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https://issues.apache.org/jira/browse/METRON-777?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16124288#comment-16124288
]
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_r132800554
--- Diff:
bundles-lib/src/main/java/org/apache/metron/bundles/BundleThreadContextClassLoader.java
---
@@ -0,0 +1,221 @@
+/*
+ * 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.io.IOException;
+import java.io.InputStream;
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.ArrayList;
+import java.util.Enumeration;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import org.apache.metron.bundles.bundle.Bundle;
+import org.apache.metron.bundles.util.BundleProperties;
+
+/**
+ * THREAD SAFE
+ */
+public class BundleThreadContextClassLoader extends URLClassLoader {
+
+ static final ContextSecurityManager contextSecurityManager = new
ContextSecurityManager();
+ private final ClassLoader forward = ClassLoader.getSystemClassLoader();
+ private static final List<Class<?>> bundleSpecificClasses = new
ArrayList<>();
+ private static AtomicBoolean inited = new AtomicBoolean(false);
+ // should initialize class definitions
+ public static void initClasses(final List<Class> classes){
--- End diff --
The comparable code in Nifi used a static initializer to init the classes
list.
This uses a public method, and an AtomicBoolean flag to say it's been done.
Why doesn't the initClasses() method need to be synchronized?
(BTW, I really dislike these all-static or mostly-static classes, which
seem to be trying to be singletons without engaging in the discipline of
singleton-ness, especially wrt thread safeness. But I understand they
originated in the nifi code, so I'm not after you about that :-)
> 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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