Module com.lmax.disruptor

Package com.lmax.disruptor

Interface EventHandler<T>

Type Parameters:

T - event implementation storing the data for sharing during exchange or parallel coordination of an event.

All Superinterfaces:

EventHandlerIdentity

All Known Implementing Classes:

AggregateEventHandler

public interface EventHandler<T>

Callback interface to be implemented for processing events as they become available in the RingBuffer

See Also:

if you want to handle exceptions propagated out of the handler.

Method Summary

Modifier and Type	Method	Description
default void	onBatchStart(long batchSize, long queueDepth)	Invoked by BatchEventProcessor prior to processing a batch of events
void	onEvent(T event, long sequence, boolean endOfBatch)	Called when a publisher has published an event to the RingBuffer.
default void	onShutdown()	Called once just before the event processing thread is shutdown.
default void	onStart()	Called once on thread start before first event is available.
default void	onTimeout(long sequence)	Invoked when a BatchEventProcessor's WaitStrategy throws a TimeoutException.
default void	setSequenceCallback(Sequence sequenceCallback)	Used by the BatchEventProcessor to set a callback allowing the EventHandler to notify when it has finished consuming an event if this happens after the onEvent(Object, long, boolean) call.

Method Detail

onEvent

void onEvent(T event,
             long sequence,
             boolean endOfBatch)
      throws java.lang.Exception

Called when a publisher has published an event to the RingBuffer. The BatchEventProcessor will read messages from the RingBuffer in batches, where a batch is all of the events available to be processed without having to wait for any new event to arrive. This can be useful for event handlers that need to do slower operations like I/O as they can group together the data from multiple events into a single operation. Implementations should ensure that the operation is always performed when endOfBatch is true as the time between that message and the next one is indeterminate.

Parameters:

event - published to the RingBuffer

sequence - of the event being processed

endOfBatch - flag to indicate if this is the last event in a batch from the RingBuffer

Throws:

java.lang.Exception - if the EventHandler would like the exception handled further up the chain.

setSequenceCallback

default void setSequenceCallback(Sequence sequenceCallback)

Used by the BatchEventProcessor to set a callback allowing the EventHandler to notify when it has finished consuming an event if this happens after the onEvent(Object, long, boolean) call.

Typically this would be used when the handler is performing some sort of batching operation such as writing to an IO device; after the operation has completed, the implementation should call Sequence.set(long) to update the sequence and allow other processes that are dependent on this handler to progress.

Parameters:

sequenceCallback - callback on which to notify the BatchEventProcessor that the sequence has progressed.

onBatchStart

default void onBatchStart(long batchSize,
                          long queueDepth)

Invoked by BatchEventProcessor prior to processing a batch of events

Parameters:

batchSize - the size of the batch that is starting

queueDepth - the total number of queued up events including the batch about to be processed

onStart

default void onStart()

Called once on thread start before first event is available.

onShutdown

default void onShutdown()

Called once just before the event processing thread is shutdown.

Sequence event processing will already have stopped before this method is called. No events will be processed after this message.

onTimeout

default void onTimeout(long sequence)
                throws java.lang.Exception

Invoked when a BatchEventProcessor's WaitStrategy throws a TimeoutException.

Parameters:

sequence - - the last processed sequence.

Throws:

java.lang.Exception - if the implementation is unable to handle this timeout.