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    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   }

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