org.apache.accumulo.start.classloader.vfs.AccumuloReloadingVFSClassLoader Maven / Gradle / Ivy

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A library for launching Apache Accumulo services.
There is a newer version: 3.0.0
/*
 * 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 static java.util.concurrent.TimeUnit.SECONDS;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;

import org.apache.commons.vfs2.FileChangeEvent;
import org.apache.commons.vfs2.FileListener;
import org.apache.commons.vfs2.FileObject;
import org.apache.commons.vfs2.FileSystemException;
import org.apache.commons.vfs2.FileSystemManager;
import org.apache.commons.vfs2.impl.DefaultFileMonitor;
import org.apache.commons.vfs2.impl.VFSClassLoader;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Classloader that delegates operations to a VFSClassLoader object. This class also listens for changes in any of the files/directories that are in the
 * classpath and will recreate the delegate object if there is any change in the classpath.
 *
 */
public class AccumuloReloadingVFSClassLoader implements FileListener, ReloadingClassLoader {

  private static final Logger log = LoggerFactory.getLogger(AccumuloReloadingVFSClassLoader.class);

  // set to 5 mins. The rational behind this large time is to avoid a gazillion tservers all asking the name node for info too frequently.
  private static final int DEFAULT_TIMEOUT = 5 * 60 * 1000;

  private FileObject[] files;
  private VFSClassLoader cl;
  private final ReloadingClassLoader parent;
  private final String uris;
  private final DefaultFileMonitor monitor;
  private final boolean preDelegate;
  private final ThreadPoolExecutor executor;
  {
    BlockingQueue queue = new ArrayBlockingQueue(2);
    ThreadFactory factory = new ThreadFactory() {

      @Override
      public Thread newThread(Runnable r) {
        Thread t = new Thread(r);
        t.setDaemon(true);
        return t;
      }

    };
    executor = new ThreadPoolExecutor(1, 1, 1, SECONDS, queue, factory);
  }

  private final Runnable refresher = new Runnable() {
    @Override
    public void run() {
      while (!executor.isTerminating()) {
        try {
          FileSystemManager vfs = AccumuloVFSClassLoader.generateVfs();
          FileObject[] files = AccumuloVFSClassLoader.resolve(vfs, uris);

          log.debug("Rebuilding dynamic classloader using files- " + stringify(files));

          VFSClassLoader cl;
          if (preDelegate)
            cl = new VFSClassLoader(files, vfs, parent.getClassLoader());
          else
            cl = new PostDelegatingVFSClassLoader(files, vfs, parent.getClassLoader());
          updateClassloader(files, cl);
          return;
        } catch (Exception e) {
          log.error("{}", e.getMessage(), e);
          try {
            Thread.sleep(DEFAULT_TIMEOUT);
          } catch (InterruptedException ie) {
            log.error("{}", e.getMessage(), ie);
          }
        }
      }
    }
  };

  public String stringify(FileObject[] files) {
    StringBuilder sb = new StringBuilder();
    sb.append('[');
    String delim = "";
    for (FileObject file : files) {
      sb.append(delim);
      delim = ", ";
      sb.append(file.getName());
    }
    sb.append(']');
    return sb.toString();
  }

  @Override
  public synchronized ClassLoader getClassLoader() {
    if (cl.getParent() != parent.getClassLoader()) {
      scheduleRefresh();
    }
    return cl;
  }

  private void scheduleRefresh() {
    try {
      executor.execute(refresher);
    } catch (RejectedExecutionException e) {
      log.trace("Ignoring refresh request (already refreshing)");
    }
  }

  private synchronized void updateClassloader(FileObject[] files, VFSClassLoader cl) {
    this.files = files;
    this.cl = cl;
  }

  public AccumuloReloadingVFSClassLoader(String uris, FileSystemManager vfs, ReloadingClassLoader parent, long monitorDelay, boolean preDelegate)
      throws FileSystemException {

    this.uris = uris;
    this.parent = parent;
    this.preDelegate = preDelegate;

    ArrayList pathsToMonitor = new ArrayList();
    files = AccumuloVFSClassLoader.resolve(vfs, uris, pathsToMonitor);

    if (preDelegate)
      cl = new VFSClassLoader(files, vfs, parent.getClassLoader());
    else
      cl = new PostDelegatingVFSClassLoader(files, vfs, parent.getClassLoader());

    monitor = new DefaultFileMonitor(this);
    monitor.setDelay(monitorDelay);
    monitor.setRecursive(false);
    for (FileObject file : pathsToMonitor) {
      monitor.addFile(file);
      log.debug("monitoring " + file);
    }
    monitor.start();
  }

  public AccumuloReloadingVFSClassLoader(String uris, FileSystemManager vfs, final ReloadingClassLoader parent, boolean preDelegate) throws FileSystemException {
    this(uris, vfs, parent, DEFAULT_TIMEOUT, preDelegate);
  }

  synchronized public FileObject[] getFiles() {
    return Arrays.copyOf(this.files, this.files.length);
  }

  /**
   * Should be ok if this is not called because the thread started by DefaultFileMonitor is a daemon thread
   */
  public void close() {
    executor.shutdownNow();
    monitor.stop();
  }

  @Override
  public void fileCreated(FileChangeEvent event) throws Exception {
    if (log.isDebugEnabled())
      log.debug(event.getFile().getURL().toString() + " created, recreating classloader");
    scheduleRefresh();
  }

  @Override
  public void fileDeleted(FileChangeEvent event) throws Exception {
    if (log.isDebugEnabled())
      log.debug(event.getFile().getURL().toString() + " deleted, recreating classloader");
    scheduleRefresh();
  }

  @Override
  public void fileChanged(FileChangeEvent event) throws Exception {
    if (log.isDebugEnabled())
      log.debug(event.getFile().getURL().toString() + " changed, recreating classloader");
    scheduleRefresh();
  }

  @Override
  public String toString() {
    StringBuilder buf = new StringBuilder();

    for (FileObject f : files) {
      try {
        buf.append("\t").append(f.getURL().toString()).append("\n");
      } catch (FileSystemException e) {
        log.error("Error getting URL for file", e);
      }
    }

    return buf.toString();
  }

}