/*
 * @(#) Lockable.java - Interface for objects synchronized on lock.
 * (c) 2000 Ivan Maidanski <ivmai@chat.ru> http://ivmai.chat.ru
 * Freeware class library sources. All rights reserved.
 **
 * Language: Java [pure]
 * Tested with: JDK v1.1.6
 * Last modified: 2000-12-13 14:50:00 GMT+03:00
 */

/*
 * This software is the proprietary information of the author.
 **
 * Permission to use, copy, and distribute this software and its
 * documentation for non-commercial purposes and without fee is
 * hereby granted provided that this copyright notice appears in all
 * copies.
 **
 * This software should not be modified in any way; any found bug
 * should be reported to the author.
 **
 * The author disclaims all warranties with regard to this software,
 * including all implied warranties of merchantability and fitness.
 * In no event shall the author be liable for any special, indirect
 * or consequential damages or any damages whatsoever resulting from
 * loss of use, data or profits, whether in an action of contract,
 * negligence or other tortuous action, arising out of or in
 * connection with the use or performance of this software.
 */

package ivmai.util;

/**
 * Interface for objects synchronized on lock.
 **
 * A class (typically active) implementing this interface allows an
 * application at any time to choose any custom object on which the
 * instance of the class should perform all its synchronization.
 * This is very useful when several stand-alone active objects (with
 * an internal self-synchronization) need to work in a particular
 * synchronous way (without any possibility of dead-lock).
 **
 * @see ActivityCore
 **
 * @version 2.0
 * @author Ivan Maidanski
 **
 * @since 2.0
 */
public interface Lockable
{

/**
 * Sets new lock object to be used for synchronization.
 **
 * Important notes: inside the class (implementing this interface),
 * <VAR>lock</VAR> should be <CODE>protected transient</CODE> and
 * non-<CODE>null</CODE>, by default <VAR>lock</VAR> is set to
 * <CODE>this</CODE> (during initialization, deserialization or
 * cloning); all needed synchronization (inside/outside the class)
 * must be done on <VAR>lock</VAR> (as shown below). This method
 * should be implemented as follows:
 **
 * <CODE><PRE>
 * protected transient Object lock = this;
 * public final void setLock(Object newLock)
 * throws NullPointerException
 * { // note: take care on deserializing
 * Object curLock;
 * newLock.equals(newLock); // this is a check for null
 * do
 * {
 * synchronized (curLock = lock)
 * {
 * if (curLock == lock)
 * { // check that synchronized on this lock
 * lock = newLock; // this is a synchronized operation
 * break;
 * }
 * }
 * } while (true);
 * }
 * </PRE></CODE>
 **
 * @param newLock
 * a lock object (must be non-<CODE>null</CODE>) to be used by
 * <CODE>this</CODE> object for doing all its synchronization.
 * @exception NullPointerException
 * if <VAR>newLock</VAR> is <CODE>null</CODE>.
 **
 * @see #getLock()
 */
 public abstract void setLock(Object newLock)
  throws NullPointerException;

/**
 * Just returns the current lock object.
 **
 * This method should be implemented as follows:
 **
 * <CODE><PRE>
 * public final Object getLock()
 * {
 * return lock;
 * }
 * </PRE></CODE>
 **
 * @return
 * the current <VAR>lock</VAR> object, on which <CODE>this</CODE>
 * object performs all its synchronization.
 **
 * @see #setLock(java.lang.Object)
 */
 public abstract Object getLock();
}