1 /*

     2  * Copyright (c) 1994, 2005, 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.  Oracle designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Oracle in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    22  * or visit www.oracle.com if you need additional information or have any

    23  * questions.

    24  */

    25 

    26 package sun.misc;

    27 

    28 /**

    29  * The Lock class provides a simple, useful interface to a lock.

    30  * Unlike monitors which synchronize access to an object, locks

    31  * synchronize access to an arbitrary set of resources (objects,

    32  * methods, variables, etc.). <p>

    33  *

    34  * The programmer using locks must be responsible for clearly defining

    35  * the semantics of their use and should handle deadlock avoidance in

    36  * the face of exceptions. <p>

    37  *

    38  * For example, if you want to protect a set of method invocations with

    39  * a lock, and one of the methods may throw an exception, you must be

    40  * prepared to release the lock similarly to the following example:

    41  * <pre>

    42  *      class SomeClass {

    43  *          Lock myLock = new Lock();

    44 

    45  *          void someMethod() {

    46  *              myLock.lock();

    47  *              try {

    48  *                  StartOperation();

    49  *                  ContinueOperation();

    50  *                  EndOperation();

    51  *              } finally {

    52  *                  myLock.unlock();

    53  *              }

    54  *          }

    55  *      }

    56  * </pre>

    57  *

    58  * @author      Peter King

    59  */

    60 public

    61 class Lock {

    62     private boolean locked = false;

    63 

    64     /**

    65      * Create a lock, which is initially not locked.

    66      */

    67     public Lock () {

    68     }

    69 

    70     /**

    71      * Acquire the lock.  If someone else has the lock, wait until it

    72      * has been freed, and then try to acquire it again.  This method

    73      * will not return until the lock has been acquired.

    74      *

    75      * @exception  java.lang.InterruptedException if any thread has

    76      *               interrupted this thread.

    77      */

    78     public final synchronized void lock() throws InterruptedException {

    79         while (locked) {

    80             wait();

    81         }

    82         locked = true;

    83     }

    84 

    85     /**

    86      * Release the lock.  If someone else is waiting for the lock, the

    87      * will be notitified so they can try to acquire the lock again.

    88      */

    89     public final synchronized void unlock() {

    90         locked = false;

    91         notifyAll();

    92     }

    93 }