simplepool.java

velocity 的脚本语言的全部代码集合

package org.apache.velocity.util;

/*
 * Copyright 1999-2001,2004 The Apache Software Foundation.
 * 
 * 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.
 */

/**
 * Simple object pool. Based on ThreadPool and few other classes
 *
 * The pool will ignore overflow and return null if empty.
 *
 * @author Gal Shachor
 * @author Costin
 * @author <a href="mailto:[e-mail]">Geir Magnusson Jr.</a>
 * @version $Id: SimplePool.java,v 1.2.14.1 2004/03/03 23:23:07 geirm Exp $
 */
public final class SimplePool  
{
    /*
     * Where the objects are held.
     */
    private Object pool[];

    /**
     *  max amount of objects to be managed
     *  set via CTOR
     */
    private int max;    
    
    /**
     *  index of previous to next
     *  free slot
     */
    private int current=-1;
       
    public SimplePool(int max) 
    {
        this.max = max;
        pool = new Object[max];
    } 

    /**
     * Add the object to the pool, silent nothing if the pool is full
     */
    public void put(Object o) 
    {
        int idx=-1;
     
        synchronized( this ) 
        {
            /*
             *  if we aren't full
             */

            if( current < max - 1 )
            {
                /*
                 *  then increment the 
                 *  current index.
                 */
                idx = ++current;
            }

            if( idx >= 0 ) 
            {
                pool[idx] = o;
            }
        }
    }

    /**
     * Get an object from the pool, null if the pool is empty.
     */
    public  Object get() 
    {
        int idx = -1;
        
        synchronized( this ) 
        {
            /*
             *  if we have any in the pool
             */
            if( current >= 0 )
            {
                /*
                 *  take one out, so to speak -
                 *  separate the two operations
                 *  to make it clear that you
                 *  don't want idx = --current; :)
                 */

                idx = current;
                current--;
               
                /*
                 *  and since current was >= 0
                 *  to get in here, idx must be as well
                 *  so save the if() opration
                 */

                return pool[idx];
            }
        }
        
        return null;
    }

    /** Return the size of the pool
     */
    public int getMax() 
    {
        return max;
    }
}