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RaftInstance.java
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RaftInstance.java
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/*
* Copyright (c) 2002-2016 "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.coreedge.raft;
import org.neo4j.coreedge.helper.VolatileFuture;
import org.neo4j.coreedge.raft.log.RaftLog;
import org.neo4j.coreedge.raft.log.RaftLogCompactedException;
import org.neo4j.coreedge.raft.log.RaftLogEntry;
import org.neo4j.coreedge.raft.membership.RaftGroup;
import org.neo4j.coreedge.raft.membership.RaftMembershipManager;
import org.neo4j.coreedge.raft.net.Inbound;
import org.neo4j.coreedge.raft.net.Outbound;
import org.neo4j.coreedge.raft.outcome.AppendLogEntry;
import org.neo4j.coreedge.raft.outcome.Outcome;
import org.neo4j.coreedge.raft.replication.shipping.RaftLogShippingManager;
import org.neo4j.coreedge.raft.roles.Role;
import org.neo4j.coreedge.raft.state.RaftState;
import org.neo4j.coreedge.raft.state.ReadableRaftState;
import org.neo4j.coreedge.raft.state.StateStorage;
import org.neo4j.coreedge.raft.state.term.TermState;
import org.neo4j.coreedge.raft.state.vote.VoteState;
import org.neo4j.kernel.impl.util.Listener;
import org.neo4j.kernel.internal.DatabaseHealth;
import org.neo4j.kernel.monitoring.Monitors;
import org.neo4j.logging.Log;
import org.neo4j.logging.LogProvider;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Set;
import java.util.concurrent.TimeoutException;
import java.util.function.Predicate;
import java.util.function.Supplier;
import static java.lang.String.format;
import static java.util.Collections.singletonList;
import static org.neo4j.coreedge.raft.roles.Role.LEADER;
/**
* The core raft class representing a member of the raft group. The main interactions are
* with the network and the entry log.
* <p/>
* The network is represented by the inbound and outbound classes, and inbound messages are
* handled by the core state machine, which in turn can generate outbound messages in
* response.
* <p/>
* The raft entry log persists the user data which the raft system safely replicates. The raft
* algorithm ensures that these logs eventually are fed with the exact same entries, even in
* the face of failures.
* <p/>
* The main entry point for adding a new entry is the sendToLeader() function, which starts of
* the process of safe replication. The new entry will be safely replicated and eventually
* added to the local log through a call to the append() function of the entry log. Eventually
* the leader will have replicated it safely, and at a later point in time the commit() function
* of the entry log will be called.
*
* @param <MEMBER> The membership type.
*/
public class RaftInstance<MEMBER> implements LeaderLocator<MEMBER>,
Inbound.MessageHandler<RaftMessages.RaftMessage<MEMBER>>, CoreMetaData
{
private final LeaderNotFoundMonitor leaderNotFoundMonitor;
public enum Timeouts implements RenewableTimeoutService.TimeoutName
{
ELECTION, HEARTBEAT
}
private final RaftState<MEMBER> state;
private final MEMBER myself;
private final RaftLog entryLog;
private final RenewableTimeoutService renewableTimeoutService;
private final long heartbeatInterval;
private RenewableTimeoutService.RenewableTimeout electionTimer;
private RaftMembershipManager<MEMBER> membershipManager;
private final RaftStateMachine raftStateMachine;
private final long electionTimeout;
private final Supplier<DatabaseHealth> databaseHealthSupplier;
private final VolatileFuture<MEMBER> volatileLeader = new VolatileFuture<>( null );
private final Outbound<MEMBER> outbound;
private final Log log;
private Role currentRole = Role.FOLLOWER;
private RaftLogShippingManager<MEMBER> logShipping;
public RaftInstance( MEMBER myself, StateStorage<TermState> termStorage,
StateStorage<VoteState<MEMBER>> voteStorage, RaftLog entryLog,
RaftStateMachine raftStateMachine, long electionTimeout, long heartbeatInterval,
RenewableTimeoutService renewableTimeoutService,
final Inbound<RaftMessages.RaftMessage<MEMBER>> inbound, final Outbound<MEMBER> outbound,
LogProvider logProvider, RaftMembershipManager<MEMBER> membershipManager,
RaftLogShippingManager<MEMBER> logShipping,
Supplier<DatabaseHealth> databaseHealthSupplier,
Monitors monitors )
{
this.myself = myself;
this.entryLog = entryLog;
this.raftStateMachine = raftStateMachine;
this.electionTimeout = electionTimeout;
this.heartbeatInterval = heartbeatInterval;
this.renewableTimeoutService = renewableTimeoutService;
this.outbound = outbound;
this.logShipping = logShipping;
this.databaseHealthSupplier = databaseHealthSupplier;
this.log = logProvider.getLog( getClass() );
this.membershipManager = membershipManager;
this.state = new RaftState<>( myself, termStorage, membershipManager, entryLog, voteStorage );
leaderNotFoundMonitor = monitors.newMonitor( LeaderNotFoundMonitor.class );
initTimers();
inbound.registerHandler( this );
}
private void initTimers()
{
electionTimer = renewableTimeoutService.create(
Timeouts.ELECTION, electionTimeout, randomTimeoutRange(), timeout -> {
handle( new RaftMessages.Timeout.Election<>( myself ) );
timeout.renew();
} );
renewableTimeoutService.create(
Timeouts.HEARTBEAT, heartbeatInterval, 0, timeout -> {
handle( new RaftMessages.Timeout.Heartbeat<>( myself ) );
timeout.renew();
} );
}
/**
* All members must be bootstrapped with the exact same set of initial members. Bootstrapping
* requires an empty log as input and will seed it with the initial group entry in term 0.
