/**
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
licenses@blazegraph.com
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program 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 for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/*
* Created on Aug 16, 2011
*/
package com.bigdata.bop;
/**
* An interface providing access to named attribute values which may be shared
* across operators or across multiple invocations of the same operator. The
* bindings are scoped to the owning {@link IQueryContext}.
* <p>
* The key MUST include enough information to provide for the scope of the
* attribute within the query and is typically the bop identifier plus an
* attribute name. Bindings DO NOT cross a service partition so it is not
* necessary to add the shardId or service UUID to the key.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
*/
public interface IQueryAttributes {
/**
* Return the attribute value under the key.
*
* @param key
* The key.
*
* @return The attribute value under that key -or- <code>null</code> if
* there is no bound attribute for that key.
*/
Object get(Object key);
/**
* Bind an attribute under the key.
*
* @param key
* The key.
* @param val
* The new value (may not be <code>null</code>).
*
* @return The old value.
*
* @see #get(Object)
*/
Object put(Object key, Object val);
/**
* Atomically bind an attribute value under the key iff the key is not
* already bound.
*
* @param key
* The key.
* @param val
* The new value (may not be <code>null</code>).
*
* @return The old value.
*/
Object putIfAbsent(Object key, Object val);
/**
* Remove the attribute under the key.
*
* @param key
* The key.
*
* @return The old value.
*/
Object remove(Object key);
/**
* Atomically remove the attribute under the key iff it has the given value.
*
* @param key
* The key.
* @param value
* The expected value for that key.
*
* @return <code>true</code> iff the entry for that key was removed.
*/
boolean remove(Object key,Object value);
}