com.bigdata.relation.accesspath.IAsynchronousIterator Maven / Gradle / Ivy
/*
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
[email protected]
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 27, 2008
*/
package com.bigdata.relation.accesspath;
import java.util.concurrent.TimeUnit;
import com.bigdata.relation.rule.IQueryOptions;
import com.bigdata.relation.rule.IRule;
import cutthecrap.utils.striterators.ICloseableIterator;
/**
* Interface for iterators that are running asynchronously. Such iterators are
* the consumer side of a producer - consumer pattern. The producer writes on an
* {@link IBlockingBuffer} which is drained by the {@link IAsynchronousIterator}.
*
* @author Bryan Thompson
* @version $Id$
*
* @see BlockingBuffer
*/
public interface IAsynchronousIterator extends ICloseableIterator {
// /**
// * Return true if the {@link Future} that is writing on the
// * {@link IBlockingBuffer} has been set and is done. This indicates that all
// * results are materialized on the queue and will be visited without waiting
// * on the {@link Future}. It does NOT indicate whether or not the
// * {@link Future} completely successfully. This method may be used to decide
// * whether or not {@link Iterator#hasNext()} would block. When this method
// * returns true {@link Iterator#hasNext()} should not block
// * because no more elements will be added to the {@link BlockingBuffer}.
// *
// * @return true iff the producer is done.
// */
// public boolean isFutureDone();
/**
* Return true iff this iterator will not visit any more
* elements (non-blocking).
*
* @return true iff the iterator is known to be exhausted
* without blocking. A false return does NOT imply
* that the iterator will visit more elements, only that it MIGHT
* visit more elements.
*/
public boolean isExhausted();
/**
* Return true iff there is at least one element that can be
* visited. If the buffer is empty then this will block until: (a) an
* element appears in the buffer; (b) the buffer is
* {@link BlockingBuffer#close()}ed; or (c) the timeout expires.
*
* Note that a false return DOES NOT signify that the iterator
* is exhausted. However, if you specify an infinite timeout using
* {@link Long#MAX_VALUE} {@link TimeUnit#SECONDS} then you MAY safely
* interpret a false return as an indication that the iterator
* is exhausted.
*
* @param timeout
* The length of time that the method may block awaiting an
* element to appear.
* @param unit
* The units in which the timeout is expressed.
*
* @return true iff there is an element available.
*
* @throws InterruptedException
* if the current thread is interrupted while waiting another
* element.
*/
public boolean hasNext(final long timeout, final TimeUnit unit)
throws InterruptedException;
/**
* Waits up to the timeout to return the next element. When the
* generic type of the elements in the buffer is an array type and there is
* more than one element available within the specified time, then multiple
* elements in the buffer MAY be combined into a single element and that
* element returned to the caller.
*
* @param timeout
* The timeout (overrides the chunkTimeout specified to
* the {@link BlockingBuffer} ctor).
* @param unit
* The unit in which the timeout is expressed.
*
* @return The element -or- null iff the timeout was exceeded
* before {@link #hasNext(long, TimeUnit)} returned
* true.
*
* In order to have a definitive indication that the iterator is
* exhausted you need to invoke {@link #hasNext()} without a timeout
* (blocking) or {@link #isExhausted()} (non-blocking).
*
* @throws InterruptedException
* if the current thread is interrupted while waiting for
* another element.
*/
public E next(long timeout, TimeUnit unit) throws InterruptedException;
/**
* Notes that the iterator is closed and hence may no longer be read. It is
* safe to invoke this method even if the iterator is closed. However, if
* the producer is still running then it will be canceled
* (interrupted) in order to prevent the {@link IBlockingBuffer} from
* filling up and deadlocking. For this reason, {@link #close()} has
* consequences NOT entailed by {@link ICloseableIterator}.
*
* Note: Depending on the semantics of the producer, it MAY choose to treat
* an interrupt() as normal (but eager) termination. For example, rule
* execution treats an interrupt() as normal (but eager) termination with
* the consequence that queries may be safely interrupted once some limit
* has been satisfied. However, the preferred way to treat LIMIT is using
* {@link IRule} with an {@link IQueryOptions} that specifies a LIMIT.
*/
public void close();
}