org.axonframework.eventhandling.tokenstore

Interface TokenStore

All Known Implementing Classes:

InMemoryTokenStore, JdbcTokenStore, JpaTokenStore, MongoTokenStore

public interface TokenStore

Describes a component capable of storing and retrieving event tracking tokens. An EventProcessor that is tracking an event stream can use the store to keep track of its position in the event stream. Tokens are stored by process name and segment index, enabling the same processor to be distributed over multiple processes or machines.

Author:

Rene de Waele, Allard Buijze

Method Summary

Modifier and Type	Method and Description
default void	extendClaim(String processorName, int segment) Extends the claim on the current token held by the this node for the given processorName and segment.
int[]	fetchSegments(String processorName) Returns an array of known segments for a given processorName.
TrackingToken	fetchToken(String processorName, int segment) Returns the last stored token for the given processorName and segment.
default void	initializeTokenSegments(String processorName, int segmentCount) Initializes the given segmentCount number of segments for the given processorName to track its tokens.
void	releaseClaim(String processorName, int segment) Release a claim of the token for given processorName and segment.
void	storeToken(TrackingToken token, String processorName, int segment) Stores the given token in the store.

Method Detail

initializeTokenSegments

default void initializeTokenSegments(String processorName,
                                     int segmentCount)
                              throws UnableToClaimTokenException

Initializes the given segmentCount number of segments for the given processorName to track its tokens. This method should only be invoked when no tokens have been stored for the given processor, yet.

This method will initialize the tokens, but no claim them. It will create the segments ranging from 0 until segmentCount - 1.

The exact behavior when this method is called while tokens were already present, is undefined in case the token already present is not owned by the initializing process.

Parameters:

processorName - The name of the processor to initialize segments for

segmentCount - The number of segments to initialize

Throws:

UnableToClaimTokenException - when a segment has already been created

storeToken

void storeToken(TrackingToken token,
                String processorName,
                int segment)
         throws UnableToClaimTokenException

Stores the given token in the store. The token marks the current position of the process with given processorName and segment. The given token may be null.

Any claims made by the current process have their timestamp updated.

Parameters:

token - The token to store for a given process and segment. May be null.

processorName - The name of the process for which to store the token

segment - The index of the segment for which to store the token

Throws:

UnableToClaimTokenException - when the token being updated has been claimed by another process.

fetchToken

TrackingToken fetchToken(String processorName,
                         int segment)
                  throws UnableToClaimTokenException

Returns the last stored token for the given processorName and segment. Returns null if the store holds no token or if the stored token for the given process and segment is null.

The token will be claimed by the current process (JVM instance), preventing access by other instances. To release the claim, use releaseClaim(String, int)

Parameters:

processorName - The process name for which to fetch the token

segment - The segment index for which to fetch the token

Returns:

The last stored TrackingToken or null if the store holds no token for given process and segment

Throws:

UnableToClaimTokenException - if there is a token for given processorName and segment, but they are claimed by another process.

extendClaim

default void extendClaim(String processorName,
                         int segment)
                  throws UnableToClaimTokenException

Extends the claim on the current token held by the this node for the given processorName and segment.

Parameters:

processorName - The process name for which to fetch the token

segment - The segment index for which to fetch the token

Throws:

UnableToClaimTokenException - if there is no token for given processorName and segment, or if it has been claimed by another process.

releaseClaim

void releaseClaim(String processorName,
                  int segment)

Release a claim of the token for given processorName and segment. If no such claim existed, nothing happens.

The caller must ensure not to use any streams opened based on the token for which the claim is released.

Parameters:

processorName - The name of the process owning the token (e.g. a TrackingEventProcessor name)

segment - the segment for which a token was obtained

fetchSegments

int[] fetchSegments(String processorName)

Returns an array of known segments for a given processorName.

The segments returned are segments for which a token has been stored previously. When the TokenStore is empty, an empty array is returned.

Parameters:

processorName - The process name for which to fetch the segments

Returns:

an array of segment identifiers.