com.github.zk1931.jzab

Interface StateMachine

public interface StateMachine

The state machine interface for interacting with Zab.

Method Summary

Methods

Modifier and Type	Method and Description
void	deliver(Zxid zxid, ByteBuffer stateUpdate, String clientId, Object ctx) Callback for Zab.send(java.nio.ByteBuffer, java.lang.Object).
void	flushed(Zxid zxid, ByteBuffer flushRequest, Object ctx) Callback for Zab.flush(java.nio.ByteBuffer, java.lang.Object).
void	following(String leader, Set<String> clusterMembers) Notifies the state machine that Zab is in following phase with given leader and cluster members.
void	leading(Set<String> activeFollowers, Set<String> clusterMembers) Notifies the state machine that Zab is in leading phase with given sets of active followers and cluster members.
ByteBuffer	preprocess(Zxid zxid, ByteBuffer message) Converts a message to an idempotent transaction.
void	recovering(PendingRequests pendingRequests) Notifies the state machine that Zab is in recovering phase.
void	removed(String serverId, Object ctx) Callback for Zab.remove(java.lang.String, java.lang.Object).
void	restore(FileInputStream fis) Deserializes the application state from a FileInputStream.
void	save(FileOutputStream fos) Serializes the application state to a FileOutputStream.
void	snapshotDone(String filePath, Object ctx) Callback for Zab.takeSnapshot(java.lang.Object).

Method Detail

preprocess

ByteBuffer preprocess(Zxid zxid,
                    ByteBuffer message)

Converts a message to an idempotent transaction. This method is called only on the leader after the Zxid has been assigned but before proposing the message to followers.

Parameters:

zxid - zxid of the message.

message - the original message

Returns:

an idempotent state update based on the original message. This is what gets proposed to followers.

deliver

void deliver(Zxid zxid,
           ByteBuffer stateUpdate,
           String clientId,
           Object ctx)

Callback for Zab.send(java.nio.ByteBuffer, java.lang.Object). This method is called from a single thread to ensure that the state updates are applied in the same order as they arrived. Zab assumes that the transaction is successfully applied to the state machine when this method returns.

Parameters:

zxid - zxid of the message

stateUpdate - the incremental state update

clientId - the id of the client who sends the request. The request delivered in RECOVERING phase has clientId sets to null.

ctx - the context object.

flushed

void flushed(Zxid zxid,
           ByteBuffer flushRequest,
           Object ctx)

Callback for Zab.flush(java.nio.ByteBuffer, java.lang.Object). This method is called from the same thread as the deliver(com.github.zk1931.jzab.Zxid, java.nio.ByteBuffer, java.lang.String, java.lang.Object) callback.

Parameters:

flushRequest - the flush request.

ctx - the context object.

snapshotDone

void snapshotDone(String filePath,
                Object ctx)

Callback for Zab.takeSnapshot(java.lang.Object).

Parameters:

filePath - the path for the snapshot file.

ctx - the context object.

removed

void removed(String serverId,
           Object ctx)

Callback for Zab.remove(java.lang.String, java.lang.Object).

Parameters:

serverId - the ID of the server whom gets removed.

ctx - the context object.

save

void save(FileOutputStream fos)

Serializes the application state to a FileOutputStream.

Parameters:

fos - file to write the state to.

restore

void restore(FileInputStream fis)

Deserializes the application state from a FileInputStream.

Parameters:

fis - file to read the state from.

recovering

void recovering(PendingRequests pendingRequests)

Notifies the state machine that Zab is in recovering phase. When Zab goes from leading/following phase to recovering phase, there might be requests that have been submitted to Zab but haven't been delivered back to the state machine. These requests, along with their associated contexts, are passed backed to the state machine. Note that these requests might or might not have been committed by Zab.

Parameters:

pendingRequests - the pending requests, see PendingRequests.

leading

void leading(Set<String> activeFollowers,
           Set<String> clusterMembers)

Notifies the state machine that Zab is in leading phase with given sets of active followers and cluster members. This method gets called when Zab transitions from recovering phase to leading phase. It also gets called when there is a change in active followers or cluster membership while Zab is in leading phase. This method is called from the same thread as deliver(com.github.zk1931.jzab.Zxid, java.nio.ByteBuffer, java.lang.String, java.lang.Object).

Parameters:

activeFollowers - current alive followers.

clusterMembers - the members of new configuration.

following

void following(String leader,
             Set<String> clusterMembers)

Notifies the state machine that Zab is in following phase with given leader and cluster members. This method gets called when Zab transitions from recovering phase to following phase. It also gets called when there is a change in cluster membership while Zab is in following phase. This method is called from the same thread as deliver(com.github.zk1931.jzab.Zxid, java.nio.ByteBuffer, java.lang.String, java.lang.Object).

Parameters:

leader - current leader.

clusterMembers - the members of new configuration.