GridClassLoaderCache.java

/* 
 Copyright (C) GridGain Systems. All Rights Reserved.
 
 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 org.gridgain.grid.util;

import org.gridgain.grid.util.typedef.*;
import org.gridgain.grid.util.typedef.internal.*;
import org.jdk8.backport.*;

import java.util.*;
import java.util.concurrent.*;

/**
 * Caches class loaders for classes.
 */
public final class GridClassLoaderCache {
    /** Fields cache. */
    private static final ConcurrentMap<Class<?>, ClassLoader> cache =
        new ConcurrentHashMap8<>();

    /**
     * Gets cached ClassLoader for efficiency since class loader detection has proven to be slow.
     *
     * @param cls Class.
     * @return ClassLoader for the class.
     */
    public static ClassLoader classLoader(Class<?> cls) {
        ClassLoader cached = cache.get(cls);

        if (cached == null) {
            ClassLoader old = cache.putIfAbsent(cls, cached = detectClassLoader(cls));

            if (old != null)
                cached = old;
        }

        return cached;
    }

    /**
     * @param ldr Undeployed class loader.
     */
    public static void onUndeployed(ClassLoader ldr) {
        assert ldr != null;

        for (Map.Entry<Class<?>, ClassLoader> e : cache.entrySet()) {
            if (e.getValue().equals(ldr))
                cache.remove(e.getKey(), ldr);
        }
    }

    /**
     * Detects class loader for given class.
     * <p>
     * This method will first check if {@link Thread#getContextClassLoader()} is appropriate.
     * If yes, then context class loader will be returned, otherwise
     * the {@link Class#getClassLoader()} will be returned.
     *
     * @param cls Class to find class loader for.
     * @return Class loader for given class (never {@code null}).
     */
    private static ClassLoader detectClassLoader(Class<?> cls) {
        ClassLoader ctxClsLdr = Thread.currentThread().getContextClassLoader();

        ClassLoader clsLdr = cls.getClassLoader();

        if (clsLdr == null)
            clsLdr = U.gridClassLoader();

        if (U.p2pLoader(ctxClsLdr))
            return clsLdr;

        if (ctxClsLdr != null) {
            if (ctxClsLdr == clsLdr)
                return ctxClsLdr;

            try {
                // Check if context loader is wider than direct object class loader.
                Class<?> c = Class.forName(cls.getName(), true, ctxClsLdr);

                if (c == cls)
                	/**
                	 * old version code: return ctxClsLdr;
                	 * update reason:    JDK class should not loaded by GridUriDeploymentClassLoader
                	 * update time:      2014-12-12
                	 * update by:        WangWei
                	 */
                    return cls.getClassLoader() == null ? ClassLoader.getSystemClassLoader() : ctxClsLdr;
            }
            catch (ClassNotFoundException ignored) {
                // No-op.
            }
        }

        return clsLdr;
    }
    
    /**
     *
     */
    public static void printMemoryStats() {
        X.println(">>>");
        X.println(">>> GridClassLoaderCache memory stats:");
        X.println(" Cache size: " + cache.size());

        for (Map.Entry<Class<?>, ClassLoader> e : cache.entrySet())
            X.println(" " + e.getKey() + " : " + e.getValue());
    }

    /**
     * Intended for test purposes only.
     */
    public static void clear() {
        cache.clear();
    }

    /**
     * Ensure singleton.
     */
    private GridClassLoaderCache() {
        // No-op.
    }
}