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From ottobackwards <...@git.apache.org>
Subject [GitHub] metron pull request #530: METRON-777 Metron Extension System and Parser Exte...
Date Tue, 08 Aug 2017 16:44:40 GMT
Github user ottobackwards commented on a diff in the pull request:

    https://github.com/apache/metron/pull/530#discussion_r131967527
  
    --- Diff: bundles-lib/src/main/java/org/apache/metron/bundles/BundleClassLoaders.java
---
    @@ -0,0 +1,353 @@
    +/*
    + * 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.metron.bundles;
    +
    +import java.net.URISyntaxException;
    +import java.util.*;
    +
    +import org.apache.commons.collections.CollectionUtils;
    +import org.apache.commons.vfs2.FileObject;
    +import org.apache.commons.vfs2.FileSystemException;
    +import org.apache.commons.vfs2.FileSystemManager;
    +import org.apache.metron.bundles.bundle.Bundle;
    +import org.apache.metron.bundles.bundle.BundleCoordinate;
    +import org.apache.metron.bundles.bundle.BundleDetails;
    +import org.apache.metron.bundles.util.BundleProperties;
    +import org.apache.metron.bundles.util.BundleSelector;
    +import org.apache.metron.bundles.util.FileUtils;
    +import org.apache.metron.bundles.util.BundleUtil;
    +import org.slf4j.Logger;
    +import org.slf4j.LoggerFactory;
    +
    +/**
    + * A singleton class used to initialize the extension and framework classloaders.
    + */
    +public final class BundleClassLoaders {
    +
    +  private static volatile BundleClassLoaders bundleClassLoaders;
    +  private volatile InitContext initContext;
    +  private static final Logger logger = LoggerFactory.getLogger(BundleClassLoaders.class);
    +
    +  private final static class InitContext {
    +
    +    private final List<FileObject> extensionDirs;
    +    private final Map<String, Bundle> bundles;
    +
    +    private InitContext(
    +        final List<FileObject> extensionDirs,
    +        final Map<String, Bundle> bundles) {
    +      this.extensionDirs = extensionDirs;
    +      this.bundles = bundles;
    +    }
    +  }
    +
    +  private BundleClassLoaders() {
    +  }
    +
    +  /**
    +   * @return The singleton instance of the BundleClassLoaders
    +   */
    +  public static BundleClassLoaders getInstance() {
    +    BundleClassLoaders result = bundleClassLoaders;
    +    if (result == null) {
    +      synchronized (BundleClassLoaders.class) {
    +        result = bundleClassLoaders;
    +        if (result == null) {
    +          bundleClassLoaders = result = new BundleClassLoaders();
    +        }
    +      }
    +    }
    +    return result;
    +  }
    +
    +  public static void reset() {
    +    getInstance().unInit();
    +  }
    +
    +  private void unInit() {
    +    synchronized (this) {
    +      initContext = null;
    +    }
    +  }
    +
    +  /**
    +   * Initializes and loads the BundleClassLoaders. This method must be called before
the rest of the
    +   * methods to access the classloaders are called and it can be safely called any number
of times
    +   * provided the same framework and extension working dirs are used.
    +   *
    +   * @param fileSystemManager the FileSystemManager
    +   * @param extensionsDirs where to find extension artifacts
    +   * @param props BundleProperties
    +   * @throws FileSystemException if any issue occurs while exploding bundle working directories.
    +   * @throws java.lang.ClassNotFoundException if unable to load class definition
    +   * @throws IllegalStateException already initialized with a given pair of directories
cannot
    +   * reinitialize or use a different pair of directories.
    +   */
    +  public void init(final FileSystemManager fileSystemManager, final List<FileObject>
extensionsDirs,
    +      BundleProperties props)
    +      throws FileSystemException, ClassNotFoundException, URISyntaxException {
    +    if (extensionsDirs == null || fileSystemManager == null) {
    +      throw new NullPointerException("cannot have empty arguments");
    +    }
    +    InitContext ic = initContext;
    +    if (ic == null) {
    +      synchronized (this) {
    +        ic = initContext;
    +        if (ic == null) {
    +          initContext = ic = load(fileSystemManager, extensionsDirs, props);
    +        }
    +      }
    +    } else {
    +      boolean matching = CollectionUtils
    +          .isEqualCollection(initContext.extensionDirs, extensionsDirs);
    +      if (!matching) {
    +        throw new IllegalStateException(
    +            "Cannot reinitialize and extension/framework directories cannot change");
    +      }
    +    }
    +  }
    +
    +  /**
    +   * Should be called at most once.
    +   */
    +  private InitContext load(final FileSystemManager fileSystemManager,
    +      final List<FileObject> extensionsDirs, BundleProperties props)
    +      throws FileSystemException, ClassNotFoundException, URISyntaxException {
    +    // get the system classloader
    +    final ClassLoader systemClassLoader = ClassLoader.getSystemClassLoader();
    +
    +    // find all bundle files and create class loaders for them.
    --- End diff --
    
    There are a couple of things to think about here.
    
    * loading too many extensions
    * loading extensions of types we are not going to use or need
    
    We load all the parser extension bundles in each topology, and only 'use' one.
    If we had new extension types, let's say for.... indexing ;) then we would load the all
the indexing and all the parser extensions, but only call on what was specified.
    
    This is an efficiency issue only I think, meaning I don't think there is any issue with
how things 'work'.
    
    We can sub divide the extension library by types (stellar, parser, indexing), and then
'inject' the composite library directory lists through the properties.
    
    I don't think it is worth it to configure specific bundle names.
    
    I would like to think about making it more 'lazy loading' though
    
    



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