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/*
* Copyright 2008-2017 UnboundID Corp.
* All Rights Reserved.
*/
/*
* Copyright (C) 2008-2017 UnboundID Corp.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License (GPLv2 only)
* or the terms of the GNU Lesser General Public License (LGPLv2.1 only)
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see .
*/
package com.unboundid.util.parallel;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;
import com.unboundid.util.Debug;
import com.unboundid.util.InternalUseOnly;
import com.unboundid.util.ThreadSafety;
import com.unboundid.util.ThreadSafetyLevel;
/**
* This class provides an asynchronous mechanism to do parallel processing of
* items that undergo identical processing. It can be used as part of a
* pipeline where input items are submitted without waiting for them to
* complete. To prevent a backlog of input or output items, a maximum
* capacity should be set on the {@code pendingQueue} and {@code outputQueue}
* if one is used.
*
* The {@link ParallelProcessor} passed into the constructor is wholly owned
* by this instance. It should not be used elsewhere after constructing this
* instance. It will be shut down when this instance's {@code shutdown()}
* method is called.
*
* When this AsynchronousParallelProcessor is no longer needed, {@code shutdown}
* must be called to terminate all worker threads.
*
* This class is intended to only be used internally by the SDK.
*
* @param The type of the input items of {@code processAll}.
* @param The type of the output items of {@code processAll}.
*/
@InternalUseOnly()
@ThreadSafety(level=ThreadSafetyLevel.COMPLETELY_THREADSAFE)
public final class AsynchronousParallelProcessor
{
// Queue of input items.
private final BlockingQueue pendingQueue;
// The ParallelProcessor that is used to process the input items.
private final ParallelProcessor parallelProcessor;
// Processor for the results.
private final ResultProcessor resultProcessor;
// Thread that pulls items from pendingQueue, passes them to
// parallelProcessor, and processes the results.
private final InvokerThread invokerThread;
// Set to true when this is shutdown.
private final AtomicBoolean shutdown = new AtomicBoolean(false);
// Set by worker threads to signal that there was a problem during processing.
// Once this is set, all calls to submit() will fail with this exception.
private final AtomicReference invocationException =
new AtomicReference();
/**
* Constructs a new AsynchronousParallelProcessor with the specified
* parameters.
*
* @param pendingQueue The queue where pending input items will be stored.
* If processing of input items cannot keep up with the
* rate that they are submitted, then this queue can grow
* without bound unless it was created with a maximum
* capacity. This queue must be used exclusively by this
* instance.
* @param parallelProcessor The ParallelProcessor that is used to process
* the submitted input items. It must be used
* exclusively by this instance. When this instance
* is shutdown, the ParallelProcessor will be
* shutdown too.
* @param resultProcessor The ResultProcessor that is invoked sequentially
* for each result.
*/
public AsynchronousParallelProcessor(
final BlockingQueue pendingQueue,
final ParallelProcessor parallelProcessor,
final ResultProcessor resultProcessor)
{
this.pendingQueue = pendingQueue;
this.parallelProcessor = parallelProcessor;
this.resultProcessor = resultProcessor;
this.invokerThread = new InvokerThread();
this.invokerThread.start();
}
/**
* Constructs a new AsynchronousParallelProcessor with the specified
* parameters.
*
* @param pendingQueue The queue where pending input items will be stored.
* If processing of input items cannot keep up with the
* rate that they are submitted, then this queue can grow
* without bound unless it was created with a maximum
* capacity. This queue must be used exclusively by this
* instance.
* @param parallelProcessor The ParallelProcessor that is used to process
* the submitted input items. It must be used
* exclusively by this instance. When this instance
* is shutdown, the ParallelProcessor will be
* shutdown too.
* @param outputQueue The output queue where results will be submitted
* sequentially in the order that they were submitted.
* If the queue has maximum capacity, then processing
* will cease while waiting for capacity in the queue.
*/
public AsynchronousParallelProcessor(
final BlockingQueue pendingQueue,
final ParallelProcessor parallelProcessor,
final BlockingQueue> outputQueue)
{
this(pendingQueue, parallelProcessor,
new OutputEnqueuer(outputQueue));
}
/**
* Submits the specified item for processing, waiting if necessary for
* room in the pendingQueue.
*
* @param input The input item to process. It must not be {@code null}.
*
* @throws InterruptedException If this thread is interrupted during
* processing.
*/
public synchronized void submit(final I input)
throws InterruptedException
{
if (shutdown.get())
{
throw new IllegalStateException("cannot call submit() after shutdown()");
}
final Throwable resultProcessingError = invocationException.get();
if (resultProcessingError != null)
{
shutdown();
throw new RuntimeException(resultProcessingError);
}
pendingQueue.put(input);
}
/**
* Shuts this down. This includes waiting for all worker threads to
* finish. Processing of all input items will complete before this call
* returns. It is not an error to call {@code shutdown()} more than once,
* but it is an error to call {@code submit()} after {@code shutdown()} has
* been called.
*
* @throws InterruptedException If this thread is interrupted during
* processing.
*/
public synchronized void shutdown()
throws InterruptedException
{
if (shutdown.getAndSet(true))
{
// Already shut down.
return;
}
// The invoker thread will not exit until it has completed all
// of the pending items.
invokerThread.join();
parallelProcessor.shutdown();
}
/**
* ResultProcessor implementation that enqueues results.
*
* @param The type of the input items of {@code processAll}.
* @param The type of the output items of {@code processAll}.
*/
private static final class OutputEnqueuer
implements ResultProcessor
{
private final BlockingQueue> outputQueue;
/**
* Constructor.
*
* @param outputQueue The queue where results will be enqueued.
*/
private OutputEnqueuer(final BlockingQueue> outputQueue)
{
this.outputQueue = outputQueue;
}
/**
* {@inheritDoc}
*/
public void processResult(final Result ioResult)
throws Exception
{
outputQueue.put(ioResult);
}
}
/**
* This thread pulls items from pendingQueue, processes them in parallel,
* and passes the results to resultProcessor. And then does it all over again
* until it's shutdown and there is no more to process.
*/
private final class InvokerThread
extends Thread
{
/**
* Constructor.
*/
private InvokerThread()
{
super("Asynchronous Parallel Processor");
setDaemon(true);
}
/**
* Pulls items from pendingQueue, processes them in parallel,
* and passes the results to resultProcessor. And then does it all over
* again until it's shutdown and there is no more to process.
*/
@Override()
public void run()
{
while (!(shutdown.get() && pendingQueue.isEmpty()))
{
try
{
final I item = pendingQueue.poll(100, TimeUnit.MILLISECONDS);
if (item != null)
{
final List items = new ArrayList(1 + pendingQueue.size());
items.add(item);
pendingQueue.drainTo(items);
final List> results =
parallelProcessor.processAll(items);
for (final Result result : results)
{
resultProcessor.processResult(result);
}
}
}
catch (Throwable e)
{
Debug.debugException(e);
// It's in the contract of this class that nothing in this try
// block should throw an exception under normal operating conditions.
// So if we ever catch something here, then we treat that it as
// a terminating condition. This thread will continue to run to
// drain any remaining items from the queue, so that we can shutdown
// reasonably cleanly. However, we will not accept any new input
// item submissions. That is, future calls to submit() will force
// a shutdown and then throw an Exception, which includes e as the
// original cause. We use compareAndSet so that we only keep track
// of the first caught exception.
invocationException.compareAndSet(null, e);
}
}
}
}
}
