Github user mattf-horton commented on a diff in the pull request:
https://github.com/apache/metron/pull/530#discussion_r133037865
--- Diff:
bundles-lib/src/main/java/org/apache/metron/bundles/BundleClassLoaders.java ---
@@ -0,0 +1,376 @@
+/*
+ * 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 com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
+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.BundleCoordinates;
+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);
+
+ /**
+ * Holds the context from {@code BundleClassLoaders} initialization,
+ * being the coordinate to bundle mapping.
+ *
+ * After initialization these are not changed, and as such they
+ * are immutable.
+ *
+ */
+ private final static class InitContext {
+
+ private final List<FileObject> extensionDirs;
+ private final Map<String, Bundle> bundles;
+ private final BundleProperties properties;
+
+ private InitContext(
+ final List<FileObject> extensionDirs,
+ final Map<String, Bundle> bundles,
+ final BundleProperties properties) {
+ this.extensionDirs = ImmutableList.copyOf(extensionDirs);
+ this.bundles = ImmutableMap.copyOf(bundles);
+ this.properties = properties;
+ }
+ }
+
+ 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 = new BundleClassLoaders();
+ result = bundleClassLoaders;
+ }
+ }
+ }
+ return result;
+ }
+
+ /**
+ * Uninitializes the BundleClassloaders. After calling this
<code>init</code> must be called
+ * before the rest of the methods are called afterwards.
+ * This is for TESTING ONLY at this time. Reset does not unload or
clear any loaded classloaders.
+ */
+ public static void reset() {
+ synchronized (BundleClassLoaders.class) {
+ getInstance().unInit();
+ bundleClassLoaders = null;
+ }
+ }
+
+ private void unInit() {
+ synchronized (this) {
+ if(initContext != null) {
+ initContext = null;
+ }
--- End diff --
Recommend combining reset and unInit methods. This avoids the issues of
- having reset static while unInit is per-instance (doesn't matter which
since is singleton, but confusing to use both)
- using double synchronize calls (ok even with both static or both
per-instance, because Java locks are reentrant, but unnecessary and raises
concerns in paranoid reviewers like me)
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