dlmarion commented on code in PR #30: URL: https://github.com/apache/accumulo-classloaders/pull/30#discussion_r2546010755
########## modules/local-caching-classloader/README.md: ########## @@ -0,0 +1,69 @@ +<!-- +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. +--> + +# Local Caching ClassLoader + +The LocalCachingContextClassLoaderFactory is an Accumulo ContextClassLoaderFactory implementation that creates and maintains a +LocalCachingContext. The `LocalCachingContextClassLoaderFactory.getClassLoader(String)` method expects the method +argument to be a valid `file`, `hdfs`, `http` or `https` URL to a context definition file. + +The context definition file is a JSON formatted file that contains the name of the context, the interval in seconds at which +the context definition file should be monitored, and a list of classpath resources. The LocalCachingContextClassLoaderFactory +creates the LocalCachingContext based on the initial contents of the context definition file, and updates the classloader +as changes are noticed based on the monitoring interval. An example of the context definition file is below. + +``` +{ + "contextName": "myContext", + "monitorIntervalSeconds": 5, + "resources": [ + { + "location": "file:/home/user/ClassLoaderTestA/TestA.jar", + "checksum": "a10883244d70d971ec25cbfa69b6f08f" + }, + { + "location": "hdfs://localhost:8020/contextB/TestB.jar", + "checksum": "a02a3b7026528156fb782dcdecaaa097" + }, + { + "location": "http://localhost:80/TestC.jar";, + "checksum": "f464e66f6d07a41c656e8f4679509215" + } + ] +} +``` + +The system property `accumulo.classloader.cache.dir` is required to be set to a local directory on the host. The +LocalCachingContext creates a directory at this location for each named context. Each context cache directory +contains a lock file and a copy of each fetched resource that is named in the context definition file using the format: +`fileName_checksum`. The lock file is used with Java's `FileChannel.tryLock` to enable exclusive access (on supported +platforms) to the directory from different processes on the same host. + +## Cleanup + +Because the cache directory is shared among multiple processes, and one process can't know what the other processes are doing, +this class cannot clean up the shared cache directory. It is left to the user to remove unused context cache directories and unused old files within a context cache directory. Review Comment: I think that @ctubbsii is working on something like this as a modification to this PR -- 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]
