Source Code for Apache Log4j Core Implementation

Apache Log4j Core Implementation provides the functional components of the logging system. Users are free to create their own plugins and include them in the logging configuration. Apache Log4j Core is a required module to use Apache Log4j.

Bytecode (Java 8) for Apache Log4j Core Implementation is provided in a separate JAR file like log4j-core-2.14.1.jar.

Source Code files for Apache Log4j API are provided in both binary packge like apache-log4j-2.14.1-bin.zip and source package like apache-log4j-2.14.1-src.zip. You can download them at Apache Log4j Website.

You can also browse Source Code files for Apache Log4j Core Implementation 2.14.1 below.

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org/apache/logging/log4j/core/util/CachedClock.java

/*
 * 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.logging.log4j.core.util;

import java.util.concurrent.locks.LockSupport;

/**
 * Implementation of the {@code Clock} interface that tracks the time in a
 * private long field that is updated by a background thread once every
 * millisecond. Timers on most platforms do not have millisecond granularity, so
 * the returned value may "jump" every 10 or 16 milliseconds. To reduce this
 * problem, this class also updates the internal time value every 1024 calls to
 * {@code currentTimeMillis()}.
 */
public final class CachedClock implements Clock {
    private static final int UPDATE_THRESHOLD = 1000;
    private static volatile CachedClock instance;
    private static final Object INSTANCE_LOCK = new Object();
    private volatile long millis = System.currentTimeMillis();
    private short count = 0;

    private CachedClock() {
        final Thread updater = new Log4jThread(() -> {
            while (true) {
                final long time = System.currentTimeMillis();
                millis = time;

                // avoid explicit dependency on sun.misc.Util
                LockSupport.parkNanos(1000 * 1000);
            }
        }, "CachedClock Updater Thread");
        updater.setDaemon(true);
        updater.start();
    }

    public static CachedClock instance() {
        // LOG4J2-819: use lazy initialization of threads
        CachedClock result = instance;
        if (result == null) {
            synchronized (INSTANCE_LOCK) {
                result = instance;
                if (result == null) {
                    instance = result = new CachedClock();
                }
            }
        }
        return result;
    }

    /**
     * Returns the value of a private long field that is updated by a background
     * thread once every millisecond. Timers on most platforms do not
     * have millisecond granularity, the returned value may "jump" every 10 or
     * 16 milliseconds. To reduce this problem, this method also updates the
     * internal time value every 1024 calls.
     * @return the cached time
     */
    @Override
    public long currentTimeMillis() {

        // The count field is not volatile on purpose to reduce contention on this field.
        // This means that some threads may not see the increments made to this field
        // by other threads. This is not a problem: the timestamp does not need to be
        // updated exactly every 1000 calls.
        if (++count > UPDATE_THRESHOLD) {
            millis = System.currentTimeMillis(); // update volatile field: store-store barrier
            count = 0; // after a memory barrier: this change _is_ visible to other threads
        }
        return millis;
    }
}

org/apache/logging/log4j/core/util/CachedClock.java

 

Or download all of them as a single archive file:

File name: log4j-core-2.14.1-sources.jar
File size: 1281358 bytes
Release date: 2021-03-06
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