softreferencegrammarpool.java

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/*
 * Copyright 2005 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.
 */

package com.sun.org.apache.xerces.internal.jaxp.validation;

import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;

import com.sun.org.apache.xerces.internal.xni.grammars.Grammar;
import com.sun.org.apache.xerces.internal.xni.grammars.XMLGrammarDescription;
import com.sun.org.apache.xerces.internal.xni.grammars.XMLSchemaDescription;
import com.sun.org.apache.xerces.internal.xni.grammars.XMLGrammarPool;

/**
 * <p>This grammar pool is a memory sensitive cache. The grammars
 * stored in the pool are softly reachable and may be cleared by
 * the garbage collector in response to memory demand. Equality
 * of <code>XMLSchemaDescription</code>s is determined using both
 * the target namespace for the schema and schema location.</p>
 * 
 * @author Michael Glavassevich, IBM
 * @version $Id: SoftReferenceGrammarPool.java,v 1.1.4.1 2005/09/05 11:43:19 sunithareddy Exp $
 */
final class SoftReferenceGrammarPool implements XMLGrammarPool {
    
    //
    // Constants
    //
    
    /** Default size. */
    protected static final int TABLE_SIZE = 11;
    
    /** Zero length grammar array. */
    protected static final Grammar [] ZERO_LENGTH_GRAMMAR_ARRAY = new Grammar [0];
    
    //
    // Data
    //
    
    /** Grammars. */
    protected Entry [] fGrammars = null;
    
    /** Flag indicating whether this pool is locked */
    protected boolean fPoolIsLocked;
    
    /** The number of grammars in the pool */
    protected int fGrammarCount = 0;
    
    /** Reference queue for cleared grammar references */
    protected final ReferenceQueue fReferenceQueue = new ReferenceQueue();
    
    //
    // Constructors
    //
    
    /** Constructs a grammar pool with a default number of buckets. */
    public SoftReferenceGrammarPool() {
        fGrammars = new Entry[TABLE_SIZE];
        fPoolIsLocked = false;
    } // <init>()
    
    /** Constructs a grammar pool with a specified number of buckets. */
    public SoftReferenceGrammarPool(int initialCapacity) {
        fGrammars = new Entry[initialCapacity];
        fPoolIsLocked = false;
    }
    
    //
    // XMLGrammarPool methods
    //
    
    /* <p> Retrieve the initial known set of grammars. This method is
     * called by a validator before the validation starts. The application
     * can provide an initial set of grammars available to the current
     * validation attempt. </p>
     *
     * @param grammarType The type of the grammar, from the
     *  		  <code>com.sun.org.apache.xerces.internal.xni.grammars.XMLGrammarDescription</code>
     *  		  interface.
     * @return 		  The set of grammars the validator may put in its "bucket"
     */
    public Grammar [] retrieveInitialGrammarSet (String grammarType) {
        synchronized (fGrammars) {
            clean();
            // Return no grammars. This allows the garbage collector to sift
            // out grammars which are not in use when memory demand is high.
            // It also allows the pool to return the "right" schema grammar
            // based on schema locations.
            return ZERO_LENGTH_GRAMMAR_ARRAY;
        }
    } // retrieveInitialGrammarSet (String): Grammar[]
    
    /* <p> Return the final set of grammars that the validator ended up
     * with. This method is called after the validation finishes. The
     * application may then choose to cache some of the returned grammars.</p>
     * <p>In this implementation, we make our choice based on whether this object
     * is "locked"--that is, whether the application has instructed
     * us not to accept any new grammars.</p>
     *
     * @param grammarType The type of the grammars being returned;
     * @param grammars 	  An array containing the set of grammars being
     *  		  returned; order is not significant.
     */
    public void cacheGrammars(String grammarType, Grammar[] grammars) {
        if (!fPoolIsLocked) {
            for (int i = 0; i < grammars.length; ++i) {
                putGrammar(grammars[i]);
            }
        }
    } // cacheGrammars(String, Grammar[]);
    
    /* <p> This method requests that the application retrieve a grammar
     * corresponding to the given GrammarIdentifier from its cache.
     * If it cannot do so it must return null; the parser will then
     * call the EntityResolver. </p>
     * <strong>An application must not call its EntityResolver itself
     * from this method; this may result in infinite recursions.</strong>
     *
     * This implementation chooses to use the root element name to identify a DTD grammar
     * and the target namespace to identify a Schema grammar.
     *
     * @param desc The description of the Grammar being requested.
     * @return     The Grammar corresponding to this description or null if
     *  	   no such Grammar is known.
     */
    public Grammar retrieveGrammar(XMLGrammarDescription desc) {
        return getGrammar(desc);
    } // retrieveGrammar(XMLGrammarDescription):  Grammar
    
    //
    // Public methods
    //
    
    /**
     * Puts the specified grammar into the grammar pool and associates it to
     * its root element name or its target namespace.
     *
     * @param grammar The Grammar.
     */
    public void putGrammar(Grammar grammar) {
        if (!fPoolIsLocked) {
            synchronized (fGrammars) {
                clean();
                XMLGrammarDescription desc = grammar.getGrammarDescription();
                int hash = hashCode(desc);
                int index = (hash & 0x7FFFFFFF) % fGrammars.length;
                for (Entry entry = fGrammars[index]; entry != null; entry = entry.next) {
                    if (entry.hash == hash && equals(entry.desc, desc)) {
                        if (entry.grammar.get() != grammar) {
                            entry.grammar = new SoftGrammarReference(entry, grammar, fReferenceQueue);
                        }
                        return;
                    }
                }
                // create a new entry
                Entry entry = new Entry(hash, index, desc, grammar, fGrammars[index], fReferenceQueue);
                fGrammars[index] = entry;
                fGrammarCount++;
            }
        }
    } // putGrammar(Grammar)
    
    /**
     * Returns the grammar associated to the specified grammar description.
     * Currently, the root element name is used as the key for DTD grammars
     * and the target namespace  is used as the key for Schema grammars.
     *
     * @param desc The Grammar Description.
     */
    public Grammar getGrammar(XMLGrammarDescription desc) {
        synchronized (fGrammars) {
            clean();
            int hash = hashCode(desc);
            int index = (hash & 0x7FFFFFFF) % fGrammars.length;
            for (Entry entry = fGrammars[index]; entry != null; entry = entry.next) {
                Grammar tempGrammar = (Grammar) entry.grammar.get();
                /** If the soft reference has been cleared, remove this entry from the pool. */
                if (tempGrammar == null) {
                    removeEntry(entry);
                }
                else if ((entry.hash == hash) && equals(entry.desc, desc)) {
                    return tempGrammar;
                }
            }
            return null;
        }
    } // getGrammar(XMLGrammarDescription):Grammar
    
    /**
     * Removes the grammar associated to the specified grammar description from the
     * grammar pool and returns the removed grammar. Currently, the root element name
     * is used as the key for DTD grammars and the target namespace  is used
     * as the key for Schema grammars.
     *
     * @param desc The Grammar Description.
     * @return     The removed grammar.
     */
    public Grammar removeGrammar(XMLGrammarDescription desc) {
        synchronized (fGrammars) {
            clean();
            int hash = hashCode(desc);
            int index = (hash & 0x7FFFFFFF) % fGrammars.length;
            for (Entry entry = fGrammars[index]; entry != null; entry = entry.next) {