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/*
 * This file is part of Log4Jdbc.
 *
 * Log4Jdbc is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Log4Jdbc 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 Log4Jdbc.  If not, see .
 *
 */
package fr.ms.log4jdbc.thread;

import java.util.Collections;
import java.util.LinkedList;
import java.util.List;

import fr.ms.log4jdbc.utils.Log4JdbcProperties;

/**
 *
 * @see Marco4J
 *
 *
 * @author Marco Semiao
 *
 */
public class SingleThreadPoolExecutor {

    private final static SingleThreadPoolExecutor INSTANCE = new SingleThreadPoolExecutor();
    private final static Log4JdbcProperties props = Log4JdbcProperties.getInstance();

    private final WorkerRunnable w = new WorkerRunnable();

    private final Thread thread;

    private SingleThreadPoolExecutor() {
	thread = new Thread(w, "Log4Jdbc-Logger");
	thread.setDaemon(true);
	thread.setPriority(Thread.MIN_PRIORITY);
	thread.start();
    }

    public static SingleThreadPoolExecutor getInstance() {
	return INSTANCE;
    }

    public synchronized void execute(final Runnable command) {
	final int limit = props.logProcessThreadSize();

	final int size = w.pool.size();

	if (size > limit && thread.getPriority() != Thread.MAX_PRIORITY) {

	    if (Thread.MAX_PRIORITY != thread.getPriority()) {
		thread.setPriority(Thread.MAX_PRIORITY);
	    }
	    logLimit();
	} else if (size > (limit / 2) && thread.getPriority() == Thread.MIN_PRIORITY) {
	    if (Thread.NORM_PRIORITY != thread.getPriority()) {
		thread.setPriority(Thread.NORM_PRIORITY);
		logLimit();
	    }
	} else if (size < (limit / 10)) {
	    if (Thread.MIN_PRIORITY != thread.getPriority()) {
		thread.setPriority(Thread.MIN_PRIORITY);
		logLimit();
	    }
	}

	w.execute(command);
    }

    private void logLimit() {
	if (props.logProcessThreadDebug()) {
	    System.out.println("Log4JDBC : pool size limit : " + w.pool.size() + " - thread priority  : " + thread.getPriority());
	}
    }

    private static class WorkerRunnable implements Runnable {

	private final Verrou v = new Verrou();

	private final List pool = Collections.synchronizedList(new LinkedList());

	public void run() {
	    while (true) {
		if (pool.isEmpty()) {
		    v.attente();
		} else {
		    final Runnable r = getNextRunnable();
		    try {
			if (r != null) {
			    r.run();
			}
		    } catch (final Throwable t) {
			t.printStackTrace();
		    }
		}
	    }
	}

	public void execute(final Runnable command) {
	    pool.add(command);
	    v.libere();
	}

	private Runnable getNextRunnable() {
	    final Runnable r = (Runnable) pool.get(0);
	    pool.remove(0);
	    return r;
	}
    }

    private static class Verrou {

	public void attente() {
	    pose(false);
	}

	public void libere() {
	    pose(true);
	}

	private synchronized void pose(final boolean libere) {
	    if (libere) {
		notify();
	    } else {
		try {
		    wait();
		} catch (final InterruptedException e) {
		    e.printStackTrace();
		}
	    }
	}
    }
}