/* * Copyright (c) 2014, 2017, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package jdk.test.lib; import java.util.Collection; import java.util.Comparator; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.ConcurrentLinkedQueue; import java.util.concurrent.atomic.AtomicInteger; import java.util.stream.Collectors; /** * A logger designed specifically to allow collecting ordered log messages * in a multi-threaded environment without involving any kind of locking. *

* It is particularly useful in situations when one needs to assert various * details about the tested thread state or the locks it hold while also wanting * to produce diagnostic log messages. *

* The logger does not provide any guarantees about the completness of the * logs written from different threads - it is up to the caller to make sure * {@code toString()} method is called only when all the activity has ceased * and the per-thread logs contain all the necessary data. * * @author Jaroslav Bachorik **/ public class LockFreeLogger { private final AtomicInteger logCntr = new AtomicInteger(0); private final Collection> allRecords = new ConcurrentLinkedQueue<>(); private final ThreadLocal> records = ThreadLocal.withInitial(ConcurrentHashMap::new); public LockFreeLogger() { allRecords.add(records.get()); } /** * Log a message * @param format Message format * @param params Message parameters */ public void log(String format, Object ... params) { int id = logCntr.getAndIncrement(); records.get().put(id, String.format(format, params)); } /** * Will generate an aggregated log of chronologically ordered messages. *

* Make sure that you call this method only when all the related threads * have finished; otherwise you might get incomplete data. * * @return An aggregated log of chronologically ordered messages */ @Override public String toString() { return allRecords.stream() .flatMap(m -> m.entrySet().stream()) .sorted(Comparator.comparing(Map.Entry::getKey)) .map(Map.Entry::getValue) .collect(Collectors.joining()); } }