steveloughran commented on code in PR #4352: URL: https://github.com/apache/hadoop/pull/4352#discussion_r926503951
########## hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/statistics/impl/IOStatisticsContextIntegration.java: ########## @@ -0,0 +1,151 @@ +/* + * 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.hadoop.fs.statistics.impl; + +import java.lang.ref.WeakReference; +import java.util.concurrent.atomic.AtomicLong; + +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import org.apache.hadoop.classification.VisibleForTesting; +import org.apache.hadoop.conf.Configuration; +import org.apache.hadoop.fs.impl.WeakReferenceThreadMap; +import org.apache.hadoop.fs.statistics.IOStatisticsContext; + +import static org.apache.hadoop.fs.CommonConfigurationKeys.THREAD_LEVEL_IOSTATISTICS_ENABLED; +import static org.apache.hadoop.fs.CommonConfigurationKeys.THREAD_LEVEL_IOSTATISTICS_ENABLED_DEFAULT; + +/** + * A Utility class for IOStatisticsContext, which helps in creating and + * getting the current active context. Static methods in this class allows to + * get the current context to start aggregating the IOStatistics. + * + * Static initializer is used to work out if the feature to collect + * thread-level IOStatistics is enabled or not and the corresponding + * implementation class is called for it. + * + * Weak Reference thread map to be used to keep track of different context's + * to avoid long-lived memory leakages as these references would be cleaned + * up at GC. + */ +public final class IOStatisticsContextIntegration { + + private static final Logger LOG = + LoggerFactory.getLogger(IOStatisticsContextIntegration.class); + + /** + * Is thread-level IO Statistics enabled? + */ + private static final boolean IS_THREAD_IOSTATS_ENABLED; + + /** + * ID for next instance to create. + */ + public static final AtomicLong INSTANCE_ID = new AtomicLong(1); + + /** + * Active IOStatistics Context containing different worker thread's + * statistics. Weak Reference so that it gets cleaned up during GC and we + * avoid any memory leak issues due to long lived references. + */ + private static final WeakReferenceThreadMap<IOStatisticsContext> + ACTIVE_IOSTATS_CONTEXT = + new WeakReferenceThreadMap<>( + IOStatisticsContextIntegration::createNewInstance, + IOStatisticsContextIntegration::referenceLostContext + ); + + static { + // Work out if the current context has thread level IOStatistics enabled. + final Configuration configuration = new Configuration(); + IS_THREAD_IOSTATS_ENABLED = + configuration.getBoolean(THREAD_LEVEL_IOSTATISTICS_ENABLED, + THREAD_LEVEL_IOSTATISTICS_ENABLED_DEFAULT); + } + + /** + * Private constructor for a utility class to be used in IOStatisticsContext. + */ + private IOStatisticsContextIntegration() {} + + /** + * Creating a new IOStatisticsContext instance for a FS to be used. + * @param key Thread ID that represents which thread the context belongs to. + * @return an instance of IOStatisticsContext. + */ + private static IOStatisticsContext createNewInstance(Long key) { + return new IOStatisticsContextImpl(key, INSTANCE_ID.getAndIncrement()); + } + + /** + * In case of reference loss for IOStatisticsContext. + * @param key ThreadID. + */ + private static void referenceLostContext(Long key) { + LOG.debug("Reference lost for threadID for the context: {}", key); + } + + /** + * Get the current thread's IOStatisticsContext instance. If no instance is + * present for this thread ID, create one using the factory. + * @return instance of IOStatisticsContext. + */ + public static IOStatisticsContext getCurrentIOStatisticsContext() { + return IS_THREAD_IOSTATS_ENABLED + ? ACTIVE_IOSTATS_CONTEXT.getForCurrentThread() + : EmptyIOStatisticsContextImpl.getInstance(); + } + + /** + * Set the IOStatisticsContext for the current thread. + * @param statisticsContext IOStatistics context instance for the + * current thread. + */ + public static void setThreadIOStatisticsContext( + IOStatisticsContext statisticsContext) { + if (IS_THREAD_IOSTATS_ENABLED && + ACTIVE_IOSTATS_CONTEXT.getForCurrentThread() != statisticsContext) { + ACTIVE_IOSTATS_CONTEXT.setForCurrentThread(statisticsContext); Review Comment: will show in a 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. 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