kevinrr888 commented on code in PR #28: URL: https://github.com/apache/accumulo-classloaders/pull/28#discussion_r2456380393
########## modules/vfs-class-loader/src/main/java/org/apache/accumulo/classloader/vfs/HDFSContextClassLoaderFactory.java: ########## @@ -0,0 +1,186 @@ +/* + * 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 + * + * https://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.accumulo.classloader.vfs; + +import java.io.IOException; +import java.net.URL; +import java.net.URLClassLoader; +import java.nio.file.Files; +import java.util.List; + +import org.apache.accumulo.core.spi.common.ContextClassLoaderFactory; +import org.apache.hadoop.fs.FileSystem; +import org.apache.hadoop.fs.Path; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import com.google.common.annotations.VisibleForTesting; +import com.google.common.cache.Cache; +import com.google.common.cache.CacheBuilder; +import com.google.gson.Gson; + +/** + * A {@link ContextClassLoaderFactory} implementation which uses a {@link URLClassLoader} per + * defined context. To use this class, need to set the Accumulo configuration property + * <b>general.context.class.loader.factory</b> to the fully qualified name of this class. <br> + * <br> + * Configuration of this class is done by having a base directory in HDFS which stores context + * directories (e.g., hdfs://test:1234/contexts could be the base directory) and where the children + * are specific contexts (e.g., contextA, contextB). To set the HDFS file system for this class, use + * {@link HDFSContextClassLoaderFactory#setHDFSFileSystem(FileSystem)}. The "contexts" directory + * should not contain any other files or directories. Each context directory should contain a + * manifest file <b>manifest.json</b> and JAR files. The manifest file defines the context name and + * the JAR info for what JARs should be in the {@link URLClassLoader} for that context. For example: + * + * <pre> + * { + * "context": "contextA", + * "jars": [ + * { + * "name": "Iterators.jar", + * "checksum": "f2ca1bb6c7e907d06dafe4687e579fce76b37e4e93b7605022da52e6ccc26fd2" + * }, + * { + * "name": "IteratorsV2.jar", + * "checksum": "934ee77f70dc82403618c154aa63af6f4ebbe3ac1eaf22df21e7e64f0fb6643d" + * } + * ] + * } + * </pre> + * + * Two system properties need to be set to use this class: <br> + * <b>hdfs.contexts.class.loader.base.dir</b> <br> + * This defines where the context directories exist within HDFS (e.g., hdfs://test:1234/contexts in + * our example) <br> + * <b>local.contexts.class.loader.download.dir</b> <br> + * This defines where the context info will be locally downloaded to. This includes the manifest + * file(s) and JAR(s). For example, if set to "/path/to/contexts" and + * {@link HDFSContextClassLoaderFactory#getClassLoader(String)} is called with the argument + * "contextA", will create the local directory "/path/to/contexts/contextA" (note that all parent + * directories will be created if needed), will download the manifest file from HDFS to the contextA + * directory, and will download the JARs Iterators.jar and IteratorsV2.jar from HDFS to the contextA + * directory. The {@link URLClassLoader} will be constructed from these local JARs, will be + * associated with "contextA", and will be cached. + */ +public class HDFSContextClassLoaderFactory implements ContextClassLoaderFactory { + private static final Logger LOG = LoggerFactory.getLogger(HDFSContextClassLoaderFactory.class); + public static final String MANIFEST_FILE_NAME = "manifest.json"; + public static final String HDFS_CONTEXTS_BASE_DIR = "hdfs.contexts.class.loader.base.dir"; + public static final String LOCAL_CONTEXTS_DOWNLOAD_DIR = + "local.contexts.class.loader.download.dir"; + // Cache the class loaders for re-use + // WeakReferences are used so that the class loaders can be cleaned up when no longer needed + // Classes that are loaded contain a reference to the class loader used to load them + // so the class loader will be garbage collected when no more classes are loaded that reference it + private final Cache<Path,URLClassLoader> classLoaders = + CacheBuilder.newBuilder().weakValues().build(); + private FileSystem fs; + + public void setHDFSFileSystem(FileSystem fs) { + this.fs = fs; + } + + @VisibleForTesting + public static class Context { + private final String contextName; + private final List<JarInfo> jars; + + public Context(String contextName, JarInfo... jars) { + this.contextName = contextName; + this.jars = List.of(jars); + } + + public String getContextName() { + return contextName; + } + + public List<JarInfo> getJars() { + return jars; + } + } + + @VisibleForTesting + public static class JarInfo { + private final String jarName; + private final String checksum; + + public JarInfo(String jarName, String checksum) { + this.jarName = jarName; + this.checksum = checksum; + } + + public String getJarName() { + return jarName; + } + + public String getChecksum() { + return checksum; + } + } + + private URLClassLoader createClassLoader(String contextName, Path HDFSManifestFile) + throws IOException, ContextClassLoaderException { + var localContextsDownloadDirStr = System.getProperty(LOCAL_CONTEXTS_DOWNLOAD_DIR); + var localContextDownloadDir = java.nio.file.Path.of(localContextsDownloadDirStr, contextName); + if (localContextDownloadDir.toFile().mkdirs()) { + LOG.info("Created dir(s) " + localContextDownloadDir); + } + + var localManifestFile = localContextDownloadDir.resolve(MANIFEST_FILE_NAME); + fs.copyToLocalFile(HDFSManifestFile, new Path(localManifestFile.toUri())); + LOG.info("Copied manifest file from HDFS {} to local {}", HDFSManifestFile, localManifestFile); Review Comment: I went with this approach initially, but changed to checking the manifest on calls to getClassLoader instead of on an interval. The interval approach does not work when caching values/only storing WeakReferences to the class loader, as the value is not immediately returned to the user, thus no strong reference is made and may be GC'd at any time. Using the approach suggested by @jschmidt10 in https://github.com/apache/accumulo-classloaders/pull/28/#discussion_r2439552053 to first check the modification time, this should be fine/not too expensive to check in getClassLoader I fully explain the problem and my fix in bbc67b6f34a21e20ada727edc7f78cc50d5e3c61 commit message -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
