infoservice.agreement.paxos
Class PaxosAcceptor

java.lang.Object
  infoservice.agreement.paxos.PaxosObject
      infoservice.agreement.paxos.PaxosCommunicator
          infoservice.agreement.paxos.PaxosProposer
              infoservice.agreement.paxos.PaxosAcceptor

All Implemented Interfaces:

TimeoutListener

Direct Known Subclasses:

PaxosAdapter

public abstract class PaxosAcceptor
extends PaxosProposer
implements TimeoutListener

Field Summary

protected java.util.Hashtable

m_paxosInstances A collection of all running PAXOS instances

Fields inherited from class infoservice.agreement.paxos.PaxosProposer

m_lastRandom

Fields inherited from class infoservice.agreement.paxos.PaxosCommunicator

m_targets

Constructor Summary

PaxosAcceptor()

Method Summary

private void	addCollectMessage(PaxosMessage a_msg) Adds a CollectMessage.
private void	addDecideMessage(PaxosMessage a_msg) Adds a DecideMessage.
private void	addFreezeMessage(PaxosMessage a_msg) Adds a FreezeMessage.
private void	addFreezeProofMessage(PaxosMessage a_msg) Adds a FreezeProofMessage.
void	addMessage(PaxosMessage a_msg) This gets called if a PaxosMessage arrives.
private void	addProposeMessage(PaxosMessage a_msg) Adds a ProposeMessage.
private void	addStrongMessage(PaxosMessage a_msg) Adds a StrongMessage.
private void	addWeakMessage(PaxosMessage a_msg) Adds a WeakMessage.
private void	cloneMessage(PaxosMessage a_original, PaxosMessage a_target) Copies the attributes of the source message to the target message
private void	decide(PaxosRound a_round, PaxosMessage a_msg, boolean a_sendDecide) Decide for the proposal contained in the given message and send a DecideMessage to all processes if a_sendDecide is true
private void	freeze(PaxosRound a_round) Freezes the given round either if a timeout oocured or if we got more than f FreezeMessages
PaxosInstance	getPaxosInstance(java.lang.String a_paxosInstanceId) Returns the PaxosInstance identified by the given id
private PaxosRound	getPaxosRound(PaxosMessage a_msg) Returns the PaxosRound to which the given message belongs
protected java.util.Vector	getRoundLeaders()
protected abstract void	notifyAgreement(java.util.Hashtable a_agreements) Callback for implementing classes.
private void	strongAccept(PaxosRound a_round, PaxosMessage a_msg) Strongly accept the proposal contained in the given message an send a StrongMessage to all processes
void	timeout(java.lang.Object m_round) Callback method for the PaxosTimeout of a PaxosRound.
private void	weakAccept(PaxosRound a_round, PaxosMessage a_msg) Weakly accept the proposal contained in the given message and send a WeakMessage to all processes

Methods inherited from class infoservice.agreement.paxos.PaxosProposer

propose, setRound

Methods inherited from class infoservice.agreement.paxos.PaxosCommunicator

getF, getIdentifier, getN, getQuorumDecideStrong, getQuorumDecideWeak, getQuorumStrong, getQuorumTwoThird, getTargets, multicast, sendMessage, sendMessage, setTargets

Methods inherited from class infoservice.agreement.paxos.PaxosObject

debug, error, fatal, getLog, info, setLog

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

m_paxosInstances

protected java.util.Hashtable m_paxosInstances

A collection of all running PAXOS instances

Constructor Detail

PaxosAcceptor

public PaxosAcceptor()

Method Detail

addMessage

public void addMessage(PaxosMessage a_msg)

This gets called if a PaxosMessage arrives. The handling methods sort the message to the matching instance, execution and round

Parameters:

a_msg - The message to be handled

addCollectMessage

private void addCollectMessage(PaxosMessage a_msg)

Adds a CollectMessage. A CollectMessage contains a new proposal which has to be "good" according to the attached proof, otherwise it will not be accepted

Parameters:

a_msg - The CollectMessage to be handled

addFreezeProofMessage

private void addFreezeProofMessage(PaxosMessage a_msg)

