modules/fdbworkers/src/flash/tools/debugger/concrete/DMessageCache.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 flash.tools.debugger.concrete;

/**
 * This cache directly manages the creation/destruction of DMessages
 * by allowing DMessages to be re-used.
 * 
 * It has been observed that the Player send a tremendous number of
 * small (< 8Byte of data) messages and that by allocating a fixed
 * number of these, and then re-using them, we can assist the garbage
 * collector greatly.
 * 
 * The cache is arranged as an array whereby DMessages with 'index'
 * number of bytes for data are housed.  It is asssumed that at
 * any moment in time only one DMessage will be required and thus
 * this technique works.  If DMessages are to be stored for 
 * later processing (implying that many will exist at any moment)
 * then we need to implement a more sophisticated cache (probably
 * storing a Vector of DMessages at each index).
 *
 * Very large DMessages are currently not cached.
 * 
 * This is class is a singleton.
 */
public class DMessageCache
{
	public static final int MAX_CACHED_DATA_SIZE		= 128;  /* should consume around 4n + n(n+1)/2 bytes */

	/* our cache */
	static DMessage[] m_cache = new DMessage[MAX_CACHED_DATA_SIZE];

	/**
	 * Obtain a DMessage from the cache if possible, otherwise make one for me.
	 */
	public static DMessage alloc(int size)
	{
		DMessage msg;

		int index = size2Index(size);

		/**
		 * We see if this could possibly be found in our cache,
		 * if so, then see if there is one for us to use,
		 * otherwise create a new one 
		 */
		if (index < 0)
			msg = new DMessage(size);
		else if (m_cache[index] == null)
			msg = new DMessage(size);
        else
		{
			msg = m_cache[index];
			m_cache[index] = null;
		}

//		System.out.println("msgsize="+size+uft());
		return msg;
	}

	private static String uft()
	{
		Runtime rt = Runtime.getRuntime();
		long free = rt.freeMemory(), total = rt.totalMemory(), used =  total - free;
//		long max = rt.maxMemory();
		java.text.NumberFormat nf = java.text.NumberFormat.getInstance() ;
//        System.out.println("used: "+nf.format(used)+" free: "+nf.format(free)+" total: "+nf.format(total)+" max: "+nf.format(max));
        return ", used "+nf.format(used)+", free "+nf.format(free)+", total "+nf.format(total); //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
    }

	/**
	 * Put a DMessage into the cache for reuse
	 */
	public static void free(DMessage msg)
	{
		int index = size2Index(msg.getSize());

		msg.clear(); /* clear stuff up for re-use */

		/** 
		 * If it is too big we don't store cache, assuming
		 * the GC can do a better job than us at reusing the memory,
		 * Otherwise we put it in our cache
		 */
		if (index < 0)
			;
		else if (m_cache[index] != null)
			; /* bad => need to use a Vector in the array to house multiple DMessages */
		else
			m_cache[index] = msg;
	}

	public static int size2Index(int size) { return ((size < MAX_CACHED_DATA_SIZE) ? size : -1); }
//	public static int size2Index(int size) { return -1; }
}