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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.). 

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. 

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:
     class SomeClass {
         Lock myLock = new Lock();
         void someMethod() {
             myLock.lock();
             try {
                 StartOperation();
                 ContinueOperation();
                 EndOperation();
             } finally {
                 myLock.unlock();
             }
         }
     }

Author:
     Peter King/**
 * 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.
/**
     * 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.
Throws:
InterruptedException – if any thread has
              interrupted this thread./**
     * 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.
/**
     * 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();
    }
}