classcache.java

java中比较著名的js引擎当属mozilla开源的rhino

/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Rhino code, released
 * May 6, 1999.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1997-1999
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Igor Bukanov, [e-mail]
 *
 * Alternatively, the contents of this file may be used under the terms of
 * the GNU General Public License Version 2 or later (the "GPL"), in which
 * case the provisions of the GPL are applicable instead of those above. If
 * you wish to allow use of your version of this file only under the terms of
 * the GPL and not to allow others to use your version of this file under the
 * MPL, indicate your decision by deleting the provisions above and replacing
 * them with the notice and other provisions required by the GPL. If you do
 * not delete the provisions above, a recipient may use your version of this
 * file under either the MPL or the GPL.
 *
 * ***** END LICENSE BLOCK ***** */

package org.mozilla.javascript;

import java.util.Hashtable;

/**
 * Cache of generated classes and data structures to access Java runtime
 * from JavaScript.
 *
 * @author Igor Bukanov
 *
 * @since Rhino 1.5 Release 5
 */
public class ClassCache
{
    private static final Object AKEY = new Object();

    private volatile boolean cachingIsEnabled = true;

    Hashtable classTable = new Hashtable();

    Hashtable javaAdapterGeneratedClasses = new Hashtable();

    ScriptableObject scope;

    private Hashtable interfaceAdapterCache;

    private int generatedClassSerial;

    /**
     * Search for ClassCache object in the given scope.
     * The method first calls
     * {@link ScriptableObject#getTopLevelScope(Scriptable scope)}
     * to get the top most scope and then tries to locate associated
     * ClassCache object in the prototype chain of the top scope.
     *
     * @param scope scope to search for ClassCache object.
     * @return previously associated ClassCache object or a new instance of
     *         ClassCache if no ClassCache object was found.
     *
     * @see #associate(ScriptableObject topScope)
     */
    public static ClassCache get(Scriptable scope)
    {
        ClassCache cache;
        cache = (ClassCache)ScriptableObject.getTopScopeValue(scope, AKEY);
        if (cache == null) {
            // XXX warn somehow about wrong cache usage ?
            cache = new ClassCache();
        }
        return cache;
    }

    /**
     * Associate ClassCache object with the given top-level scope.
     * The ClassCache object can only be associated with the given scope once.
     *
     * @param topScope scope to associate this ClassCache object with.
     * @return true if no prevous ClassCache objects were embedded into
     *         the scope and this ClassCache were successfully associated
     *         or false otherwise.
     *
     * @see #get(Scriptable scope)
     */
    public boolean associate(ScriptableObject topScope)
    {
        if (topScope.getParentScope() != null) {
            // Can only associate cache with top level scope
            throw new IllegalArgumentException();
        }
        if(this == topScope.associateValue(AKEY, this)) {
            scope = topScope;
            return true;
        }
        return false;
    }

    /**
     * Empty caches of generated Java classes and Java reflection information.
     */
    public synchronized void clearCaches()
    {
        classTable = new Hashtable();
        javaAdapterGeneratedClasses = new Hashtable();
        interfaceAdapterCache = null;
    }

    /**
     * Check if generated Java classes and Java reflection information
     * is cached.
     */
    public final boolean isCachingEnabled()
    {
        return cachingIsEnabled;
    }

     /**
     * Set whether to cache some values.
     * <p>
     * By default, the engine will cache the results of
     * <tt>Class.getMethods()</tt> and similar calls.
     * This can speed execution dramatically, but increases the memory
     * footprint. Also, with caching enabled, references may be held to
     * objects past the lifetime of any real usage.
     * <p>
     * If caching is enabled and this method is called with a
     * <code>false</code> argument, the caches will be emptied.
     * <p>
     * Caching is enabled by default.
     *
     * @param enabled if true, caching is enabled
     *
     * @see #clearCaches()
     */
    public synchronized void setCachingEnabled(boolean enabled)
    {
        if (enabled == cachingIsEnabled)
            return;
        if (!enabled)
            clearCaches();
        cachingIsEnabled = enabled;
    }

    /**
     * @deprecated
     * The method always returns false.
     * @see #setInvokerOptimizationEnabled(boolean enabled)
     */
    public boolean isInvokerOptimizationEnabled()
    {
        return false;
    }

    /**
     * @deprecated
     * The method does nothing.
     * Invoker optimization is no longer used by Rhino.
     * On modern JDK like 1.4 or 1.5 the disadvatages of the optimization
     * like incresed memory usage or longer initialization time overweight
     * small speed increase that can be gained using generated proxy class
     * to replace reflection.
     */
    public synchronized void setInvokerOptimizationEnabled(boolean enabled)
    {
    }

    /**
     * Internal engine method to return serial number for generated classes
     * to ensure name uniqueness.
     */
    public final synchronized int newClassSerialNumber()
    {
        return ++generatedClassSerial;
    }

    Object getInterfaceAdapter(Class cl)
    {
        Object result;
        Hashtable cache = interfaceAdapterCache;
        if (cache == null) {
            result = null;
        } else {
            result = cache.get(cl);
        }
        return result;
    }

    synchronized void cacheInterfaceAdapter(Class cl, Object iadapter)
    {
        if (cachingIsEnabled) {
            if (interfaceAdapterCache == null) {
                interfaceAdapterCache = new Hashtable();
            }
            interfaceAdapterCache.put(cl, iadapter);
        }
    }
}