LockFreeLogger.java revision 2633:b94be69cbb1d 
1/*
2 * Copyright (c) 2014, 2017, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 */
23
24package jdk.test.lib;
25
26import java.util.Collection;
27import java.util.Comparator;
28import java.util.Map;
29import java.util.concurrent.ConcurrentHashMap;
30import java.util.concurrent.ConcurrentLinkedQueue;
31import java.util.concurrent.atomic.AtomicInteger;
32import java.util.stream.Collectors;
33
34/**
35 * A logger designed specifically to allow collecting ordered log messages
36 * in a multi-threaded environment without involving any kind of locking.
37 * <p>
38 * It is particularly useful in situations when one needs to assert various
39 * details about the tested thread state or the locks it hold while also wanting
40 * to produce diagnostic log messages.
41 * <p>
42 * The logger does not provide any guarantees about the completness of the
43 * logs written from different threads - it is up to the caller to make sure
44 * {@code toString()} method is called only when all the activity has ceased
45 * and the per-thread logs contain all the necessary data.
46 *
47 * @author Jaroslav Bachorik
48 **/
49public class LockFreeLogger {
50    private final AtomicInteger logCntr = new AtomicInteger(0);
51    private final Collection<Map<Integer, String>> allRecords = new ConcurrentLinkedQueue<>();
52    private final ThreadLocal<Map<Integer, String>> records = ThreadLocal.withInitial(ConcurrentHashMap::new);
53
54    public LockFreeLogger() {
55        allRecords.add(records.get());
56    }
57
58    /**
59     * Log a message
60     * @param format Message format
61     * @param params Message parameters
62     */
63    public void log(String format, Object ... params) {
64        int id = logCntr.getAndIncrement();
65        records.get().put(id, String.format(format, params));
66    }
67
68    /**
69     * Will generate an aggregated log of chronologically ordered messages.
70     * <p>
71     * Make sure that you call this method only when all the related threads
72     * have finished; otherwise you might get incomplete data.
73     *
74     * @return An aggregated log of chronologically ordered messages
75     */
76    @Override
77    public String toString() {
78        return allRecords.stream()
79            .flatMap(m -> m.entrySet().stream())
80            .sorted(Comparator.comparing(Map.Entry::getKey))
81            .map(Map.Entry::getValue)
82            .collect(Collectors.joining());
83    }
84}
85