Github user mattf-horton commented on a diff in the pull request:
    --- Diff: 
bundles-lib/src/main/java/org/apache/metron/bundles/ ---
    @@ -0,0 +1,436 @@
    + * 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
    + *
    + *
    + *
    + * 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 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.BundleCoordinates;
    +import org.apache.metron.bundles.bundle.BundleDetails;
    +import org.apache.metron.bundles.util.BundleProperties;
    +import org.apache.metron.bundles.util.FileUtils;
    +import org.apache.metron.bundles.util.StringUtils;
    +import org.atteo.classindex.ClassIndex;
    +import org.slf4j.Logger;
    +import org.slf4j.LoggerFactory;
    +import java.lang.reflect.Modifier;
    +import java.util.*;
    +import java.util.concurrent.ConcurrentHashMap;
    +import java.util.concurrent.atomic.AtomicBoolean;
    + * Scans through the classpath to load all extension components using the 
service provider API and
    + * running through all classloaders (root, BUNDLEs).
    + *
    + * @ThreadSafe - is immutable
    --- End diff --
    I'm worried about ExtensionManager.  It is effectively a fully static 
class, hence a de-facto singleton.
    But the implementor seems under the impression that by making all top-level 
static fields "final", that somehow makes it threadsafe.
    Which is blatantly untrue, since those fields contain data structures that 
are not immutable, and in most cases not concurrent.
    Also, it probably currently works because it is only called once at startup 
time.  But I'm concerned what happens if it gets called from multiple 
topologies running in the same VM. And it certainly won't work for dynamic 
addition of bundles during runtime.
    Let me emphasize again: This class is NOT threadsafe.  @ottobackwards , if 
you believe it needs to be threadsafe, then please do a reset and discuss with 
me how to fix this.  If it's probably okay for current usages, then it is 
sufficient to mention it for improvement in a jira.  Do you think METRON-1100 
is an okay place for such mention, or should we open another jira?

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