaftMembershipManager membershipManager;
private final VolatileFuture<MemberId> volatileLeader = new VolatileFuture<>( null );
private final Outbound<MemberId,RaftMessages.RaftMessage> outbound;
private final Log log;
private Role currentRole = Role.FOLLOWER;
private RaftLogShippingManager logShipping;
public RaftMachine( MemberId myself, StateStorage<TermState> termStorage, StateStorage<VoteState> voteStorage, RaftLog entryLog,
LeaderAvailabilityTimers leaderAvailabilityTimers, Outbound<MemberId,RaftMessages.RaftMessage> outbound, LogProvider logProvider,
RaftMembershipManager membershipManager, RaftLogShippingManager logShipping, InFlightCache inFlightCache, boolean refuseToBecomeLeader,
boolean supportPreVoting, Monitors monitors )
{
this.myself = myself;
this.leaderAvailabilityTimers = leaderAvailabilityTimers;
this.outbound = outbound;
this.logShipping = logShipping;
this.log = logProvider.getLog( getClass() );
this.membershipManager = membershipManager;
this.inFlightCache = inFlightCache;
this.state = new RaftState( myself, termStorage, membershipManager, entryLog, voteStorage, inFlightCache,
logProvider, supportPreVoting, refuseToBecomeLeader );
leaderNotFoundMonitor = monitors.newMonitor( LeaderNotFoundMonitor.class );
}
/**
* This should be called after the major recovery operations are complete. Before this is called
* this instance cannot become a leader (the timers are disabled) and entries will not be cached
* in the in-flight map, because the application process is not running and ready to consume them.
*/
public synchronized void postRecoveryActions()
{
leaderAvailabilityTimers.start( this::electionTimeout,
clock -> handle( RaftMessages.ReceivedInstantAwareMessage.of( clock.instant(), new RaftMessages.Timeout.Heartbeat( myself ) ) ) );
inFlightCache.enable();
}
public synchronized void stopTimers()
{
leaderAvailabilityTimers.stop();
}
private synchronized void electionTimeout( Clock clock ) throws IOException
{
if ( leaderAvailabilityTimers.isElectionTimedOut() )
{
triggerElection( clock );
}
}
public void triggerElection( Clock clock ) throws IOException
{
handle( RaftMessages.ReceivedInstantAwareMessage.of( clock.instant(), new RaftMessages.Timeout.Election( myself ) ) );
}
public void panic()
{
stopTimers();
}
public synchronized RaftCoreState coreState()
{
return new RaftCoreState( membershipManager.getCommitted() );
}
public synchronized void installCoreState( RaftCoreState coreState ) throws IOException
{
membershipManager.install( coreState.committed() );
}
public synchronized void setTargetMembershipSet( Set<MemberId> targetMembers )
{
membershipManager.setTargetMembershipSet( targetMembers );
if ( currentRole == LEADER )
{
membershipManager.onFollowerStateChange( state.followerStates() );
}
}
@Override
public MemberId getLeader() throws NoLeaderFoundException
{
return waitForLeader( 0, Objects::nonNull );
}
private MemberId waitForLeader( long timeoutMillis, Predicate<MemberId> predicate ) throws NoLeaderFoundException
{
try
{
return volatileLeader.get( timeoutMillis, predicate );
}
catch ( InterruptedException e )
{
Thread.currentThread().interrupt();
leaderNotFoundMonitor.increment();
throw new NoLeaderFoundException( e );
}
catch ( TimeoutException e )
{
leaderNotFoundMonitor.increment();
throw new NoLeaderFoundException( e );
}
}
private Collection<LeaderListener> leaderListeners = new ArrayList<>();
@Override
public synchronized void registerListener( LeaderListener listener )
{
leaderListeners.add( listener );
listener.onLeaderSwitch( state.leaderInfo() );
}
@Override
public synchronized void unregisterListener( LeaderListener listener )
{
leaderListeners.remove( listener );
}
/**
* Every call to state() gives you an immutable copy of the current state.
*
* @return A fresh view of the state.
*/
public synchronized ExposedRaftState state()
{
return state.copy();
}
private void notifyLeaderChanges( Outcome outcome )
{
for ( LeaderListener listener : leaderListeners )
{
listener.onLeaderEvent( outcome );
}
}
private void handleLogShipping( Outcome outcome )
{
LeaderContext leaderContext = new LeaderContext( outcome.getTerm(), outcome.getLeaderCommit() );
if ( outcome.isElectedLeader() )
{
logShipping.resume( leaderContext );
}
else if ( outcome.isSteppingDown() )
{
logShipping.pause();
}
if ( outcome.getRole() == LEADER )
{
logShipping.handleCommands( outcome.getShipCommands(), leaderContext );
}
}
private boolean leaderChanged( Outcome outcome, MemberId oldLeader )
{
return !Objects.equals( oldLeader, outcome.getLeader() );
}
public synchronized ConsensusOutcome handle( RaftMessages.RaftMessage incomingMessage ) throws IOException
{
Outcome outcome = currentRole.handler.handle( incomingMessage, state, log );
boolean newLeaderWasElected = leaderChanged( outcome, state.leader() );
state.update( outcome ); // updates to raft log happen within
sendMessages( outcome );
handleTimers( outcome );
handleLogShipping( outcome );
driveMembership( outcome );
volatileLeader.set( outcome.getLeader() );
if ( newLeaderWasElected )
{
notifyLeaderChanges( outcome );
}
return outcome;
}
private void driveMembership( Outcome outcome ) throws IOException
{
membershipManager.processLog( outcome.getCommitIndex(), outcome.getLogCommands() );
currentRole = outcome.getRole();
membershipManager.onRole( currentRole );
if ( currentRole == LEADER )
{
membershipManager.onFollowerStateChange( state.followerStates() );
}
}
private void handleTimers( Outcome outcome )
{
if ( outcome.electionTimeoutRenewed() )
{
leaderAvailabilityTimers.renewElection();
}
}
private void sendMessages( Outcome outcome )
{
for ( RaftMessages.Directed outgoingMessage : outcome.getOutgoingMessages() )
{
try
{
outbound.send( outgoingMessage.to(), outgoingMessage.message() );
}
catch ( Exception e )
{
log.warn( format( "Failed to send message %s.", outgoingMessage ), e );
}
}
}
@Override
public boolean isLeader()
{
return currentRole == LEADER;
}
public Role currentRole()
{
return currentRole;
}
public MemberId identity()
{
return myself;
}
public RaftLogShippingManager logShippingManager()
{
return logShipping;
}
@Override
public String toString()
{
return format( "RaftInstance{role=%s, term=%d, currentMembers=%s}", currentRole, term(), votingMembers() );
}
public static class BootstrapException extends Exception
{
BootstrapException( Throwable cause )
{
super( cause );
}
}
public long term()
{
return state.term();
}
public Set<MemberId> votingMembers()
{
return membershipManager.votingMembers();
}
public Set<MemberId> replicationMembers()
{
return membershipManager.replicationMembers();
}
}