org.apache.accumulo.start.classloader.vfs.ContextManager.java Source code

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Here is the source code for org.apache.accumulo.start.classloader.vfs.ContextManager.java

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/*
 * 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 org.apache.accumulo.start.classloader.vfs;

import java.io.IOException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import org.apache.commons.vfs2.FileSystemException;
import org.apache.commons.vfs2.FileSystemManager;

public class ContextManager {

    // there is a lock per context so that one context can initialize w/o blocking another context
    private class Context {
        AccumuloReloadingVFSClassLoader loader;
        ContextConfig cconfig;
        boolean closed = false;

        Context(ContextConfig cconfig) {
            this.cconfig = cconfig;
        }

        synchronized ClassLoader getClassLoader() throws FileSystemException {
            if (closed)
                return null;

            if (loader == null) {
                loader = new AccumuloReloadingVFSClassLoader(cconfig.uris, vfs, parent, cconfig.preDelegation);
            }

            return loader.getClassLoader();
        }

        synchronized void close() {
            closed = true;
            if (loader != null) {
                loader.close();
            }
            loader = null;
        }
    }

    private Map<String, Context> contexts = new HashMap<String, Context>();

    private volatile ContextsConfig config;
    private FileSystemManager vfs;
    private ReloadingClassLoader parent;

    ContextManager(FileSystemManager vfs, ReloadingClassLoader parent) {
        this.vfs = vfs;
        this.parent = parent;
    }

    public static class ContextConfig {
        String uris;
        boolean preDelegation;

        public ContextConfig(String uris, boolean preDelegation) {
            this.uris = uris;
            this.preDelegation = preDelegation;
        }

        @Override
        public boolean equals(Object o) {
            if (o instanceof ContextConfig) {
                ContextConfig oc = (ContextConfig) o;

                return uris.equals(oc.uris) && preDelegation == oc.preDelegation;
            }

            return false;
        }

        @Override
        public int hashCode() {
            return uris.hashCode() + (preDelegation ? Boolean.TRUE : Boolean.FALSE).hashCode();
        }
    }

    public interface ContextsConfig {
        ContextConfig getContextConfig(String context);
    }

    public static class DefaultContextsConfig implements ContextsConfig {

        private Iterable<Entry<String, String>> config;

        public DefaultContextsConfig(Iterable<Entry<String, String>> config) {
            this.config = config;
        }

        @Override
        public ContextConfig getContextConfig(String context) {

            String key = AccumuloVFSClassLoader.VFS_CONTEXT_CLASSPATH_PROPERTY + context;

            String uris = null;
            boolean preDelegate = true;

            Iterator<Entry<String, String>> iter = config.iterator();
            while (iter.hasNext()) {
                Entry<String, String> entry = iter.next();
                if (entry.getKey().equals(key)) {
                    uris = entry.getValue();
                }

                if (entry.getKey().equals(key + ".delegation")
                        && entry.getValue().trim().equalsIgnoreCase("post")) {
                    preDelegate = false;
                }
            }

            if (uris != null)
                return new ContextConfig(uris, preDelegate);

            return null;
        }
    }

    /**
     * configuration must be injected for ContextManager to work
     */
    public synchronized void setContextConfig(ContextsConfig config) {
        if (this.config != null)
            throw new IllegalStateException("Context manager config already set");
        this.config = config;
    }

    public ClassLoader getClassLoader(String contextName) throws FileSystemException {

        ContextConfig cconfig = config.getContextConfig(contextName);

        if (cconfig == null)
            throw new IllegalArgumentException("Unknown context " + contextName);

        Context context = null;
        Context contextToClose = null;

        synchronized (this) {
            // only manipulate internal data structs in this sync block... avoid creating or closing classloader, reading config, etc... basically avoid operations
            // that may block
            context = contexts.get(contextName);

            if (context == null) {
                context = new Context(cconfig);
                contexts.put(contextName, context);
            } else if (!context.cconfig.equals(cconfig)) {
                contextToClose = context;
                context = new Context(cconfig);
                contexts.put(contextName, context);
            }
        }

        if (contextToClose != null)
            contextToClose.close();

        ClassLoader loader = context.getClassLoader();
        if (loader == null) {
            // oops, context was closed by another thread, try again
            return getClassLoader(contextName);
        }

        return loader;

    }

    public <U> Class<? extends U> loadClass(String context, String classname, Class<U> extension)
            throws ClassNotFoundException {
        try {
            return getClassLoader(context).loadClass(classname).asSubclass(extension);
        } catch (IOException e) {
            throw new ClassNotFoundException("IO Error loading class " + classname, e);
        }
    }

    public void removeUnusedContexts(Set<String> configuredContexts) {

        Map<String, Context> unused;

        // ContextManager knows of some set of contexts. This method will be called with
        // the set of currently configured contexts. We will close the contexts that are
        // no longer in the configuration.
        synchronized (this) {
            unused = new HashMap<String, Context>(contexts);
            unused.keySet().removeAll(configuredContexts);
            contexts.keySet().removeAll(unused.keySet());
        }

        for (Context context : unused.values()) {
            // close outside of lock
            context.close();
        }
    }
}