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The official Couchbase JVM Core IO Library
/*
* 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.couchbase.client.deps.com.lmax.disruptor;
import com.couchbase.client.deps.com.lmax.disruptor.util.Util;
import java.util.concurrent.Executor;
import java.util.concurrent.atomic.AtomicBoolean;
/**
* WorkerPool contains a pool of {@link WorkProcessor}s that will consume sequences so jobs can be farmed out across a pool of workers.
* Each of the {@link WorkProcessor}s manage and calls a {@link WorkHandler} to process the events.
*
* @param event to be processed by a pool of workers
*/
public final class WorkerPool
{
private final AtomicBoolean started = new AtomicBoolean(false);
private final Sequence workSequence = new Sequence(Sequencer.INITIAL_CURSOR_VALUE);
private final RingBuffer ringBuffer;
// WorkProcessors are created to wrap each of the provided WorkHandlers
private final WorkProcessor[] workProcessors;
/**
* Create a worker pool to enable an array of {@link WorkHandler}s to consume published sequences.
*
* This option requires a pre-configured {@link RingBuffer} which must have {@link RingBuffer#addGatingSequences(Sequence...)}
* called before the work pool is started.
*
* @param ringBuffer of events to be consumed.
* @param sequenceBarrier on which the workers will depend.
* @param exceptionHandler to callback when an error occurs which is not handled by the {@link WorkHandler}s.
* @param workHandlers to distribute the work load across.
*/
public WorkerPool(final RingBuffer ringBuffer,
final SequenceBarrier sequenceBarrier,
final ExceptionHandler exceptionHandler,
final WorkHandler... workHandlers)
{
this.ringBuffer = ringBuffer;
final int numWorkers = workHandlers.length;
workProcessors = new WorkProcessor[numWorkers];
for (int i = 0; i < numWorkers; i++)
{
workProcessors[i] = new WorkProcessor(ringBuffer,
sequenceBarrier,
workHandlers[i],
exceptionHandler,
workSequence);
}
}
/**
* Construct a work pool with an internal {@link RingBuffer} for convenience.
*
* This option does not require {@link RingBuffer#addGatingSequences(Sequence...)} to be called before the work pool is started.
*
* @param eventFactory for filling the {@link RingBuffer}
* @param exceptionHandler to callback when an error occurs which is not handled by the {@link WorkHandler}s.
* @param workHandlers to distribute the work load across.
*/
public WorkerPool(final EventFactory eventFactory,
final ExceptionHandler exceptionHandler,
final WorkHandler... workHandlers)
{
ringBuffer = RingBuffer.createMultiProducer(eventFactory, 1024, new BlockingWaitStrategy());
final SequenceBarrier barrier = ringBuffer.newBarrier();
final int numWorkers = workHandlers.length;
workProcessors = new WorkProcessor[numWorkers];
for (int i = 0; i < numWorkers; i++)
{
workProcessors[i] = new WorkProcessor(ringBuffer,
barrier,
workHandlers[i],
exceptionHandler,
workSequence);
}
ringBuffer.addGatingSequences(getWorkerSequences());
}
/**
* Get an array of {@link Sequence}s representing the progress of the workers.
*
* @return an array of {@link Sequence}s representing the progress of the workers.
*/
public Sequence[] getWorkerSequences()
{
final Sequence[] sequences = new Sequence[workProcessors.length + 1];
for (int i = 0, size = workProcessors.length; i < size; i++)
{
sequences[i] = workProcessors[i].getSequence();
}
sequences[sequences.length - 1] = workSequence;
return sequences;
}
/**
* Start the worker pool processing events in sequence.
*
* @param executor providing threads for running the workers.
* @return the {@link RingBuffer} used for the work queue.
* @throws IllegalStateException if the pool has already been started and not halted yet
*/
public RingBuffer start(final Executor executor)
{
if (!started.compareAndSet(false, true))
{
throw new IllegalStateException("WorkerPool has already been started and cannot be restarted until halted.");
}
final long cursor = ringBuffer.getCursor();
workSequence.set(cursor);
for (WorkProcessor processor : workProcessors)
{
processor.getSequence().set(cursor);
executor.execute(processor);
}
return ringBuffer;
}
/**
* Wait for the {@link RingBuffer} to drain of published events then halt the workers.
*/
public void drainAndHalt()
{
Sequence[] workerSequences = getWorkerSequences();
while (ringBuffer.getCursor() > Util.getMinimumSequence(workerSequences))
{
Thread.yield();
}
for (WorkProcessor processor : workProcessors)
{
processor.halt();
}
started.set(false);
}
/**
* Halt all workers immediately at the end of their current cycle.
*/
public void halt()
{
for (WorkProcessor processor : workProcessors)
{
processor.halt();
}
started.set(false);
}
public boolean isRunning()
{
return started.get();
}
}