*
* @param memberSet The other members.
*/
public synchronized void bootstrapWithInitialMembers( RaftGroup<MEMBER> memberSet ) throws BootstrapException, RaftLogCompactedException
{
if ( entryLog.appendIndex() >= 0 )
{
return;
}
RaftLogEntry membershipLogEntry = new RaftLogEntry( 0, memberSet );
try
{
Outcome<MEMBER> outcome = new Outcome<>( currentRole, state );
outcome.setCommitIndex( 0 );
AppendLogEntry appendCommand = new AppendLogEntry( 0, membershipLogEntry );
outcome.addLogCommand( appendCommand );
state.update( outcome );
membershipManager.processLog( 0, singletonList( appendCommand ) );
}
catch ( IOException e )
{
databaseHealthSupplier.get().panic( e );
throw new BootstrapException( e );
}
}
public void setTargetMembershipSet( Set<MEMBER> targetMembers )
{
membershipManager.setTargetMembershipSet( targetMembers );
if ( currentRole == LEADER )
{
membershipManager.onFollowerStateChange( state.followerStates() );
}
}
@Override
public MEMBER getLeader() throws NoLeaderFoundException
{
return waitForLeader( 0, member -> member != null );
}
public MEMBER waitForLeader( long timeoutMillis, Predicate<MEMBER> 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<Listener<MEMBER>> leaderListeners = new ArrayList<>();
@Override
public synchronized void registerListener( Listener<MEMBER> listener )
{
leaderListeners.add( listener );
listener.receive( state.leader() );
}
@Override
public synchronized void unregisterListener( Listener<MEMBER> listener )
{
leaderListeners.remove( listener );
}
public ReadableRaftState<MEMBER> state()
{
return state;
}
private void checkForSnapshotNeed( Outcome<MEMBER> outcome )
{
if( outcome.needsFreshSnapshot() )
{
raftStateMachine.notifyNeedFreshSnapshot();
}
}
private void notifyLeaderChanges( Outcome<MEMBER> outcome )
{
for ( Listener<MEMBER> listener : leaderListeners )
{
listener.receive( outcome.getLeader() );
}
}
private void handleLogShipping( Outcome<MEMBER> outcome ) throws IOException
{
LeaderContext leaderContext = new LeaderContext( outcome.getTerm(), outcome.getLeaderCommit() );
if ( outcome.isElectedLeader() )
{
logShipping.start( leaderContext );
}
else if ( outcome.isSteppingDown() )
{
logShipping.stop();
}
if( outcome.getRole() == LEADER )
{
logShipping.handleCommands( outcome.getShipCommands(), leaderContext );
}
}
private boolean leaderChanged( Outcome<MEMBER> outcome, MEMBER oldLeader )
{
if ( oldLeader == null && outcome.getLeader() != null )
{
return true;
}
else if ( oldLeader != null && !oldLeader.equals( outcome.getLeader() ) )
{
return true;
}
return false;
}
public synchronized void handle( RaftMessages.RaftMessage<MEMBER> incomingMessage )
{
try
{
Outcome<MEMBER> outcome = currentRole.handler.handle( incomingMessage, state, log );
boolean newLeaderWasElected = leaderChanged( outcome, state.leader() );
boolean newCommittedEntry = outcome.getCommitIndex() > state.commitIndex();
state.update( outcome ); // updates to raft log happen within
sendMessages( outcome );
handleTimers( outcome );
handleLogShipping( outcome );
membershipManager.processLog( outcome.getCommitIndex(), outcome.getLogCommands() );
driveMembership( outcome );
volatileLeader.set( outcome.getLeader() );
if( newCommittedEntry )
{
raftStateMachine.notifyCommitted( state.commitIndex() );
}
if( newLeaderWasElected )
{
notifyLeaderChanges( outcome );
}
checkForSnapshotNeed( outcome );
}
catch ( Throwable e )
{
// TODO: perhaps try to recover from some errors, like IllegalArgumentExceptions from the log
log.error( "Failed to process RAFT message " + incomingMessage, e );
databaseHealthSupplier.get().panic( e );
}
}
private void driveMembership( Outcome<MEMBER> outcome )
{
currentRole = outcome.getRole();
membershipManager.onRole( currentRole );
if ( currentRole == LEADER )
{
membershipManager.onFollowerStateChange( state.followerStates() );
}
}
private void handleTimers( Outcome<MEMBER> outcome )
{
if ( outcome.electionTimeoutRenewed() )
{
electionTimer.renew();
}
}
private void sendMessages( Outcome<MEMBER> outcome )
{
for ( RaftMessages.Directed<MEMBER> outgoingMessage : outcome.getOutgoingMessages() )
{
outbound.send( outgoingMessage.to(), outgoingMessage.message() );
}
}
@Override
public boolean isLeader()
{
return currentRole == LEADER;
}
public Role currentRole()
{
return currentRole;
}
public MEMBER 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
{
public BootstrapException( Throwable cause )
{
super( cause );
}
}
public long term()
{
return state.term();
}
private long randomTimeoutRange()
{
return electionTimeout;
}
public Set<MEMBER> votingMembers()
{
return membershipManager.votingMembers();
}
public Set<MEMBER> replicationMembers()
{
return membershipManager.replicationMembers();
}
}