Adds a FreezeProofMessage. A FreezeProofMessage contains the weakly accepted value and the strongly accepted value of the sender in the last round. These values as signed and will be used to compute a "good" proposal for the following round

Parameters:

a_msg - The FreezeProofMessage to be handled

addFreezeMessage

private void addFreezeMessage(PaxosMessage a_msg)

Adds a FreezeMessage. A FreezeMessage is sent by others if their local timeout for the matching round in the matching execution timed out. If we get more than f FreezeMessages we also freeze the round (because within the min f+1 FreezeMessages we received, at least one came frome an honest party)

Parameters:

a_msg - The FreezeMessage to add

addProposeMessage

private void addProposeMessage(PaxosMessage a_msg)

Adds a ProposeMessage. A ProposeMesssage is the first message of each execution. A value is proposed that should be accepted by all parties.

Parameters:

a_msg -

addWeakMessage

private void addWeakMessage(PaxosMessage a_msg)

Adds a WeakMessage. If a process weakly accepts a proposal, it sends a WeakMessage to all the others. It might be that a process doesn't get the matching proposal, so we add the posibility to weakly accept a value if at least f+1 have done so

Parameters:

a_msg - The WeakMessage to be added

addStrongMessage

private void addStrongMessage(PaxosMessage a_msg)

Adds a StrongMessage. A StrongMessage is sent by a process which strongly accepted the proposal.

Parameters:

a_msg - The StrongMessage to be added

addDecideMessage

private void addDecideMessage(PaxosMessage a_msg)

Adds a DecideMessage. DecideMessages are sent if a process decides for the porposal

Parameters:

a_msg - The DecideMessage to be added

weakAccept

private void weakAccept(PaxosRound a_round,
                        PaxosMessage a_msg)

Weakly accept the proposal contained in the given message and send a WeakMessage to all processes

Parameters:

a_round - The round the message belongs to

a_msg - The message which triggered the weak acceptance

cloneMessage

private void cloneMessage(PaxosMessage a_original,
                          PaxosMessage a_target)

Copies the attributes of the source message to the target message

Parameters:

a_original - The source message

a_target - The target message

strongAccept

private void strongAccept(PaxosRound a_round,
                          PaxosMessage a_msg)

Strongly accept the proposal contained in the given message an send a StrongMessage to all processes

Parameters:

a_round - The round the message belongs to

a_msg - The message which triggered the weak acceptance

decide

private void decide(PaxosRound a_round,
                    PaxosMessage a_msg,
                    boolean a_sendDecide)

Decide for the proposal contained in the given message and send a DecideMessage to all processes if a_sendDecide is true

Parameters:

a_round - The round the message belongs to

a_msg - The message which triggered the weak acceptance

a_sendDecide - If true a decide message is sent, otherwise not

freeze

private void freeze(PaxosRound a_round)

Freezes the given round either if a timeout oocured or if we got more than f FreezeMessages

Parameters:

a_round - The round to be frozen

timeout

public void timeout(java.lang.Object m_round)

Callback method for the PaxosTimeout of a PaxosRound. Freezes the round if it hasn't been decided yet

Specified by:

timeout in interface TimeoutListener

Parameters:

m_round -

getPaxosInstance

public PaxosInstance getPaxosInstance(java.lang.String a_paxosInstanceId)

Returns the PaxosInstance identified by the given id

Parameters:

a_paxosInstanceId - The ID of the instance to be returned

Returns:

The PaxosInstance with the given ID

getPaxosRound

private PaxosRound getPaxosRound(PaxosMessage a_msg)

Returns the PaxosRound to which the given message belongs

Parameters:

a_msg - The message used to determine the Round to be returned

Returns:

The PaxosRound to which the given message belongs

getRoundLeaders

protected java.util.Vector getRoundLeaders()

notifyAgreement

protected abstract void notifyAgreement(java.util.Hashtable a_agreements)

Callback for implementing classes. This gets called when agreement has been reached, that means every proposer proposed (which leads to an execution) and every execution has beed decided

Parameters:

a_agreements - Map of execution-identifier to decission