Github user mattf-horton commented on a diff in the pull request: https://github.com/apache/metron/pull/530#discussion_r131966450 --- 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. --- End diff -- I don't understand. I'm pretty sure that all Storm bolts on the same physical host run in the same JVM. At least all bolts in the same Supervisor do; I'm not sure if you can run multiple supers on a single host. So any single-node cluster is going to have the potential to run multiple parser plugins in the same JVM, but even multi-node clusters might -- it's up to the Master.
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