/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * Copyright (c) 2010, Red Hat, Inc. and/or its affiliates or third-party contributors as
 * indicated by the @author tags or express copyright attribution
 * statements applied by the authors.  All third-party contributions are
 * distributed under license by Red Hat, Inc.
 *
 * This copyrighted material is made available to anyone wishing to use, modify,
 * copy, or redistribute it subject to the terms and conditions of the GNU
 * Lesser General Public License, 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 Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution; if not, write to:
 * Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor
 * Boston, MA  02110-1301  USA
 */
package org.hibernate.search.batchindexing.impl;

import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.RejectedExecutionHandler;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

import org.hibernate.search.util.logging.impl.LoggerFactory;
import org.hibernate.search.util.logging.impl.Log;

/**
 * Helper class to create threads;
 * these threads are grouped and named to be identified in a profiler.
 *
 * @author Sanne Grinovero
 */
public final class Executors {

	public static final int QUEUE_MAX_LENGTH = 1000;
	private static final String THREAD_GROUP_PREFIX = "Hibernate Search: ";

	private static final Log log = LoggerFactory.make();

	private Executors() {
		//now allowed
	}

	/**
	 * Creates a new fixed size ThreadPoolExecutor.
	 * It's using a blockingqueue of maximum 1000 elements and the rejection
	 * policy is set to CallerRunsPolicy for the case the queue is full.
	 * These settings are required to cap the queue, to make sure the
	 * timeouts are reasonable for most jobs.
	 *
	 * @param threads the number of threads
	 * @param groupname a label to identify the threadpool; useful for profiling.
	 * @return the new ExecutorService
	 */
	public static ThreadPoolExecutor newFixedThreadPool(int threads, String groupname) {
		return newFixedThreadPool( threads, groupname, QUEUE_MAX_LENGTH );
	}

	/**
	 * Creates a new fixed size ThreadPoolExecutor
	 *
	 * @param threads the number of threads
	 * @param groupname a label to identify the threadpool; useful for profiling.
	 * @param queueSize the size of the queue to store Runnables when all threads are busy
	 * @return the new ExecutorService
	 */
	public static ThreadPoolExecutor newFixedThreadPool(int threads, String groupname, int queueSize) {
		return new ThreadPoolExecutor(
				threads,
				threads,
				0L,
				TimeUnit.MILLISECONDS,
				new LinkedBlockingQueue<Runnable>( queueSize ),
				new SearchThreadFactory( groupname ),
				new BlockPolicy()
				);
	}

	/**
	 * The thread factory, used to customize thread names
	 */
	private static class SearchThreadFactory implements ThreadFactory {

		final ThreadGroup group;
		final AtomicInteger threadNumber = new AtomicInteger( 1 );
		final String namePrefix;

		SearchThreadFactory(String groupname) {
			SecurityManager s = System.getSecurityManager();
			group = ( s != null ) ? s.getThreadGroup() : Thread.currentThread().getThreadGroup();
			namePrefix = THREAD_GROUP_PREFIX + groupname + "-";
		}

		@Override
		public Thread newThread(Runnable r) {
			Thread t = new Thread( group, r, namePrefix + threadNumber.getAndIncrement(), 0 );
			return t;
		}

	}

	/**
	 * A handler for rejected tasks that will have the caller block until space is available.
	 */
	public static class BlockPolicy implements RejectedExecutionHandler {

		/**
		 * Creates a <tt>BlockPolicy</tt>.
		 */
		public BlockPolicy() {
		}

		/**
		 * Puts the Runnable to the blocking queue, effectively blocking the delegating thread until space is available.
		 *
		 * @param r the runnable task requested to be executed
		 * @param e the executor attempting to execute this task
		 */
		@Override
		public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
			try {
				e.getQueue().put( r );
			}
			catch (InterruptedException e1) {
				log.interruptedWorkError( r );
				Thread.currentThread().interrupt();
			}
		}
	}

}
