Java tutorial
/** * 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.pig; import java.lang.reflect.Method; import java.lang.reflect.Modifier; import java.util.ArrayList; import java.util.List; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.pig.classification.InterfaceAudience; import org.apache.pig.classification.InterfaceStability; /** * This class is used to manage JVM Reuse in case of execution engines like Tez * and Spark. * * Static data members of a UDF, LoadFunc or StoreFunc class * need to be reset or object references made null or reinitialized * when the jvm container is reused for new tasks. * * Example usage to perform static data cleanup in a UDF as follows. * * public class MyUDF extends EvalFunc<Tuple> { * private static int numInvocations = 0; * private static Reporter reporter; * * static { * // Register this class for static data cleanup * JVMReuseManager.getInstance().registerForStaticDataCleanup(MyUDF.class); * } * * // Write a public static method that performs the cleanup * // and annotate it with @StaticDataCleanup * @StaticDataCleanup * public static void staticDataCleanup() { * numInvocations = 0; * reporter = null; * } * #### UDF Code goes here ###### * } * * @since Pig 0.14 */ @InterfaceAudience.Public @InterfaceStability.Stable public class JVMReuseManager { private static Log LOG = LogFactory.getLog(JVMReuseImpl.class); private List<Method> cleanupMethods = new ArrayList<Method>(); private static JVMReuseManager instance = new JVMReuseManager(); private JVMReuseManager() { } public static JVMReuseManager getInstance() { return instance; } public void registerForStaticDataCleanup(Class<?> clazz) { for (Method method : clazz.getMethods()) { if (method.isAnnotationPresent(StaticDataCleanup.class)) { if (!(Modifier.isStatic(method.getModifiers()) && Modifier.isPublic(method.getModifiers()))) { throw new RuntimeException("Method " + method.getName() + " in class " + clazz.getName() + "should be public and static as it is annotated with "); } LOG.debug("Method " + method.getName() + " in class " + method.getDeclaringClass() + " registered for static data cleanup"); instance.cleanupMethods.add(method); } } } List<Method> getStaticDataCleanupMethods() { return cleanupMethods; } }