com.bigdata.quorum

Class AbstractQuorum.QuorumWatcherBase

java.lang.Object

com.bigdata.quorum.AbstractQuorum.QuorumWatcherBase

All Implemented Interfaces:

QuorumWatcher<S,C>

Direct Known Subclasses:

MockQuorumFixture.MockQuorum.MockQuorumWatcher

Enclosing class:

AbstractQuorum<S extends Remote,C extends QuorumClient<S>>

protected abstract class AbstractQuorum.QuorumWatcherBase
extends Object
implements QuorumWatcher<S,C>

Base class for QuorumWatcher implementations.

The protected methods on this base class are designed to be invoked by the QuorumWatcher when it observes a change in the distributed quorum state. Those methods know how to update the internal state of the AbstractQuorum based on state changes observed by a concrete QuorumWatcher implementations and will generate the appropriate messages for the QuorumClient or QuorumMember and also generate the appropriate QuorumEvents.

When a state change triggers certain events on the behalf of the associated QuorumMember the QuorumWatcher will issue the necessary requests to the QuorumActor. For example, when the #of joined services rises to (k+1)/2, the QuorumWatcher for the first service in the vote order will issue the requests to the QuorumActor which are necessary to execute the leader election protocol.

Field Summary

Fields

Modifier and Type	Field and Description
protected String	logicalServiceId The identifier of the logical service whose quorum state is being watched.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	AbstractQuorum.QuorumWatcherBase(String logicalServiceId)

Method Summary

Methods

Modifier and Type	Method and Description
protected void	castVote(UUID serviceId, long lastCommitTime) Method is invoked by the QuorumWatcher when a service is votes in an attempt to join a quorum and updates the internal state of the quorum to reflect that state change.
protected void	clearToken() Method is invoked by the QuorumWatcher when the current quorum token is invalidated.
protected void	doAction(Runnable r) Run some action(s) on the behalf of the watcher outside of the thread in which the watcher handles the state change (this is done to avoid recursion through the watcher-action loop while holding the lock).
protected void	memberAdd(UUID serviceId) Method is invoked by the QuorumWatcher when a member service is added to the quorum and updates the internal state of the quorum to reflect that state change.
protected void	memberRemove(UUID serviceId) Method is invoked by the QuorumWatcher when a member service is removed from the quorum and updates the internal state of the quorum to reflect that state change.
protected void	pipelineAdd(UUID serviceId) Method is invoked by the QuorumWatcher when a service is added to the write pipeline and updates the internal state of the quorum to reflect that state change.
protected void	pipelineRemove(UUID serviceId) Method is invoked by the QuorumWatcher when a service is removed from the write pipeline and updates the internal state of the quorum to reflect that state change.
protected void	serviceJoin(UUID serviceId) Method is invoked by the QuorumWatcher when a service joins the quorum and updates the internal state of the quorum to reflect that state change.
protected void	serviceLeave(UUID serviceId) Method is invoked by the QuorumWatcher when a joined service leaves the quorum and updates the internal state of the quorum to reflect that state change.
protected void	setToken(long newToken) Method is invoked by the QuorumWatcher when the leader updates the (lastValidToken,token) pair atomically.
protected void	start() Method is invoked by AbstractQuorum.start(QuorumClient) and provides the QuorumWatcher with an opportunity to setup discovery (such as zookeeper watchers) and read the initial state of the distributed quorum, causing it to be reflected on the AbstractQuorum internal state.
protected void	terminate() Method is invoked by AbstractQuorum.terminate() and provides the QuorumWatcher with an opportunity to terminate asynchronous processing and tear down any resources it may be using.
protected void	withdrawVote(UUID serviceId) Method is invoked by the QuorumWatcher when a service has withdrawn its vote for some lastCommitTime.

Methods inherited from class java.lang.Object

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

Field Detail

logicalServiceId

protected final String logicalServiceId

The identifier of the logical service whose quorum state is being watched.

Constructor Detail

AbstractQuorum.QuorumWatcherBase

protected AbstractQuorum.QuorumWatcherBase(String logicalServiceId)

Method Detail

start

protected void start()

Method is invoked by AbstractQuorum.start(QuorumClient) and provides the QuorumWatcher with an opportunity to setup discovery (such as zookeeper watchers) and read the initial state of the distributed quorum, causing it to be reflected on the AbstractQuorum internal state.

terminate

protected void terminate()

Method is invoked by AbstractQuorum.terminate() and provides the QuorumWatcher with an opportunity to terminate asynchronous processing and tear down any resources it may be using.

doAction

protected void doAction(Runnable r)

Run some action(s) on the behalf of the watcher outside of the thread in which the watcher handles the state change (this is done to avoid recursion through the watcher-action loop while holding the lock).

Parameters:

r - The action(s).

memberAdd

protected void memberAdd(UUID serviceId)

Method is invoked by the QuorumWatcher when a member service is added to the quorum and updates the internal state of the quorum to reflect that state change.

Parameters:

serviceId - The service UUID.

memberRemove

protected void memberRemove(UUID serviceId)

Method is invoked by the QuorumWatcher when a member service is removed from the quorum and updates the internal state of the quorum to reflect that state change.

Parameters:

serviceId - The service UUID.

pipelineAdd

protected void pipelineAdd(UUID serviceId)

Method is invoked by the QuorumWatcher when a service is added to the write pipeline and updates the internal state of the quorum to reflect that state change.

Parameters:

serviceId - The service UUID.

pipelineRemove

protected void pipelineRemove(UUID serviceId)

Method is invoked by the QuorumWatcher when a service is removed from the write pipeline and updates the internal state of the quorum to reflect that state change.

Parameters:

serviceId - The service UUID.

castVote

protected void castVote(UUID serviceId,
            long lastCommitTime)

Method is invoked by the QuorumWatcher when a service is votes in an attempt to join a quorum and updates the internal state of the quorum to reflect that state change. Each service has a single vote to cast. If the service casts a different vote, then its old vote must first be withdrawn. Once (k+1)/2 services vote for the same lastCommitTime, the client will be notified with a quorumMeet() event. Once a quorum meets on a lastCommitTime, cast votes should be left in place (or withdrawn?). A new vote will be required if the quorum breaks. Services seeking to join a met quorum must first synchronize with the quorum.

Parameters:

serviceId - The service UUID.

lastCommitTime - The lastCommitTime timestamp for which that service casts its vote.

Throws:

IllegalArgumentException - if the serviceId is null.

IllegalArgumentException - if the lastCommitTime is negative.

withdrawVote

protected void withdrawVote(UUID serviceId)

Method is invoked by the QuorumWatcher when a service has withdrawn its vote for some lastCommitTime.

Note: If no votes remain for a given lastCommitTime, then the lastCommitTime is withdrawn from the internal pool of lastCommiTimes being considered. This ensures that we do not leak memory in that pool.

Parameters:

serviceId - The service UUID.

setToken

protected void setToken(long newToken)

Method is invoked by the QuorumWatcher when the leader updates the (lastValidToken,token) pair atomically.

Parameters:

newToken - The new token.

clearToken

protected void clearToken()

Method is invoked by the QuorumWatcher when the current quorum token is invalidated.

serviceJoin

protected void serviceJoin(UUID serviceId)

Method is invoked by the QuorumWatcher when a service joins the quorum and updates the internal state of the quorum to reflect that state change.

Parameters:

serviceId - The service UUID.

serviceLeave

protected void serviceLeave(UUID serviceId)

Method is invoked by the QuorumWatcher when a joined service leaves the quorum and updates the internal state of the quorum to reflect that state change.

Parameters:

serviceId - The service UUID.