com.lmax.disruptor.BatchEventProcessor Maven / Gradle / Ivy
/*
* Copyright 2011 LMAX Ltd.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.lmax.disruptor;
import java.util.concurrent.atomic.AtomicInteger;
/**
* Convenience class for handling the batching semantics of consuming entries from a {@link RingBuffer}
* and delegating the available events to an {@link EventHandler}.
*
* If the {@link EventHandler} also implements {@link LifecycleAware} it will be notified just after the thread
* is started and just before the thread is shutdown.
*
* @param event implementation storing the data for sharing during exchange or parallel coordination of an event.
*/
public final class BatchEventProcessor
implements EventProcessor
{
private static final int IDLE = 0;
private static final int HALTED = IDLE + 1;
private static final int RUNNING = HALTED + 1;
private final AtomicInteger running = new AtomicInteger(IDLE);
private ExceptionHandler exceptionHandler;
private final DataProvider dataProvider;
private final SequenceBarrier sequenceBarrier;
private final EventHandler eventHandler;
private final Sequence sequence = new Sequence(Sequencer.INITIAL_CURSOR_VALUE);
private final TimeoutHandler timeoutHandler;
private final BatchStartAware batchStartAware;
/**
* Construct a {@link EventProcessor} that will automatically track the progress by updating its sequence when
* the {@link EventHandler#onEvent(Object, long, boolean)} method returns.
*
* @param dataProvider to which events are published.
* @param sequenceBarrier on which it is waiting.
* @param eventHandler is the delegate to which events are dispatched.
*/
public BatchEventProcessor(
final DataProvider dataProvider,
final SequenceBarrier sequenceBarrier,
final EventHandler eventHandler)
{
this.dataProvider = dataProvider;
this.sequenceBarrier = sequenceBarrier;
this.eventHandler = eventHandler;
if (eventHandler instanceof SequenceReportingEventHandler)
{
((SequenceReportingEventHandler) eventHandler).setSequenceCallback(sequence);
}
batchStartAware =
(eventHandler instanceof BatchStartAware) ? (BatchStartAware) eventHandler : null;
timeoutHandler =
(eventHandler instanceof TimeoutHandler) ? (TimeoutHandler) eventHandler : null;
}
@Override
public Sequence getSequence()
{
return sequence;
}
@Override
public void halt()
{
running.set(HALTED);
sequenceBarrier.alert();
}
@Override
public boolean isRunning()
{
return running.get() != IDLE;
}
/**
* Set a new {@link ExceptionHandler} for handling exceptions propagated out of the {@link BatchEventProcessor}
*
* @param exceptionHandler to replace the existing exceptionHandler.
*/
public void setExceptionHandler(final ExceptionHandler exceptionHandler)
{
if (null == exceptionHandler)
{
throw new NullPointerException();
}
this.exceptionHandler = exceptionHandler;
}
/**
* It is ok to have another thread rerun this method after a halt().
*
* @throws IllegalStateException if this object instance is already running in a thread
*/
@Override
public void run()
{
if (running.compareAndSet(IDLE, RUNNING))
{
sequenceBarrier.clearAlert();
notifyStart();
try
{
if (running.get() == RUNNING)
{
processEvents();
}
}
finally
{
notifyShutdown();
running.set(IDLE);
}
}
else
{
// This is a little bit of guess work. The running state could of changed to HALTED by
// this point. However, Java does not have compareAndExchange which is the only way
// to get it exactly correct.
if (running.get() == RUNNING)
{
throw new IllegalStateException("Thread is already running");
}
else
{
earlyExit();
}
}
}
private void processEvents()
{
T event = null;
long nextSequence = sequence.get() + 1L;
while (true)
{
try
{
final long availableSequence = sequenceBarrier.waitFor(nextSequence);
if (batchStartAware != null)
{
batchStartAware.onBatchStart(availableSequence - nextSequence + 1);
}
while (nextSequence <= availableSequence)
{
event = dataProvider.get(nextSequence);
eventHandler.onEvent(event, nextSequence, nextSequence == availableSequence);
nextSequence++;
}
sequence.set(availableSequence);
}
catch (final TimeoutException e)
{
notifyTimeout(sequence.get());
}
catch (final AlertException ex)
{
if (running.get() != RUNNING)
{
break;
}
}
catch (final Throwable ex)
{
handleEventException(ex, nextSequence, event);
sequence.set(nextSequence);
nextSequence++;
}
}
}
private void earlyExit()
{
notifyStart();
notifyShutdown();
}
private void notifyTimeout(final long availableSequence)
{
try
{
if (timeoutHandler != null)
{
timeoutHandler.onTimeout(availableSequence);
}
}
catch (Throwable e)
{
handleEventException(e, availableSequence, null);
}
}
/**
* Notifies the EventHandler when this processor is starting up
*/
private void notifyStart()
{
if (eventHandler instanceof LifecycleAware)
{
try
{
((LifecycleAware) eventHandler).onStart();
}
catch (final Throwable ex)
{
handleOnStartException(ex);
}
}
}
/**
* Notifies the EventHandler immediately prior to this processor shutting down
*/
private void notifyShutdown()
{
if (eventHandler instanceof LifecycleAware)
{
try
{
((LifecycleAware) eventHandler).onShutdown();
}
catch (final Throwable ex)
{
handleOnShutdownException(ex);
}
}
}
/**
* Delegate to {@link ExceptionHandler#handleEventException(Throwable, long, Object)} on the delegate or
* the default {@link ExceptionHandler} if one has not been configured.
*/
private void handleEventException(final Throwable ex, final long sequence, final T event)
{
getExceptionHandler().handleEventException(ex, sequence, event);
}
/**
* Delegate to {@link ExceptionHandler#handleOnStartException(Throwable)} on the delegate or
* the default {@link ExceptionHandler} if one has not been configured.
*/
private void handleOnStartException(final Throwable ex)
{
getExceptionHandler().handleOnStartException(ex);
}
/**
* Delegate to {@link ExceptionHandler#handleOnShutdownException(Throwable)} on the delegate or
* the default {@link ExceptionHandler} if one has not been configured.
*/
private void handleOnShutdownException(final Throwable ex)
{
getExceptionHandler().handleOnShutdownException(ex);
}
private ExceptionHandler getExceptionHandler()
{
ExceptionHandler handler = exceptionHandler;
if (handler == null)
{
return ExceptionHandlers.defaultHandler();
}
return handler;
}
}