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From mattf-horton <...@git.apache.org>
Subject [GitHub] metron pull request #530: METRON-777 Metron Extension System and Parser Exte...
Date Fri, 11 Aug 2017 23:50:28 GMT
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
:-)


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