Java example source code file (Lock.java)

This example Java source code file (Lock.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

interruptedexception, lock

The Lock.java Java example source code

/*
 * Copyright (c) 1994, 2005, 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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 sun.misc;

/**
 * The Lock class provides a simple, useful interface to a lock.
 * Unlike monitors which synchronize access to an object, locks
 * synchronize access to an arbitrary set of resources (objects,
 * methods, variables, etc.). <p>
 *
 * The programmer using locks must be responsible for clearly defining
 * the semantics of their use and should handle deadlock avoidance in
 * the face of exceptions. <p>
 *
 * For example, if you want to protect a set of method invocations with
 * a lock, and one of the methods may throw an exception, you must be
 * prepared to release the lock similarly to the following example:
 * <pre>
 *      class SomeClass {
 *          Lock myLock = new Lock();

 *          void someMethod() {
 *              myLock.lock();
 *              try {
 *                  StartOperation();
 *                  ContinueOperation();
 *                  EndOperation();
 *              } finally {
 *                  myLock.unlock();
 *              }
 *          }
 *      }
 * </pre>
 *
 * @author      Peter King
 */
public
class Lock {
    private boolean locked = false;

    /**
     * Create a lock, which is initially not locked.
     */
    public Lock () {
    }

    /**
     * Acquire the lock.  If someone else has the lock, wait until it
     * has been freed, and then try to acquire it again.  This method
     * will not return until the lock has been acquired.
     *
     * @exception  java.lang.InterruptedException if any thread has
     *               interrupted this thread.
     */
    public final synchronized void lock() throws InterruptedException {
        while (locked) {
            wait();
        }
        locked = true;
    }

    /**
     * Release the lock.  If someone else is waiting for the lock, the
     * will be notitified so they can try to acquire the lock again.
     */
    public final synchronized void unlock() {
        locked = false;
        notifyAll();
    }
}