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https://issues.apache.org/jira/browse/METRON-777?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16124289#comment-16124289
]
ASF GitHub Bot commented on METRON-777:
---------------------------------------
Github user mattf-horton commented on a diff in the pull request:
https://github.com/apache/metron/pull/530#discussion_r132798637
--- Diff:
bundles-lib/src/main/java/org/apache/metron/bundles/ExtensionManager.java ---
@@ -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
+ *
+ * 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 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.apache.metron.bundles.annotation.behavior.RequiresInstanceClassLoading;
+
+import org.atteo.classindex.ClassIndex;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.lang.reflect.Modifier;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.net.URL;
+import java.net.URLClassLoader;
+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?
> Create a plugin system for Metron based on 'NAR'
> ------------------------------------------------
>
> Key: METRON-777
> URL: https://issues.apache.org/jira/browse/METRON-777
> Project: Metron
> Issue Type: New Feature
> Reporter: Otto Fowler
> Assignee: Otto Fowler
>
> The success of the Metron project will be greatly dependent on community
> participation, and with that the ability to adapt and extend Metron without
> having to maintain a fork of the project.
> As organizations and individuals look to extend the Metron system with custom
> parsers, enrichments, and stellar functions that may be proprietary in
> nature, the ability to develop and deploy these extensions outside the Metron
> code base is critically important.
> To that end, and after community discussion and proposal we create or
> formalize the 'plugin' development story in Metron.
> The proposal is to adapt the Apache Nifi NAR system for use in Metron. This
> will provide the system with:
> * archetype(s) for developer projects and independent development
> * defined packaging and metadata for 'plugin' products
> * loading and instantiation with classloader isolation capabilities
> * removing the necessity for shading plugin jars
> These capabilities will also enable other features, such as plugin lifecycle,
> plugin configuration+redeployment, and other things.
> The plugin archetypes and their installation will be a followon
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